Draft
Fishery Management Report of the
ATLANTIC STATES MARINE
FISHERIES COMMISSION
Fishery Management Plan for
the Horseshoe Crab
August 1998
FISHERY MANAGEMENT PLAN
FOR THE
HORSESHOE CRAB
Limulus polyphemus
Table of Contents
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Draft
Fishery Management Report
of the
ATLANTIC STATES MARINE FISHERIES COMMISSION
Prepared by the
Horseshoe Crab Plan Development Team
Eric Schrading, USFWS
Thomas O'Connell, Maryland DNR
Stewart Michels, Delaware DNREC
Paul Perra, NMFS
August 1998
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Acknowledgements
The Interstate Fishery Management Plan for the Horseshoe Crab was
developed by the Atlantic States Marine Fisheries Commission.
Members of the Horseshoe Crab Stock Assessment Committee are:
Stewart Michels, Delaware Department of Natural Resources and
Environmental Control; Michael Millard, U.S. Fish and Wildlife
Service; and, Jeffrey Brust, Atlantic States Marine Fisheries
Commission.
Members of the Horseshoe Crab Technical Committee are: Pete
Himchak, New Jersey Fish, Game, and Wildlife; Joanna Burger,
Rutgers University; Stewart Michels, Delaware Department of
Natural Resources and Environmental Control; Tom O'Connell,
Maryland Department of Natural Resources; Larry DeLancey, South
Carolina Department of Natural Resources; Rich Maney, National
Marine Fisheries Service; Anne Rudloe, The Florida State
University; Lewis Gillingham, Commonwealth of Virginia Marine
Fisheries Commission; Byron Young, New York State Department of
Environmental Control; and Gregory Breese, Kevin Moody, and Hal
Laskowski, U.S. Fish and Wildlife Service. The members of the
Advisory Panel also assisted in the development of the Horseshoe
Crab Management Plan.
Special appreciation is extended to many other people who
participated and willingly shared valuable information to assist
in the development of this Plan: John Staples, U.S. Fish and
Wildlife Service; Wennona Brown, U.S. Fish and Wildlife Service
Maryland Coop Unit; Mark Thompson, South Carolina Department of
Natural Resources; Nellie Tsipoura and Dr. Joanna Burger, Rutgers
University; Dr. Mark Botton, Fordham University; Dr. Robert
Loveland, Rutgers University; Brian O'Gorman, National Marine
Fisheries Service; and, Kathy Jo Maio, Maryland Cooperative Fish
and Wildlife Research Unit.
INTERSTATE FISHERY MANAGEMENT PLAN FOR
HORSESHOE CRAB
EXECUTIVE SUMMARY
The horseshoe crab is a benthic or bottom-dwelling arthropod that
utilizes both estuarine and continental shelf habitats. The
horseshoe crab is an ecological generalist and although it is
called a "crab," it is not a true crab, but rather is more
closely related to the arachnids. Horseshoe crabs range from the
Yucatan peninsula to northern Maine. Horseshoe crabs were
traditionally used for fertilizer and livestock food in the late
1800s and early 1900s. During this period of time, harvest was
substantial (over 4 million crabs were landed annually in
Delaware Bay). However, evidence suggests that stocks were
depleted by the 1940s and commercial-scale harvesting of
horseshoe crabs ceased in the 1960s. By the late 1970s,
observations of spawning horseshoe crabs indicated that the
population had substantially recovered. Recently, renewed
commercial interest in horseshoe crabs has been driven by their
use as bait in the American eel and conch pot fisheries, and use
of horseshoe crab blood by the biomedical industry. Between 1990
and 1996, harvest in several states (e.g., New Jersey, Delaware,
and Maryland) has increased. During this period of time, at
least one independent survey (i.e., Delaware trawl survey) has
suggested that the stocks within the Delaware Bay have declined.
The goal of this plan is to conserve and protect the horseshoe
crab resource to ensure its continued role in the ecology of
coastal ecosystems, while providing the opportunity for
commercial, recreational, medical, scientific, and educational
use over time. Specifically, the goal includes management of
horseshoe crab populations for their continued utilization by:
o current and future generations of the fishing and non-
fishing public;
o biomedical industry;
o migrating shorebirds; and,
o other dependent wildlife, including federally listed
sea turtles.
The status of the horseshoe crab populations along the Atlantic
Coast are poorly understood due to the limited amount of
information collected regarding stock levels. Other than the
National Marine Fisheries Service commercial landings data and
trawl surveys, little information was collected until the late
1980s when independent spawning surveys and trawl surveys were
initiated, primarily in the Delaware Bay. Concern over growing
exploitation of the horseshoe crab resource has been expressed by
State and federal fishery resource agencies, conservation
organizations, and fisheries interests. Horseshoe crabs are
important to migrating shorebirds that feed on the eggs; and are
critical to the biomedical industry. Since horseshoe crabs are
slow to mature, they are susceptible to overharvest and
exploitation may adversely affect these other resources.
Currently, horseshoe crabs are commercially harvested for use as
American eel, conch (or whelk), and catfish bait along certain
portions of the Atlantic coast. The horseshoe crab fishery is
unique in that crabs are easily harvested during the spawning
season with minimal financial expense. The eel and conch fishery
is currently dependent on sustained harvest of horseshoe crabs.
The eel fishery targets the use of female horseshoe crabs with
eggs, while the conch fishery uses both males and females. The
reported harvest has increased dramatically in the last five
years. However, improved reporting may be an important component
of increased harvest records.
Horseshoe crabs are an important food source for migrating
shorebirds, finfish, and Atlantic loggerhead turtles, a species
federally listed as threatened pursuant to the Endangered Species
Act (87 Stat. 884, as amended; 16 U.S.C. 1531 et seq.), which use
the Chesapeake Bay as a summer nursery area. Evidence suggests
that the Delaware Bay provides sea turtle nursery habitat as
well. The Delaware Bay is reported to be an important breeding
location for horseshoe crabs and is also the second largest
staging area for shorebirds in North America.
Beach areas provide essential spawning habitat for horseshoe crab
adults. In addition, nearshore, shallow water, intertidal, and
subtidal flats are considered essential habitat for the
development of juvenile horseshoe crabs. Deep water areas are
used by larger juveniles and adults to forage for food. Of the
habitats used by horseshoe crabs, beaches provide the most
critical habitat. The primary threats to essential habitat
include coastal erosion combined with human development
(particularly shoreline stabilization structures such as
bulkheads and revetments) along the estuaries of the Atlantic
Coast.
In order to collect information to assist in future management
decisions, a comprehensive monitoring plan must be instituted
throughout the Atlantic Coast. Such monitoring efforts should be
standardized and occur in each of the cooperating states within
the Atlantic States Marine Fisheries Commission. States that
qualify for "de minimis status," may be exempt from some
monitoring programs.
Each state is responsible for implementing management measures
and protecting horseshoe crab habitat within its jurisdiction to
ensure the sustainability of the population that either is
produced or resides within state boundaries. If current harvest
rates have a substantial impact on the horseshoe crab population,
harvest restrictions would be recommended.
Protection of essential habitat such as spawning beaches and
juvenile nursery habitat is vital to the continued survival of
horseshoe crabs. Each state must identify, categorize, and
prioritize essential horseshoe crab habitats (both spawning and
nursery habitat) within areas of its jurisdiction.
TABLE OF CONTENTS
Page
EXECUTIVE SUMMARY i
LIST OF FIGURES, TABLES, AND APPENDICES vi
LIST OF ACRONYMS AND ABBREVIATIONS vi
1.0. STATUS OF HORSESHOE CRAB RESOURCE 1
1.1. INTRODUCTION 1
1.1.1. Statement of the Problem 1
1.1.2. Benefits of Implementation 1
1.2. DESCRIPTION OF THE RESOURCE 2
1.2.1. Species Life History 2
1.2.2. Stock Assessment Summary 4
1.2.2.1. Distribution 4
1.2.2.2. Sex and Age Ratio 4
1.2.2.3. Stock Assessment 5
1.3. DESCRIPTION OF THE FISHERY 6
1.3.1. Current Fishery Regulations 6
1.3.2. Commercial Fishery 6
1.3.2.1. Bait Fishery 6
1.3.2.2. Biomedical Fishery 11
1.3.3. Recreational Fishery 13
1.4. ECOLOGICAL IMPORTANCE OF HORSESHOE CRABS 13
1.4.1. Shorebirds 13
1.4.2. Finfish 16
1.4.3. Sea Turtles 16
1.5. HABITAT CONSIDERATIONS 16
1.5.1. Description of Habitat 16
1.5.1.1. Spawning Habitat 16
1.5.1.2. Nursery Habitat 17
1.5.1.3. Adult Habitat 17
1.5.2. Identification and Distribution of Essential Habitat 17
1.5.3. Present Condition of Habitats and Essential Habitats 17
1.5.3.1. Quantity 17
1.5.3.2. Quality 18
1.5.3.3. Loss and Degradation 18
1.5.3.4. Current Threats 18
1.6. IMPACTS OF THE FISHERY MANAGEMENT PROGRAM 19
1.6.1. Biological and Environmental Impacts 19
1.6.2. Socioeconomic Impacts 20
2.0. GOALS AND OBJECTIVES 20
3.0. MANAGEMENT PROGRAM SPECIFICATIONS / ELEMENTS 21
3.1. ECOLOGICAL CONSIDERATIONS 21
3.2. ASSESSING ANNUAL RECRUITMENT 22
3.3. ASSESSING SPAWNING STOCK BIOMASS 22
3.4. ASSESSING MORTALITY 23
3.5. SUMMARY OF MONITORING PROGRAMS 23
3.6. BY-CATCH REDUCTION 25
3.7. HABITAT IMPACTS 25
4.0. MANAGEMENT PROGRAM IMPLEMENTATION 26
4.1. RECREATIONAL FISHERIES MANAGEMENT MEASURES 26
4.2. COMMERCIAL FISHERIES MANAGEMENT MEASURES 26
4.2.1. Management Measures for Bait Fisheries 26
4.2.2. Management Measures for Other Fisheries 29
4.2.3. Management Measures in Federal Waters 30
4.3. HABITAT CONSERVATION AND RESTORATION 30
4.4. ALTERNATIVE STATE MANAGEMENT REGIMES 30
4.4.1. Procedures 31
4.4.2. De minimis Status 31
4.5. ADAPTIVE MANAGEMENT 31
4.6. MANAGEMENT INSTITUTIONS 32
4.6.1. Atlantic States Marine Fisheries Commission
and ISFMP Policy Board 32
4.6.2. Management Board 32
4.6.3. Plan Review Team 32
4.6.4. Technical Committee 33
4.6.5. Stock Assessment Committee 33
4.6.6. Advisory Panel 33
4.6.7. Departments of Commerce and Interior 33
5.0. COMPLIANCE 33
5.1. MANDATORY COMPLIANCE ELEMENTS FOR STATES 33
5.1.1. Mandatory Elements of State Programs 34
5.1.1.1. Regulatory Requirements 34
5.1.1.2. Monitoring Requirements 34
5.1.1.3. Enforcement Requirements 34
5.1.2. State Reporting and Compliance Schedule 34
5.2. PROCEDURES FOR DETERMINING COMPLIANCE 35
6.0. MANAGEMENT RESEARCH NEEDS 37
6.1. STOCK ASSESSMENT AND POPULATION DYNAMICS 37
6.2. RESEARCH AND DATA NEEDS 37
7.0. REFERENCES 39
7.1. LITERATURE CITED 39
7.2. PERSONAL COMMUNICATIONS 44
HORSESHOE CRAB SPECIES PROFILE 47
LIST OF FIGURES, TABLES, AND APPENDICES
List of Figures
Figure 1. Format for biannual law enforcement reports. 36
List of Tables
Table 1. Current fishing regulations for horseshoe crabs by
State. 7
Table 2. Atlantic states landings for horseshoe crab for the
period 1970 - 1997. 12
Table 3. Reference period landings for commercial bait harvest
of horseshoe crabs between 1995 - 1997. 27
List of Appendices
Appendix A. Additional management options for bait fisheries
considered by the Management Board. 46
LIST OF ACRONYMS AND ABBREVIATIONS
ASMFC Atlantic States Marine Fisheries Commission
Board Horseshoe Crab Management Board
DNREC Delaware Department of Natural Resources and
Environmental Control
FDA U.S. Food and Drug Administration
Maryland DNR Maryland Department of Natural Resources
NMFS National Marine Fisheries Service
Plan Horseshoe Crab Fishery Management Plan
SAC Horseshoe Crab Stock Assessment Committee
USFWS U.S. Fish and Wildlife Service
1.0. STATUS OF THE HORSESHOE CRAB RESOURCE
1.1. INTRODUCTION
The Atlantic States Marine Fisheries Commission (ASMFC) develops
management plans for the various fishery resources within state
and federal waters. The ASMFC is a compact of the fifteen
Atlantic Coast states, created "to promote the better utilization
of the fisheries, marine, shell, and anadromous, of the Atlantic
seaboard by the development of a joint program for the promotion
and protections of such fisheries."
At its annual meeting in October 1997, the ASMFC voted to
initiate an independent fishery management plan for the horseshoe
crab (Limulus polyphemus). Initially, the ASMFC horseshoe crab
and the American eel (Anguilla rostrata) fishery management plans
were to be addressed in a single fishery management plan because
horseshoe crabs are used as a bait source in the eel pot fishery.
This draft Horseshoe Crab Fishery Management Plan (Plan) contains
discussions of horseshoe crab life history, the ecological
significance of the horseshoe crab, the problems associated with
the species' possible decline, status of stocks, and current
fisheries including biomedical use. This Plan also identifies
the condition of existing horseshoe crab habitat and its current
threats. Finally, this Plan identifies management, monitoring,
and information needs to ensure the continued role of the
horseshoe crab resource in the ecology of coastal ecosystems,
while providing the opportunity for commercial, recreational,
medical, scientific, and educational use over time. A species
profile is provided in an appendix of the Plan.
1.1.1. Statement of the Problem
The status of horseshoe crab populations along the Atlantic
Seaboard is poorly understood and is based on independent
spawning surveys, egg counts, and trawl surveys, primarily
conducted in the Delaware Bay region. Concern over increased
exploitation of horseshoe crabs, particularly in the mid-Atlantic
States, has been expressed by state and federal fishery resource
agencies, conservation organizations, and fisheries interests.
Horseshoe crabs are important to migrating shorebirds and
federally listed sea turtles as sources of food, and are critical
to biomedical research and pharmaceutical testing. Because
horseshoe crabs are slow to mature and easily harvested with
minimal financial investments, populations are sensitive to
harvest pressure.
Upon completion and approval of a management plan, ASMFC states
are obliged to implement its mandatory requirements. If a state
does not comply with the mandatory measures of the ASMFC fishery
management plan, the law allows the U.S. Secretary of Commerce to
impose a moratorium in that state's particular fishery. All
ASMFC fishery management plans must include specific measurable
standards to improve the status of the stocks and to determine
the state's compliance with those standards.
1.1.2. Benefits of Implementation
The purpose of a comprehensive horseshoe crab fishery management
plan for the Atlantic states and adjacent federal waters is to
provide consistent management and regulation for both the long-
term viability of the horseshoe crab resource and use of the
resource by current and future generations of the fishing and non-
fishing public. Current management strategies implemented by
various states (e.g., New Hampshire, New Jersey, Delaware,
Maryland, and Virginia) provide piecemeal efforts in protecting
the horseshoe crab resource. These current state management
practices have not been coordinated and cannot control the
substantial harvest that may occur in "unregulated" federal
waters. A coordinated and consistent management strategy
throughout state and federal waters along the Atlantic Coast
would help promote the long-term viability of horseshoe crab
populations.
Implementing a coastwide fishery management plan would benefit
commercial fisheries, such as the American eel and conch (Busycon
carica and B. canaliculatum) fisheries, by providing the long-
term supply of a bait source. Successful management also may
avoid future harvest moratoriums as experienced in New Jersey
during 1997 and piecemeal harvest reduction measures as
experienced in New Jersey, Delaware, and Maryland in 1998. A
management strategy also would benefit dependent fish and
wildlife resources, such as shorebirds and the federally listed
(threatened) loggerhead turtle (Caretta caretta), by ensuring a
readily available and continuing supply of adult horseshoe crabs
and horseshoe crab eggs. However, overprotection of horseshoe
crabs could adversely impact surf clam (Spisula solidissima)
resources via heavy predation by horseshoe crabs on surf clam
seed beds. Also, management will ensure an essential and
adequate supply of horseshoe crabs for the biomedical industry.
The use of horseshoe crab blood is critical in testing
pharmaceutical drugs and equipment for bacterial contamination.
1.2. DESCRIPTION OF THE RESOURCE
The horseshoe crab life history was developed from available
scientific literature and state natural resource agency documents
and is intended to provide the reader with the basic information
to understand the life cycle and habitat requirements of
horseshoe crabs. Additional information is provided in the
Species Profile section of the plan.
There is currently no available stock assessment review of
horseshoe crabs along the Atlantic Coast. As a result, stock
assessment summaries are based on scientific literature and
existing resource data collected during independent spawning
surveys, trawl, and egg count surveys. The Horseshoe Crab Stock
Assessment Committee reviewed and summarized the available data
in a report. The Committee concluded that the horseshoe crab
population in the mid-Atlantic region has remained stable in
recent years, while reported commercial landings data show a
substantial increase in harvest during the 1990s (Atlantic States
Marine Fisheries Commission, 1998). The Stock Assessment
Committee commented that the Delaware trawl survey shows a
decreasing abundance trend between 1990 and 1997. The Stock
Assessment Committee also identified that many of the surveys
collecting information on horseshoe crabs have significant design
inadequacies.
1.2.1. Species Life History
Horseshoe crabs are benthic (or bottom-dwelling) arthropods that
use both estuarine and continental shelf habitats. Although it
is called a "crab," it is neither a decopod or crustacean, rather
horseshoe crabs are grouped in their own class (Merostomata),
which is more closely related to the arachnids. Horseshoe crabs,
ranging from the Yucatan peninsula to northern Maine, are most
abundant between Virginia and New Jersey, with the largest
population of spawning horseshoe crabs in the world found in the
Delaware Bay (Shuster, pers. comm., 1995). While adult horseshoe
crabs have been found as far as 35 miles offshore, 74 percent of
the horseshoe crabs caught in bottom trawl surveys conducted by
the National Marine Fisheries Service (NMFS), Northeast Fisheries
Center were taken in water shallower than 20 meters (Botton and
Ropes, 1987a). Horseshoe crabs are ecological generalists and
can survive within a wide range of environmental conditions.
Studies suggest that each spring, adult horseshoe crabs migrate
from deep bay waters and the Atlantic continental shelf to spawn
on intertidal sandy beaches. Beaches within estuaries, such as
the Delaware and Chesapeake Bay, are preferred because they are
low energy environments and are protected from the surf, thus
reducing the risks of stranding during spawning events. Spawning
generally occurs from March through July, with the peak spawning
activity occurring on the evening new and full moon high tides in
May and June (Shuster and Botton, 1985). In the Delaware Bay and
the Chesapeake Bay, spawning activity gradually increases prior
to the full and new moon, peaking on the day of the full and new
moon, then gradually decreases (Maio, et al., 1998; Maryland
Department of Natural Resources, 1998). However, in the
Chesapeake Bay, peak horseshoe crab spawning does not occur
consistently on any one day around the full and new moons
(Maryland Department of Natural Resources, 1998). In South
Carolina, spawning occurs from March to July, with peak spawning
in May during night high tides greater than 6.0 feet above mean
high water (Thompson, 1998). In Florida, spawning occurs between
March and November, with peak spawning occurring between mid-June
and the end of August (Rudloe, 1980).
Horseshoe crabs are characterized by high fecundity, high egg and
larval mortality, and low adult mortality (Botton and Loveland,
1989; Loveland et al., 1996). Horseshoe crabs spawn multiple
times per season, laying approximately 3,650 to 4,000 eggs in a
cluster. Adult females lay an estimated 88,000 eggs annually
(Shuster, 1982). Egg development is dependent on temperature,
moisture, and oxygen content of the nest environment.
Eggs hatch between 14 and 30 days after fertilization (Sekiguchi,
et al., 1982; Jegla and Costlow, 1982; Botton, 1995). Survival
between hatching and sexual maturity remains unknown. Loveland
et al. (1996) identify that egg and larval mortality is
substantial, primarily due to predation. Some "trilobite" larvae
delay emergence and overwinter within beach sediments, emerging
the following spring (Botton et al., 1992). Larvae typically
settle in shallow water areas to molt (Shuster, 1982). Juvenile
horseshoe crabs generally spend their first and second summer on
the intertidal flats, usually near breeding beaches (Shuster,
1982). Older individuals move out of intertidal areas to a few
miles offshore, except during breeding migrations (Botton and
Ropes 1987a). However, some adult horseshoe crabs reside in the
coastal bays year-round (O'Connell, pers. comm., 1997). The
horseshoe crab must molt or shed its chitinous exoskeleton to
grow. Molting occurs several times during the first two to three
years. As the horseshoe crab grows larger, there are longer
periods between molts. Horseshoe crabs molt at least 16 to 17
times over 9 to 11 years to reach sexual maturity (Shuster,
1950). Based on growth of epifaunal slipper shells (Crepidula
fornicata) on their prosoma, horseshoe crabs live at least 17 to
19 years in the northern part of their range, (Botton and Ropes,
1988).
Larvae feed on a variety of small polychaetes and nematodes
(Shuster, 1982). Juvenile and adult horseshoe crabs feed mainly
on molluscs including razor clam (Ensis spp.), macoma clam
(Macoma spp.), surf clam (Spisula solidissima), blue mussel
(Mytilus edulis), wedge clam (Tellina spp.), and fragile razor
clam (Siliqua costata). Horseshoe crabs also prey on a wide
variety of benthic organisms including arthropods, annelids, and
nemertean worms (Botton, 1984a; Botton and Haskin, 1984). Botton
(1984a) also found vascular plant material in nearly 90 percent
of all individuals.
Factors contributing to natural mortality include age; excessive
energy expenditure during spawning, which can result in
stranding, desiccation, and predation. Loveland et al. (1996)
believe that the natural mortality rate in adults is probably
low. However, horseshoe crab mortality due to predation from sea
turtles and other marine animals remains unknown. Shorebirds
feed on horseshoe crab eggs in areas of high spawning densities
such as the Delaware Bay. Horseshoe crab eggs are considered
essential food for several shorebird species in the Delaware Bay,
which is the second largest migratory staging area for shorebirds
in North America. Despite significant shorebird predation on
horseshoe crab eggs, such activity probably has little impact on
the horseshoe crab population (Botton et al., 1994). Horseshoe
crabs place egg clusters at depths greater than 10 centimeters,
which is deeper than most short-billed shorebirds can penetrate.
Many eggs are brought to the surface by wave action and burrowing
activity by spawning horseshoe crabs. These surface eggs
consumed by birds would not survive, due to desiccation (Botton
et al., 1994). A significant decrease in the number of horseshoe
crabs could leave a large portion of migrating shorebirds without
necessary food resources to complete migration and successfully
reproduce on arctic breeding grounds.
Adult and juvenile horseshoe crabs make up a portion of the
loggerhead sea turtle's (Caretta caretta) diet in the Chesapeake
Bay (Musick, et al. 1983). Horseshoe crab eggs and larvae are
also a seasonally preferred food item of a variety of
invertebrates and finfish, including sharks (Squaliformes)
(Shuster, 1982).
Human activity probably accounts for the greatest proportion of
adult horseshoe crab mortality. Between the 1850s and the 1920s,
over one million horseshoe crabs (4 million pounds using a
conversion rate of 4 pounds / individual) were harvested annually
for fertilizer and livestock feed (Shuster, 1982; Shuster and
Botton, 1985). Shuster (1996) reports harvest in the 1870s of
over four million horseshoe crabs per year (16 million pounds).
More recently horseshoe crabs have been taken in substantial
numbers (e.g., over 5 million pounds in 1996) to provide bait for
other fisheries, including (primarily) the American eel and conch
fisheries. Horseshoe crabs, particularly females, are sectioned
and placed in American eel pots as bait. The conch fishery uses
horseshoe crabs of either sex. Horseshoe crabs are collected by
the biomedical industry to produce Limulus Amebocyte Lysate.
This industry bleeds individuals and releases the animals live
after the bleeding procedure. Two studies estimate 10 to 15
percent of animals do not survive the bleeding procedure (Rudloe,
1983; Thompson, 1998). Entrapment in or by man-made structures,
such as rip-rap, bulkheads, revetments, jetties, and stationary
fishing devices, may account for additional mortality.
1.2.2. Stock Assessment Summary
The status of horseshoe crab populations along the Atlantic
Seaboard is poorly understood due to the limited amount of
information collected regarding stock levels. In addition, basic
information regarding age and growth rates, recruitment, and
population dynamics is lacking. Other than the NMFS trawl survey
data, little information was collected until the late 1980s when
independent spawning surveys and trawl surveys were initiated,
primarily in the Delaware Bay region. However, the NMFS trawl
survey data is confounded by a gear change and the location of
the survey areas (i.e., surveys were not conducted in shallow
waters). Concern over perceived growing exploitation of
horseshoe crab has been expressed by state and federal fishery
resource agencies, conservation organizations and fisheries
interests.
1.2.2.1. Distribution
Horseshoe crabs, ranging from the Yucatan Peninsula to Maine, are
most abundant between Virginia and New Jersey (Shuster, 1982).
In New Jersey and Delaware, horseshoe crab abundance decreases
with distance north and south of the Delaware Bay (Botton and
Haskin, 1984). Within the Delaware Bay, the largest concentration
of horseshoe crabs traditionally was found along the Cape May
shore of New Jersey (Shuster and Botton, 1985). Spawning
densities of over 30 animals per meter occurred on the New Jersey
side of the Delaware Bay based on 1986 spawning counts along 15
meter segments (Botton, et al., 1988). Since 1993, the majority
of horseshoe crab spawning activity has occurred on the Delaware
shores of the Delaware Bay (Swan, unpublished data, 1998).
Annual variation in spawning concentrations may be the result of
weather or habitat changes. In the Chesapeake Bay, spawning
densities only exceed one per meter on the most heavily used
beaches, based on counts using similar methodology. During peak
spawning, densities exceeded three per meter on these preferred
beaches (Maryland Department of Natural Resources, 1998). Rudloe
(1980) and Thompson (1998) reported spawning densities in Florida
and South Carolina as three and one animal per meter,
respectively.
1.2.2.2. Sex and Age Ratio
Sex ratios at spawning beaches have been reported by Rudloe
(1980) in Florida to range from 1 to 14 males per female with a
mean of 3.6 males per female. Limuli Laboratories' annual census
reports sex ratios in New Jersey and Delaware averaging 2.8 male
per female between 1990 and 1995 (Swan, pers. comm., 1998).
Shuster and Botton (1985) report sex ratios on spawning beaches
in New Jersey and Delaware varying between 5:1 and 3:1 (male :
female). Thompson (1998) reported average sex ratios on spawning
beaches in South Carolina of 3.5:1. Barlow et al. (1986) found
sex ratios of 2.5:1 in Massachusetts in 1986. Maryland
Department of Natural Resources (1998) reported a 2:1 sex ratio
in 1994 and 1995, based on spawning surveys. The sex ratio in
1996 and 1997 was 4:1 (Maryland Department of Natural Resources,
1998). However, the sex ratio cannot be ascertained readily from
spawning counts because the mating behavior of the males is to
concentrate along the shoreline, whereas females generally move
into deeper water after spawning (Shuster, 1996). The abundance
of males may be an adaptation to favor genetic diversity and to
maximize fertilization, because fertilization is external and
males compete to fertilize eggs (Brockmann, 1990; Shuster, 1996).
Offshore trawl collections indicate a reversed sex ratio, with
females outnumbering males from 3:2 to 2:1 (Rudloe, 1980) or an
even sex ratio 1.17 males per female (Swan et al., 1993). The
New Jersey Division of Fish, Game and Wildlife (1997) identified
a female dominated sex ratio of 1:1.4 based on 1996 trawl
surveys. Rudloe (1980) and Thompson (1998) concluded that the
overall sex ratio may be 1:1.
Shuster (1996) suggested that a shift in the normal 1:1 sex ratio
toward less than one female per male becomes an important
criterion, pointing specifically to overfishing of females. In
South Carolina, the 1997 male to female ratio was higher for each
estuary sampled than the preceding years (i.e., 1996 and 1995)
(Thompson, 1998), indicating a population changing due to
environmental conditions or overharvesting. Trawling in the
Delaware Bay by the Delaware Division of Fish and Wildlife (1997)
identified annual sex ratios of approximately 1:1 for 1990
through 1996, except in 1993 and 1994 when 1.6:1 was noted
(significant at (p<0.05) from 1:1).
1.2.2.3. Stock Assessment
Horseshoe crab population data have been collected by the NMFS
and state trawl surveys, egg count surveys, and spawning surveys.
State trawl surveys include trawl surveys in Massachusetts, the
Peconic Bay small mesh trawl survey in New York, the New Jersey
Ocean Stock Assessment Program coastal nearshore trawl survey,
the 30-foot otter trawl and 16-foot otter trawl surveys in
Delaware, the coastal bays trawl survey in Maryland, and the
South Carolina Department of Natural Resource's Crustacean
Management Section trawl survey. The NMFS / Northeast Fisheries
Science Center conducts an Atlantic Coast trawl survey (spring
and fall) between Maine and North Carolina. Egg counts were
conducted by Dr. Robert Loveland and Dr. Mark Botton in New
Jersey based on the total number of eggs / standardized core
within the upper layer of the substrate (0-5 cm) and the lower
layer of the substrate (15-20 cm). Several spawning surveys have
been conducted in the mid-Atlantic Bight including the Delaware
Bay spawning survey (coordinated by Limuli Laboratories), the
State of Maryland spawning surveys, and spawning surveys
conducted by Maio et al. (1998) in Maryland. The State of New
Jersey conducts a surf clam survey along the Atlantic Coast of
New Jersey using a commercial hydraulic clam dredge with a 72-
inch knife. Tagging data are collected in New Jersey, Maryland,
and South Carolina. The sample areas, design methodology, and
survey time series vary among data sets.
The Horseshoe Crab Stock Assessment Committee (SAC) of the ASMFC
reviewed existing horseshoe crab population and harvest data.
The SAC summarized the available data in a report and concluded
that the horseshoe crab population in the mid-Atlantic region has
remained stable in recent years (Atlantic States Marine Fisheries
Commission, 1998). Recent (no earlier than 1985 to present) data
from four state and two federal trawl surveys show no increasing
or decreasing trend in horseshoe crab abundance (Atlantic States
Marine Fisheries Commission, 1998). The SAC noted that the
Delaware trawl survey shows a decreasing abundance trend between
1990 and 1997. A high correlation was found between the Delaware
trawl survey and the Delaware Bay beach spawning count survey,
lending more credence to the evidence for a decline. However,
this information is confounded by a short time-series (1990-1997)
and potential shifts in spawning habitat (Atlantic States Marine
Fisheries Commission, 1998). The SAC also identified a decrease
in egg abundance on New Jersey beaches of the Delaware Bay
between 1990-1991 and 1996-1997. The lack of a similar study on
Delaware beaches of the Delaware Bay coupled with the short time-
series and uncertainty in the reason for the decline in egg
abundance led to the SAC's decision not to use the results of
this survey in the current stock assessment (Atlantic States
Marine Fisheries Commission, 1998). However, the SAC suggested
further investigating the egg count survey as a means to monitor
the horseshoe crab population.
Additional information regarding available population and harvest
data and the SAC review is provided in the SAC report (Atlantic
States Marine Fisheries Commission, 1998). The Horseshoe Crab
Technical Committee's review of the SAC report reiterated that
many of the data sets evaluated may not be sensitive enough to
determine trends and concluded that the horseshoe crab population
in the mid-Atlantic region is either stable or declining. The
Horseshoe Crab Technical Committee recommended that an
independent review of the SAC report is necessary and that
further evaluation of egg count data is required.
1.3. DESCRIPTION OF THE FISHERY
Fishing effort for horseshoe crabs is generally concentrated
within the mid-Atlantic area, specifically New Jersey, Delaware,
Maryland, Virginia, and adjacent federal waters. Since there is
no known recreational fishery for horseshoe crabs, fishing
mortality of horseshoe crabs is predominantly from the commercial
fisheries including the bait fishery and the biomedical fishery.
1.3.1. Current Fishery Regulations
Current fishing regulations vary dramatically among the Atlantic
coastal states. Generally, fishing regulations for horseshoe
crabs are minimal or nonexistent in comparison with other
fisheries (Table 1). However, several states (e.g., New
Hampshire, New Jersey, Delaware, Maryland, and Virginia) have
recently initiated or proposed more restrictive harvest
regulations. The State of South Carolina has prohibited harvest
except for the biomedical industry since 1991.
1.3.2. Commercial Fishery
Between the 1850s and the 1920s, over 1 million horseshoe crabs
were harvested annually for fertilizer and livestock feed
(Shuster, 1982; Shuster and Botton, 1985). Reported harvests in
the 1870s were 4 million horseshoe crabs annually, and 1.5 to 1.8
million horseshoe crabs annually between 1880s and 1920s (Finn et
al., 1991). Shuster (1960) reports that in the late 1920s and
early 1930s 4 to 5 million crabs were harvested annually.
Shuster (1960) reports over 1 million crabs were harvested during
the 1940s and 500,000 to 250,000 horseshoe crabs were harvested
in the 1950s. By the 1960s, only 42,000 horseshoe crabs were
reported to be harvested annually (Finn et al., 1991). Early
harvest records are suspect due to under-reporting. The period
of time between 1950 and 1960 is considered the nadir of
horseshoe crab abundance. The substantial commercial-scale
harvesting of horseshoe crabs ceased in the 1960s (Shuster,
1996).
1.3.2.1. Bait Fishery
Currently, horseshoe crabs are commercially harvested for use as
American eel, conch (or whelk), and catfish bait along certain
portions of the Atlantic coast. The horseshoe crab fishery is
unique in that crabs can be easily harvested during their
spawning season and can be caught with a minimal financial
expense. The eel fishery is highly dependent on sustained
populations of horseshoe crabs and prefers female horseshoe crabs
with eggs. The conch fishery also is dependent on horseshoe
crabs, but uses both male and female horseshoe crabs.
Table 1. Current fishing regulations for horseshoe crabs by
State.
---------------------------------
State Regulations
---------------------------------
MAINE No regulations regarding harvest (Sorksen,
pers. comm., 1997).
NEW HAMPSHIRE Possession limit of 10 per day per person.
License required to sell or distribute and
mandatory monthly reporting is required (Nelson,
pers. comm., 1997).
RHODE ISLAND No regulations regarding harvest; however, to sell
commercially, a commercial fishing license is
required ($200/year). A moratorium on commercial
licenses is currently in place (Sisson, pers.
comm., 1997).
MASSACHUSETTS No regulations regarding harvest; however, to sell
commercially, a commercial fishing license is
required ($65/year-residents, $130/year-
nonresidents) (Coates, pers. comm., 1997).
CONNECTICUT No regulations regarding harvest (Babey, pers.
comm., 1997).
NEW YORK No regulations regarding harvest; however, to
sell commercially, or to take and land more than
50, a license is required ($30/year-residents,
$50/year-nonresidents (Colvin, pers. comm., 1997).
NEW JERSEY Harvest requires a horseshoe crab permit and
mandatory monthly reporting. The following
persons are exempt from obtaining a permit: (1)
property owners removing dead horseshoe crabs from
their property for the purpose of disposal, (2)
scientific collection with appropriate scientific
collecting permit, and (3) individuals in
possession of a miniature fyke, lobster, or fish
pot license and written verification that
horseshoe crabs were obtained from a legal source.
In order to qualify for a horseshoe crab permit,
individuals must have had a miniature fyke,
lobster, or fish pot license; a horseshoe crab
permit; and reported landings for at least 2 years
between 1993 and 1997. Harvest by any other means
than by hand (i.e., trawling or dredging) is
prohibited. Harvest season is April 1 to August
15. No harvest is allowed from the beaches and
shoreline and the adjacent waters and uplands
within 1,000 feet of mean high water along the
Delaware Bay. Hand-harvest is permitted in areas
other than the abovementioned areas only two days
/ week (Tuesday and Thursday) (Himchak, pers.
comm., 1997).
PENNSYLVANIA No regulations regarding harvest (Snyder, pers.
comm., 1998).
Table 1. (continued)
---------------------------------
State Regulations
---------------------------------
DELAWARE No collection on State or federal land
(horseshoe crab sanctuaries) between May 1 and
June 30, except Tuesdays and Thursdays on state
owned lands east of State Road Number 89 by
persons with valid horseshoe crab collecting
permits or American eel licenses. No collection
on private land between May 1 and June 30 except
permittees on Monday, Wednesday, and Friday.
Hand harvest by persons with valid commercial eel
fishing licenses requires mandatory reporting and
horseshoe crabs must be for personal, non-
commercial use. Dredging is prohibited in leased
shellfish grounds except on one's own leased
shellfish grounds or with permission from the
owner of leased shellfish grounds. Harvest by
vessels is limited to 1,500 horseshoe crabs / 24
hours. Harvest by dredging is prohibited between
May 1 and June 30. Trawling is prohibited in
State waters. Monthly reporting is required by
all permittees. Containment or transport of more
than 300 cubic feet of space occupied by horseshoe
crabs is prohibited. Permittees must have secured
at least 2 valid horseshoe crab collecting permits
from previous years. If collecting permits drops
to 45 or below, a lottery will be held to increase
commercial collecting permits to 50. Permit fees
are $100/year-resident and $1,000/year-non-
resident (Manus, pers. comm., 1998).
MARYLAND The annual total allowable landings of
horseshoe crabs for the commercial fishery is
750,000 pounds. Harvest requires a horseshoe crab
catch and landing permit. In order to qualify for
a permit, a person must be licensed in accordance
with Natural Resources Article S4-701, Annotated
Code of Maryland and reported catching and landing
horseshoe crabs in Maryland during 1996. A person
may not catch or land horseshoe crabs in Maryland
between December 1 and March 31. A person may not
catch horseshoe crabs within 1 mile of the
Atlantic Coast, Chesapeake Bay and coastal bays
from April 1 through June 30. A person may catch
and land horseshoe crabs on Monday through Friday
from outside of 1 mile of the Atlantic Coast
between April 1 and June 30 in accordance to the
following catch limits: (1) 100 horseshoe crabs
for a permittee; and (2) 25 horseshoe crabs for a
non-permittee. A person may catch and land
horseshoe crabs on Monday through Friday from the
tidal waters of the State between July 1 and
November 30 in accordance to the following catch
limits: (1) the daily catch limit for permittees
shall be based on the ratio of landings for 1996
as applied to the annual total allowable landings
for the present year; and (2) 25 horseshoe crabs
for a non-permittee. A person who catches and
lands horseshoe crabs in Maryland shall report
catch and landing information on the forms
provided by the Department. A person authorized
to catch and release horseshoe crabs for purposes
of scientific research shall be exempt from these
regulations, but must return the horseshoe crabs
live within 48 hours to the waters from which the
horseshoe crabs were taken (O'Connell, pers.
comm., 1998).
VIRGINIA Harvest by means of trawling or dredging is
prohibited. However, special scientific
collection permits have been issued to trawler to
catch horseshoe crabs for medical purposes.
License required to hand-harvest ($15/year) in
addition, to obtain a license the applicant must
be a registered waterman ($150/year). No limits
for hand-harvesting (Travelstead, pers. comm.,
1997).
Table 1. (continued)
---------------------------------
State Regulations
---------------------------------
NORTH CAROLINA No regulations regarding harvest (Daniel, pers.
comm., 1997).
SOUTH CAROLINA Special permits required for harvest and / or
possession. Harvest of horseshoe crabs is limited
to biomedical industry (production of LAL) and to
scientific, educational, or commercial display.
Harvesting vessels must be properly licensed in
addition to being permitted. Permits may be
conditioned as to lawful fishing areas; minimum
size requirements for horseshoe crabs; mesh size
and dimensions of nets and other harvesting
devices; by-catch provisions; fishing times or
periods; catch reporting requirements; holding
facilities, conditions, and periods; and any other
conditions the State determines appropriate.
Horseshoe crabs harvested for LAL production must
be returned unharmed to State waters of comparable
salinity and water quality after they are bled.
Penalties for violating permit conditions, upon
conviction, may include monetary fines, suspension
or revocation of the permit(s), and seizure and
sale of the permittee's vessel (Cupka, pers.
comm., 1998).
GEORGIA No regulations regarding harvest; however,
experimental fishing contract may be required for
significant commercial fishery activities (Evans,
pers. comm., 1997).
FLORIDA No regulations regarding harvest; however, to
sell commercially, a salt-water products license
is required ($50/year-residents) (Vale, pers.
comm., 1997).
FEDERAL WATERS No regulations regarding harvest (Maney, pers.
comm., 1997).
---------------------------------
Commercial landings data for horseshoe crabs (i.e., metric tons,
pounds, and price) are collected by the NMFS by state, year, and
gear type. Commercial landings data may include harvest for both
the bait and biomedical fisheries. However, the NMFS data are
relatively incomplete and disjunct. For example, in several
years that NMFS reports no landings in states such as Delaware,
state biologists report that landings did occur (Michels, pers.
comm., 1997). In 1994 and 1995, the NMFS reported Maryland's
harvest at 232,000 and 117,000 pounds, respectively. Based on
State landing records, actual Maryland harvest was approximately
1 million pounds during these years (O'Connell, pers. comm.,
1998). In many cases, horseshoe crabs are harvested and used
directly by eel fishers, whelk fishers, or catfish fishers
without going through a dealer (where NMFS gets much of its
information) or arrangements are made for harvesters to sell
directly to such fisheries without going to dealers. Since such
private sales are not reported, NMFS fishery statistics
underestimate the catch. Based on NMFS data, commercial harvest
from the northeastern Atlantic coast has ranged between 10,000
pounds (in 1969) to over 5.0 million pounds (in 1996) (National
Marine Fisheries Service, 1998). Since 1988, commercial landings
have averaged 1,436,808 pounds. Botton and Ropes (1987b)
estimated the total number of horseshoe crabs harvested by
comparing the total number of pounds landed with the average
weight of an adult horseshoe crab, which is approximately 4
pounds. However, the NMFS used a different conversion factor to
estimate the number of pounds landed (e.g., 2.6 pounds per crab).
The total average horseshoe crab catch (animals/year) for the
Atlantic Coast (assuming an adult horseshoe crab is 4 pounds) has
increased from 476,515 in 1993 to 1,288,408 in 1996 (National
Marine Fisheries Service, 1998). This increase is similar to
increases reported by Michels (unpublished data, 1997) for the
Delaware Bay harvest, which ranged from 330,333 in 1993 to
896,540 in 1996. However, Michels (unpublished data, 1997) did
not include the Maryland harvest (which can be substantial).
These statistics provide further evidence that the NMFS data
represent an underestimate of actual harvest. Regardless of the
data set used, all data show a significant increase in harvest
between 1990 and 1996.
The SAC concluded in its report that commercial landings data
show a substantial increase in reported harvest during the 1990s
(Atlantic States Marine Fisheries Commission, 1998). This
increase could be, in part, a function of increased harvest
reporting efficiency. The states of Delaware, Maryland, New
Jersey, and New York represent the largest harvest of horseshoe
crabs recently. Estimates in Delaware, Maryland, New Jersey, New
York, and Rhode Island indicate a rapid increase in fishery
growth, based primarily on use as bait for the American eel and
whelk fisheries and the shift in pressure from declining
traditional fisheries (Michels, unpublished data, 1997; National
Marine Fisheries Service, 1998; Thompson, 1998). However, the
states of Connecticut, Massachusetts, North Carolina, and
Virginia indicate declines in current harvest compared with
harvest in the late 1970s and early 1980s (National Marine
Fisheries Service, 1998).
Based on reported landings in New Jersey alone, horseshoe crab
harvests have increased in the last three years from
approximately 250,000 in 1993 to over 600,800 in 1996. The
Delaware Division of Fish and Wildlife (1997) reports increases
in landings between 1990 (under 250,000 pounds) and 1997 (over
1,500,000 pounds). The Delaware Division of Fish and Wildlife
(1997) also reports increases in effort as represented by
issuance of beach collection permits, which increased from 18 in
1991 to 131 in 1997. However, prior to 1991 little or no
reporting occurred within the Delaware Bay. Thus, the increase
in horseshoe crab harvest during the 1990s may be partly related
to mandatory reporting requirements.
Primary harvest was identified in Rhode Island, New Jersey,
Delaware, Maryland, and Virginia. Little to no harvesting of
horseshoe crabs was reported in Maine, New Hampshire, or
Connecticut (Botton and Ropes, 1987b). The Chesapeake Bay in
Maryland and Virginia likely has a substantial harvest, but
without quantitative studies, the catch remains under-reported.
Maryland has been responsible for 23 to 78 percent of the total
commercial catch of horseshoe crabs from the northeastern
Atlantic coast since 1980 (National Marine Fisheries Service,
1998). Maryland averaged 357,000 pounds between 1981 and 1991
from a small directed ocean fishery and by-catch from the clam
fishery. Since 1992, harvest has increased significantly in
Maryland with 2.6 million pounds landed in 1996. Maryland's
fishery is primarily an offshore trawl fishery; more than 95
percent of the harvest occurs from July through November. In
1996, 96 percent of Maryland's harvest was from waters outside of
1 mile (52 percent from State waters [1-3 miles] and 44 percent
from federal waters [3+ miles]), 3 percent from the coastal bays,
and <1 percent from the Chesapeake Bay (O'Connell, pers. comm.,
1998).
In Virginia, horseshoe crab harvest averaged 190,000 pounds
between 1980 and 1988. With a ban on trawling in state waters
since 1989, horseshoe crab landings have decreased considerably,
averaging 22,000 pounds (Butowski, 1994) and only increasing to
86,294 pounds in 1996 (National Marine Fisheries Service, 1998).
Demand has increased in Virginia as indicated by whelk landings,
which have increased from 75,000 pounds in 1994 to 750,000 pounds
in 1995 (Petrocci, 1997).
Reported dockside value from the northeastern Atlantic coast has
ranged between $289 (1967) and $1,541,260 (1996). Fishery
statistics (Table 2) for the period 1970 through 1995 indicate a
variable fishery. As previously identified, fishery statistics
probably underestimate the catch of horseshoe crabs, because the
sale of crabs for bait is often arranged between private
individuals (i.e., unreported in NMFS landing statistics) rather
than through centralized dealers (Botton and Ropes 1987b).
In 1997, the majority (85 percent) of horseshoe crabs in Delaware
were landed by hand harvest, while dredge harvest made up
approximately 15 percent (Delaware Division of Fish and Wildlife,
1997). Between 1991 and 1996 the majority of the horseshoe crabs
were landed by hand-harvest (63 percent) compared to dredging (37
percent) (Delaware Division of Fish and Wildlife, 1997), except
for 1991 when the dredge harvest dominated the catch (56
percent). The increased harvest noted in Delaware mirrored
increases in the number of hand-collection permits issued
(Delaware Division of Fish and Wildlife, 1997). National Marine
Fisheries Service data compiled by Delaware Division of Fish and
Wildlife (1997) identified that among the northeastern and mid-
Atlantic States, Maryland, New Jersey, and Delaware harvest the
majority of horseshoe crabs (36, 31, and 14 percent,
respectively).
The shrimp trawl fishery in the South Atlantic Bight may
contribute to horseshoe crab mortality via by-catch (Thompson,
1998), but the amount of by-catch harvest remains unreported.
The amount of horseshoe crab by-catch has become very small,
since the use of turtle excluder devices became mandatory in the
shrimp trawl fishery (Cupka, pers. comm., 1998).
1.3.2.2. Biomedical Fishery
Scientists have used horseshoe crabs in eye research, surgical
sutures wound dressing development, and detection of bacterial
endotoxins in drugs and intravenous devices (Hall, 1992).
Limulus Amoebocyte Lysate (LAL), a clotting agent in horseshoe
crab blood, has made it possible to detect human pathogens such
as spinal meningitis and gonorrhea in patients, drugs, and all
intravenous devices. In 1964, researchers discovered that
horseshoe crab blood coagulates in the presence of minute
quantities of gram-negative bacterial endotoxin and the LAL
industry was initiated. By 1979, the U.S. Food and Drug
Administration (FDA) issued draft guidelines for the use of LAL
as an end-product pyrogen test for endotoxin in medical devices
and injectable drugs. The LAL test is currently the worldwide
standard for screening medical equipment for bacterial
contamination; any drug produced by a pharmaceutical company must
pass an LAL screening. No other known procedure has the same
accuracy as the LAL test. If LAL became unavailable, it could
take years to find a universally accepted replacement. To obtain
LAL, manufacturing companies catch primarily adult horseshoe
crabs, collect a portion of their blood, and then release them
alive.
Table 2. Atlantic states landings for horseshoe crab for the
period 1970 - 1997.
---------------------------------
ATLANTIC STATES LANDINGS (MAINE - FLORIDA)
Year Pounds Value
(in $1000s)
---------------------------------
1970 15,900 7.79
1971 11,900 3.01
1972 42,000 2.63
1973 88,700 5.54
1974 16,700 6.90
1975 62,800 18.90
1976 2,043,100 63.96
1977 473,000 16.58
1978 728,500 45.59
1979 1,215,630 148.24
1980 566,447 79.02
1981 326,695 55.97
1982 510,060 44.95
1983 440,959 35.83
1984 152,392 15.36
1985 522,199 41.46
1986 507,814 47.82
1987 462,663 67.82
1988 636,252 71.23
1989 1,087,912 131.72
1990 908,130 101.81
1991 1,089,045 121.50
1992 1,000,619 109.71
1993 1,906,059 207.22
1994 1,401,656 228.60
1995 2,547,987 378.99
1996 5,153,630 1541.26
1997 1,885,883 334.44
---------------------------------
Source: National Marine Fisheries Service (1998)
Note: All dollars are 1992 dollars, adjusted by the implicit
price deflator (GDP). All life stages are included.
In 1989, the FDA reported that 130,000 horseshoe crabs were used
in the biomedical industry. The current estimate of medical
usage is between 200,000 and 250,000 horseshoe crabs per year on
the Atlantic Coast (Swan, pers. comm., 1998; McCormick, pers.
comm., 1998). The FDA mandates conservation by requiring the
return of horseshoe crabs to the environment. Most labs return
bled crabs to their habitat within 72 hours of capture, but may
or may not release crabs at the collection site (Botton, 1995).
Approximately 10 percent of the crabs do not survive the bleeding
procedure, which comprises a source of mortality that is not
included in the commercial catch statistics (Rudloe, 1983).
Based on a tagging and controlled mortality study, Thompson
(1998) reported similar post-processing mortality of horseshoe
crabs (10 to 15 percent). Mortality due to the bleeding
procedure may be lower (e.g., 0 to 4 percent), depending on the
biomedical facility (Swan, pers. comm., 1998), but the mortality
associated with collection, shipping, and handling remains
unknown. This mortality is minimal compared to that from the
commercial bait fishery.
In South Carolina, live horseshoe crabs may be taken only for use
in LAL production, with animals returned to natural habitat after
bleeding. Landings in South Carolina by hand-harvest and trawl
has increased since the late 1980s. The annual reported harvest
in South Carolina has increased over 300 percent since reporting
requirements were established in 1991 (Thompson, 1998).
Presumably, this increase in harvest was driven by the
biomedical industry's demand for more horseshoe crabs.
Horseshoe crabs are used also to make chitin filament for
suturing (Hall, 1992). Since the mid-1950s medical researchers
have known that chitin-coated suture material enhanced healing
time by 35-50 percent. Currently, horseshoe crabs are harvested
on a limited basis to manufacture chitin-coated suture material
and chitin wound dressings (Hall, 1992). Horseshoe crab blood is
also beneficial in cancer research; the LAL could lead to
controlled cancer therapy. Endotoxins and other substances in
horseshoe crab blood may have the potential for diagnosing
leukemia.
1.3.3. Recreational Fishery
There are no known recreational fisheries for the horseshoe crab.
1.4. ECOLOGICAL IMPORTANCE OF HORSESHOE CRABS
Horseshoe crabs play an important ecological role in the food web
for migrating shorebirds, finfish, and Atlantic loggerhead
turtles, a federally listed (threatened) species that uses the
Chesapeake Bay as a summer nursery area (Keinath et al. 1987).
1.4.1. Shorebirds
The Delaware Estuary is the largest staging area for shorebirds
in the Atlantic Flyway and is the second largest staging site in
North America (New Jersey Division of Fish, Game and Wildlife,
1994). An estimated 425,000 to 1,000,000 migratory shorebirds
converge on the Delaware Bay to feed and rebuild energy reserves
prior to flying an additional 4,000 kilometers to complete their
northward migration (Wander and Dunne, 1982; Dunne et al., 1982;
Clark et al., 1993). Migratory shorebirds arrive in Delaware Bay
and adjacent areas along the Atlantic coast at the peak of
horseshoe crab mating in mid-May through early-June, typically
spending two weeks in the area. Clark (1996) states that the
number of shorebirds coming to the Delaware Bay on spring
migrations is between 900,000 and 1.5 million of six species. At
least 11 species of migratory birds use horseshoe crab eggs to
replenish their fat supply during their trip from South American
wintering areas to Arctic breeding grounds (Myers, 1986). The
principle shorebirds observed include ruddy turnstone (Arenaria
interpres), red knot (Calidris canutus), semipalmated sandpiper
(Calidris pusilla), sanderling (Calidris alba), dowitcher
(Limnodromus spp.), and dunlin (Calidris alpina) (Dunne et al.,
1982). Other shorebirds frequenting sandy beaches include
western sandpiper (Calidris mauri), the federally listed
(threatened) piping plover (Charadrius melodus), black-bellied
plover (Pluvialis squatarola), semipalmated plover (Charadrius
semipalmatus), and willet (Catoptrophorus semipalmatus) (Burger,
et al., 1977). The dominant species of shorebirds that use the
Delaware Bay for staging are the red knot, ruddy turnstone,
semipalmated sandpiper, and sanderling, representing
approximately 88 percent of all shorebirds within the Delaware
Bay (Gelvin-Innvaer, 1996). The Delaware Bay staging area is
unique and of particular importance to shorebirds for the
following reasons: shorebirds use few major stopovers during the
spring migration; shorebirds arrive at stopover sites with little
or no fat reserves; and, shorebirds demonstrate fidelity to
staging areas (Wander and Dunne, 1982). An estimated 80 percent
and 30 percent of the hemispheric population of red knots and
sanderlings, respectively, use the Delaware Bay as a staging area
(American Bird Conservancy, 1997).
Despite high shorebird abundance within the Delaware Bay, counts
of sanderlings and semipalmated sandpipers declined significantly
over a 7-year period from 1985 to 1992 (Clark et al., 1993). The
decline in shorebirds in the Delaware Bay between 1986 and 1997
is statistically significant (p<0.05) (Clark and Niles,
unpublished data, 1997). The Delaware Division of Fish and
Wildlife also reports a 45 percent decline in peak counts of
shorebirds from 1990-1996 compared to data from 1986-1989. The
International Shorebird Survey also indicated a decline in
sanderlings between 1975 and 1983. Declines in shorebird numbers
may be the result of several threats, including the potential
overharvest of horseshoe crabs.
During the 2-3 week staging period, shorebirds undergo weight
gains of 40 percent or more (e.g., increasing body weight from 54
to 79 grams over 3 weeks) (Myers, 1986). Much of this weight
gain results from feeding on horseshoe crab eggs. In particular,
sanderlings are estimated to consume as much as 30.9 grams of
eggs per day per bird (approximately 8,300 eggs / day / bird).
However, the estimated overall metabolic efficiency is low (i.e.,
39 percent) and is among the lowest recorded value of a
vertebrate feeding on food of animal origin, based on experiments
on captive birds (Castro et al., 1989). Low metabolic efficiency
is attributable to the high percentage of eggs that pass through
the bird's digestive tract unbroken. Metabolic efficiency of
broken horseshoe crabs eggs is much higher (e.g., 69 percent)
than the metabolic efficiency of unbroken horseshoe crab eggs
(Castro et al., 1989). Tsipoura and Burger (1998) indicate that
under natural conditions, assimilation efficiency of horseshoe
crab eggs may be higher than suggested by Castro et al. (1989)
because sand in the diet may assist in breaking and grinding down
horseshoe crab eggs.
Shorebirds require high daily energy inputs due to their high
basal metabolic rates. In addition, shorebirds typically have
high daily energy expenditures, and are among the longest-
distance migrant animals in the world (Kersten and Piersma, 1987;
Myers et al., 1985). Castro et al. (1989) concluded that
sanderlings (and possibly other shorebirds) compensate for low
metabolizable energy of horseshoe crab eggs by consuming large
quantities of eggs. This is possibly due to the sheer abundance
of eggs, the ease in obtaining them, and the rapidity in which
they pass through the digestive tract.
Rather than probing below the surface of the substrate,
shorebirds typically forage for horseshoe crab eggs as the eggs
are uncovered by successive waves of nesting crabs and erosion
from localized storms (Botton et al., 1994). Horseshoe crab eggs
are the most abundant food item on Delaware Bay beaches during
the migratory staging of shorebirds. Botton et al. (1994) found
few other available macroinvertebrates and concluded that
shorebirds are feeding primarily on horseshoe crab eggs, largely
because of their abundance. However, it is likely that
shorebirds supplement their diet with ingestion of other food
items during the stopover period (Botton, 1984b).
Macroinvertebrate densities on the Delaware Bay beaches rarely
exceeded 200/m2 during horseshoe crab spawning season and are
several orders of magnitude less than horseshoe crab egg
densities. As a result, shorebirds showed a preference for
beaches with higher number of horseshoe crab eggs (Botton et al.,
1994). Access to horseshoe crab eggs by shorebirds may be
limited by tidal cycle, human disturbance, and competition among
shorebirds and gulls. Burger et al. (1996) concluded that a
mosaic of habitat types ranging from mudflats to high marshes is
essential to sustain the high population of shorebirds using
Delaware Bay during spring migration. In addition, Burger et al.
(1996) documented the importance of marshes for foraging in
several species of shorebirds. Shorebirds do abandon beaches at
night to roost in isolated marshes. This is believed to be
related to reducing risk of predation by nocturnal wildlife
(Bryant and Pennock, 1991). Clark et al. (1993) estimated that
only 15-20 percent of semipalmated sandpipers and up to 30
percent of dunlins were observed in salt marshes (feeding on prey
other than horseshoe crab eggs), as opposed to beaches.
Forage data (stomach contents) collected from sanderlings, ruddy
turnstones, least sandpipers, semipalmated sandpipers, dunlins,
and red knots on Delaware Bay beaches along the New Jersey coast
(N=70) indicate that horseshoe crab eggs represent the majority
of food items taken by shorebirds (15 to 95 percent) in 1996 and
1997, averaging 57.3 percent (Tsipoura and Burger, 1998). As
such, horseshoe crab eggs were not taken to the exclusion of
other items, such as polychaete worms and arthropods. Based on
fat-free weights, red knot, ruddy turnstone, sanderling, and
semipalmated sandpiper increased body mass up to 70 to 80 percent
while staging on Delaware Bay (Tsipoura and Burger, 1998). This
rate of weight gain is the highest recorded for any stopover site
in the world and is considered to be the result of feeding on
horseshoe crab eggs. Additionally, Tsipoura and Burger (1998)
reported that the mass movement of shorebirds (from the New
Jersey side to the Delaware side of the Delaware Bay) is
correlated with availability of horseshoe crab eggs. The ruddy
turnstone provides one possible exception to the interaction
between horseshoe crab egg availability and bird distribution.
These birds use their bill to dig into the sand and make holes
that are several inches deep, thereby reaching the eggs that are
buried deeper in the substrate. Tsipoura and Burger (1998) found
high concentrations of egg membranes in gut samples of ruddy
turnstones that were captured on Thompson's Beach, New Jersey and
hypothesized that the decline in abundance of surface eggs may
not have been a deterrent to the foraging success of this
species, as long as there were still sufficient numbers of eggs
available in the lower strata.
Despite significant shorebird predation on horseshoe crab eggs,
such activity probably has little impact on the horseshoe crab
population (Botton et al., 1994). Horseshoe crabs place egg
clusters at depths greater than 10 centimeters, which is deeper
than most short-billed shorebirds can reach. Horseshoe crab eggs
brought to the surface by wave action and burrowing activity by
spawning horseshoe crabs that are available for shorebird
predation would probably not survive to hatching due to heat
stress or desiccation (Botton et al., 1994). Additionally,
horseshoe crabs continue to spawn at least one month after the
departure of most of the shorebirds. Horseshoe crab larval
densities have been observed regularly exceeding 100,000/m2 in
July and August (Botton et al., 1992). For these reasons, it is
unlikely that shorebird predation has a substantial adverse
impact on the reproductive success of horseshoe crabs in Delaware
Bay.
The food supply provided by horseshoe crab eggs in Delaware has
been estimated at 320 tons (Delaware Department of Natural
Resources and Environmental Control, 1987). Castro and Myers
(1993) estimated the total energy requirement of shorebirds and
calculated that 539 metric tons of horseshoe crab eggs would be
needed to sustain the spring migration of shorebirds through the
Delaware Bay (assuming the shorebirds ate only horseshoe crab
eggs). Based on this estimate, Castro and Myers (1993) estimated
that the total number of females needed to lay the eggs consumed
by shorebirds is approximately 1,820,000. Assuming a sex ratio
of 1:1, approximately 3,640,000 horseshoe crabs are required to
sustain the shorebird migration stopover in Delaware Bay.
However, these calculations assume that shorebirds feed
exclusively on horseshoe crab eggs. Tsipoura and Burger (1998)
indicated that horseshoe crab eggs are a significant part of
shorebirds diet, but that diet is supplemented by other food
resources. Botton et al. (1994) estimated that an average of
44,000 eggs/m2 would be needed to sustain the entire shorebird
population in the Delaware Bay. Their data indicate these
densities currently occur within most Delaware Bay beaches. A
significant decrease in the number of horseshoe crabs could leave
a large portion of migrating shorebirds without either the
necessary food resources to complete their trip to the Arctic
breeding grounds or the necessary fat reserves upon arrival to
initiate egg laying and incubation.
1.4.2. Finfish
Horseshoe crab eggs and larvae are a seasonal food item of
invertebrates and finfish. In the Delaware River from May
through August, striped bass (Morone saxatilis) and white perch
(Morone americana) eat horseshoe crab eggs. American eel
(Anguilla rostrata), killifish (Fundulus spp.), silver perch
(Bairdiella chrysoura), weakfish (Cynoscion regalis), kingfish
(Menticirrhus saxatilis), silversides (Menidia menidia), summer
flounder (Paralichthys dentatus), and winter flounder
(Pleuronectes americanus) also eat eggs and larvae (Shuster,
1982). All crab species and several gastropods, including
whelks, feed on horseshoe crab eggs and larvae. Shuster (1982)
reported a large leopard shark (Triakis semifasciatum) preying on
adult horseshoe crabs in southern Florida.
1.4.3. Sea Turtles
Lutcavage and Musick (1985) examined the stomach contents or
excreta from 527 loggerhead turtles from Chesapeake Bay and
nearby coastal waters and found that the most common prey was
horseshoe crab. Musick et al. (1983) examined 27 loggerhead
turtles and found horseshoe crabs commonly in stomach contents.
Similarly, Lutcavage (1981) found that horseshoe crabs
represented up to 42 percent of the diet of loggerhead turtles
from Chesapeake Bay (N=6), averaging 22 percent. Data collected
by the NMFS Sea Turtle Stranding and Salvage Network along the
Atlantic Coast identified horseshoe crabs in 75 percent of
loggerhead stomach contents in 1996 (N=8) and 55 percent in 1997
(N=11) (Evans, pers. comm., 1998). Morreale and Standora (1993)
found no evidence of horseshoe crabs in loggerhead turtle diets
in New York's Long Island Sound; however, diet largely depends on
the relative abundance of prey species. Maintaining abundant
stocks of adult horseshoe crabs may be an important component of
ensuring the long-term survival of loggerhead sea turtles in the
Chesapeake Bay area.
1.5. HABITAT CONSIDERATIONS
1.5.1. Description of Habitat
Essential habitat is defined as those waters and substrate
necessary for fish spawning, breeding, feeding, or growth to
maturity. Horseshoe crabs use a different habitat at different
life stages. Protected beaches provide essential habitat for
horseshoe crab spawning efforts, while nearshore shallow waters
are essential for nursery habitat.
1.5.1.1. Spawning Habitat
Spawning adults prefer sandy beach areas within bays and coves
that are protected from wave energy. Beach habitat also must
include porous, well-oxygenated sediments to provide a suitable
environment for egg survival and development (Botton, et al.,
1988). Optimal spawning areas are limited by the availability of
suitable sandy beach habitat. However, spawning may occur along
peat banks if there is sand in the upper intertidal regions and
along the mouths of salt marsh creeks (Botton, 1995). Shuster
(1996) states that spawning may occur along muddy tidal stream
banks, but not on peat banks because adults are sensitive to
hydrogen sulfide and anaerobic conditions. Spawning habitat
varies throughout the horseshoe crab range. In Massachusetts,
New Jersey, and Delaware, beaches are typically coarse-grained
and well-drained as opposed to Florida beaches, which are
typically fine-grained and poorly drained. These differences
affect nest-site selection and nesting synchrony (Penn and
Brockmann, 1994). Thompson (1998) found that preferentially
selected spawning sites were located adjacent to large intertidal
sand flat areas, which provide protection from wave energy and an
abundance of food for juveniles. A Habitat Suitability Index
model was developed for horseshoe crab spawning habitat within
the Delaware Bay; however, this model is currently in draft form
and has not completed peer review, testing, or publication by the
U.S. Fish and Wildlife Service (Brady and Schrading, 1996).
1.5.1.2. Nursery Habitat
The shoalwater and shallow water areas of bays (e.g., Delaware
Bay and Chesapeake Bay) are essential nursery areas (Botton,
1995). Juveniles usually spend their first two years on
intertidal sand flats (Rudloe, 1981). Thompson (1998) also found
significant use of sand flats by juvenile horseshoe crabs in
South Carolina. However, older juveniles and adults are
exclusively subtidal, except during spawning.
1.5.1.3. Adult Habitat
Specific requirements for adult habitat are not known. Although
horseshoe crabs have been taken at depths >200 meters, Botton and
Ropes (1987a) suggest that adults prefer depths <30 meters. The
NMFS Northeast Fishery Center bottom trawl surveys collected 92
percent of their horseshoe crabs at these depths, even though 73
percent of the sampling effort was expended in depths >27 meters.
During spawning season adults typically inhabit bay areas
adjacent to spawning beaches and feed on bivalves. In the fall,
adults may remain in bay areas or migrate into the Atlantic Ocean
to overwinter on the continental shelf.
1.5.2. Identification and Distribution of Essential Habitat
Beach areas that provide spawning habitat are considered
essential habitats for adult horseshoe crabs. Nearshore, shallow
water, intertidal flats are considered essential habitats for the
juvenile development. Delaware Division of Fish and Wildlife's
16-foot bottom trawl survey data indicated that over 99 percent
of juvenile horseshoe crabs (<160 mm prosomal width) were taken
at salinities >5 parts per thousand (Michels, 1997). Larger
juveniles and adults use deep water habitats to forage for food,
but these are not considered essential habitat. Of these
habitats, the beaches are the most critical (Shuster, 1994).
Optimal spawning beaches may be a limiting reproductive factor
for the horseshoe crab population. Based on geomorphology
Botton, et al. (1992) estimated that only 10 percent of the New
Jersey shore adjacent to Delaware Bay provided optimal horseshoe
crab spawning habitat. The densest concentrations of horseshoe
crabs in New Jersey occur on small sandy beaches surrounded by
salt marshes or bulkheaded areas (Loveland et al., 1996).
Prime spawning habitat is widely distributed throughout
Maryland's Chesapeake and coastal bays, including tributaries.
Horseshoe crabs are restricted to areas that exceed 7 parts per
thousand salinity (Maryland Department of Natural Resources,
1998). In the Chesapeake Bay, spawning habitat generally extends
to the mouth of the Chester River, but can occur farther north
during years of above normal salinity levels. Prime spawning
beaches within the Delaware Bay consist of sand beaches between
Maurice River and the Cape May Canal in New Jersey and between
Bowers Beach and Lewes in Delaware (Shuster, 1994).
1.5.3. Present Condition of Habitats and Essential Habitats
1.5.3.1. Quantity
The United States has approximately 100,400 acres of marine
intertidal shoreline, based on 1980s estimates (Frayer, 1991).
However, this estimate includes marine intertidal habitat on the
Pacific Coast and does not necessarily represent potential
horseshoe crab spawning habitat. Within the southeastern United
States (from North Carolina to Florida), there were 49,100 acres
of marine intertidal habitat based on an estimate in the 1980s
(Hefner, et al., 1994). These values represent maximum potential
spawning habitat for horseshoe crabs. Actual spawning habitat
used by horseshoe crabs is considerably less because horseshoe
crabs typically select beaches based on geochemical criteria.
For example, Botton, et al. (1988) conducted beach surveys on
approximately 80 kilometers of beach along the New Jersey side of
the Delaware Bay. Only 10.6 percent (8.5 kilometers) provided
optimal spawning habitat and only 21.1 percent (17.0 kilometers)
provided suitable spawning habitat.
1.5.3.2. Quality
As discussed in section 1.5.3.1., studies conducted by Botton, et
al. (1988), showed that only 31.7 percent of marine intertidal
habitat surveyed provided optimal or suitable spawning habitat
for horseshoe crabs. Viable spawning habitat throughout the
Atlantic coast is probably only a fraction of total marine
intertidal areas.
1.5.3.3. Loss and Degradation
Habitat degradation is likely an important component of the
population dynamics of horseshoe crabs. Groins and bulkheads may
adversely impact horseshoe crab spawning habitat. Bulkheads may
block access to intertidal spawning beaches, while groins and
seawalls intensify local shoreline erosion and prevent natural
beach migration. An estimated 10 percent of the New Jersey
shoreline adjacent to the Delaware Bay has been severely
disturbed by shoreline protection structures (Botton, et al.,
1988). Rip-rap and revetments also adversely impact horseshoe
crabs by minimizing potential spawning sites and by entrapping
and stranding them. A contributing factor in the decline of
horseshoe crabs in the Delaware Bay between 1871 and 1981 may be
the increased number of jetties and residential development
(Shuster and Botton, 1985).
Shoreline erosion combined with shoreline development results in
the loss of potentially suitable spawning beaches. Beach
migration is a coastwide phenomenon, where beaches move landward
associated with erosional events. However, hard structures
(e.g., bulkheads, seawalls, revetments) associated with beach
development interfere with the natural beach migration causing
habitat loss. Beaches along the New Jersey shore of the Delaware
Bay have generally eroded at varying rates ranging from 1 to 12
feet per year for the last 100 years (U.S. Army Corps of
Engineers, 1997). Erosion rates from 1 to 26 feet per year,
averaging approximately 3 to 5 feet per year and the existence of
hard structures limiting beach migration have resulted in a
decline in Delaware beaches (U.S. Army Corps of Engineers, 1991).
McCormick and McCormick (1998) report that the annual rate of
erosion in the Chesapeake Bay averages 1 foot per year.
Shoreline areas with high concentrations of silt or peat are less
favorable to horseshoe crabs because the anaerobic conditions
reduce egg survivability. Horseshoe crabs may detect hydrogen
sulfide (which is produced in the anaerobic conditions of peat
substrates) or low oxygen conditions, and actively avoid such
areas (Botton et al., 1988). Erosion affects spawning by
influencing beach characteristics that are most important in site
selection, such as beach topography, sediment texture, and
geochemistry (Botton et al., 1988).
1.5.3.4. Current Threats
The rate at which coastal wetlands and beach areas are lost is
directly related to human population density (Gosselink and
Baumann, 1980). Impacts on beaches from development and related
infrastructure (e.g., bulkheads, groins, revetments, and
seawalls) continue to degrade essential horseshoe crab habitat.
By reducing the amount of wave action sustained by a particular
beach, jetties may benefit horseshoe crab spawning activities
(Maryland Department of Natural Resources, unpublished data,
1998). Erosion and shoreline protection structures (e.g.,
bulkheads, seawalls, revetments constructed to minimize erosion
impacts) compromise the integrity of essential habitat through
both the erosional process itself and interference with natural
beach migration. Channel dredging and overboard spoil disposal
are common throughout the Atlantic coast, but effects on
horseshoe crabs are currently unknown.
Horseshoe crabs are relatively tolerant of petroleum
hydrocarbons, but the tolerance decreases with increasing
temperature. Exposure to oil and chlorinated hydrocarbons
resulted in delayed molting and elevated oxygen consumption in
horseshoe crab eggs and juveniles (Laughlin and Neff, 1977).
Maghini (1996) found trace metal and organochlorine
concentrations to be relatively low in shorebird, horseshoe crab,
and substrate samples from Delaware beaches and concluded that
existing concentrations were of low toxicological concern. In
the Delaware Bay, Burger (1997) identified low levels of mercury
(27 to 93 ppb) in horseshoe crab eggs between 1993 and 1995 and
low cadmium levels in 1993 and 1995 (17 ppb and 24 ppb,
respectively), but relatively higher levels in 1994 (310 ppb).
Lead (558 to 87 ppb), chromium (5,059 to 250 ppb), and manganese
(18,371 to 7,118 ppb) levels in eggs generally decreased from
1993 to 1995 in the Delaware Bay, while selenium levels (1,965 to
3,472 ppb) increased in those years (Burger, 1997). Burger
(1997) concluded that the additional stress from heavy metals on
horseshoe crab eggs could impair reproduction.
Based upon studies of other invertebrates, insecticides used for
mosquito control may adversely impact juvenile horseshoe crabs
(Breese, pers. comm., 1998). Additionally, red tide events may
result in significant mortality, particularly to juveniles
inhabiting intertidal areas and tidal flats (Rudloe, pers. comm.,
1998).
Because the Delaware estuary is a major petrochemical center on
the East Coast (Sharp, 1988), oil spills during the horseshoe
crab spawning season could threaten populations in the Delaware
Bay. In addition, mercury, lead, zinc, and cadmium may be of
concern in some coastal estuaries and rivers, such as the
Cohansey (New Jersey) and Saint Jones (Delaware) Rivers (Sharp,
1988). Delaware Division of Fish and Wildlife's 16-foot trawl
survey data indicate the area off the Saint Jones River is a
major nursery area for horseshoe crabs.
1.6. IMPACTS OF THE FISHERY MANAGEMENT PROGRAM
1.6.1. Biological and Environmental Impacts
The SAC concluded that the horseshoe crab population in the mid-
Atlantic region has remained stable in recent years (Atlantic
States Marine Fisheries Commission, 1998). However, evidence
based on the Delaware trawl survey and egg count data suggest
that the Delaware Bay population may have declined due to harvest
activities. Several factors contribute to the risk that
harvesting may adversely effect horseshoe crab populations: (1)
horseshoe crabs mature slowly, requiring 9 to 11 years to attain
sexual maturity (Shuster and Botton, 1985); (2) some bait
harvesters prefer gravid females; (3) horseshoe crabs aggregate
inshore seasonally to spawn; and, (4) changes in abundance
(increases or decreases) are not readily recognizable because
they occur over a period of years (Shuster, 1996). Population
data indicate that after harvesting ceases, horseshoe crabs do
not rebound for approximately one decade, corresponding to the
time required for horseshoe crabs to reach sexual maturity
(Shuster, 1994).
The commercial fishery competes with fish and wildlife resource
needs, particularly shorebirds and sea turtles. Identifying and
maintaining optimal sustainable yield may not be adequate to meet
the needs of both fish and wildlife resources and the commercial
fishery. Shorebirds primarily feed on horseshoe crab eggs
exposed on the surface, which do not contribute to the horseshoe
crab population (Botton et al., 1994). Sufficient surface eggs
are available only if horseshoe crabs are spawning at high
densities. Therefore, adequate spawning densities must be
maintained to ensure availability of horseshoe crab eggs for
shorebirds. Sea turtles feed on adult horseshoe crabs, but their
diet depends on relative abundance of the prey species.
Appropriate coastwide management of the horseshoe crab population
would ensure the long-term viability of the population for
continued harvest and would provide necessary quantities of
adults and eggs for fish and wildlife resources.
1.6.2. Socioeconomic Impacts
Horseshoe crabs are the primary bait for the American eel and
conch fisheries in many mid-Atlantic States. In Maryland, the
estimated value of the horseshoe crab fishery in 1996 for 10
horseshoe crab harvesters was $398,596 (Maryland Department of
Natural Resources, 1998). Also in 1996, one Maryland seafood
dealer who supplies horseshoe crabs to 20 American eel and 25
conch harvesters, estimated that the value of horseshoe crabs for
these fisheries was $151,200. Horseshoe crab prices vary and are
reported to be between $0.65 to $0.75 per horseshoe crab
(Maryland Department of Natural Resources, 1998).
In 1997, American eel and conch harvesters in Delaware used an
average of 4,714 and 20,502 horseshoe crabs per season per
harvester, respectively; while in New Jersey, American eel and
conch harvesters used an average of 4,005 and 22,654 horseshoe
crabs per season per harvester, respectively (Munson, 1998).
Many conch and American eel harvesters in New Jersey and Delaware
harvest their own bait, supplying 18 to 65 percent of their bait
needs (Munson, 1998). While only 9 percent of the fishing income
(of respondents in the Delaware Bay Watermen's study) is
attributable to the direct sale of horseshoe crabs, an average of
58 percent of the eel and conch fishing income depends on using
horseshoe crabs as bait (Munson, 1998). American eel harvesters
in Delaware Bay report about 21 percent of their total fishing
income is attributable to eeling, while conch harvesters report
an average of 53 percent of their total fishing income depends on
the conch fishery (Munson, 1998). In 1996, the commercial
harvest of horseshoe crabs was estimated to be a $1.5 million
industry.
Horseshoe crabs are vital to medical research and the
pharmaceutical products industry. The worldwide market for LAL
is currently estimated to be approximately $50 million per year.
This estimate is based on bleeding 250,000 horseshoe crabs per
year, generating approximately $200 per crab in revenue for the
biomedical industry. The biomedical industry either directly
collects horseshoe crabs on spawning beaches or purchases
horseshoe crabs at prices up to $3.00 per crab. The biomedical
industry pays approximately $375,000 per year for horseshoe crabs
based on using an estimated 250,000 horseshoe crabs at an average
price of $1.50 per crab.
Eco-tourism is critical to many states economies (e.g., New
Jersey and Delaware) and depends on the abundance and health of
ecosystems within the region. In 1988, over 90,000 "birders"
spent $5.5 million in Cape May, New Jersey (Kerlinger and
Weidner, 1991) to watch the interaction between spawning
horseshoe crabs and migrating shorebirds. In 1996, approximately
606,000 people in New Jersey and Delaware took trips away from
their residence (> 1 mile) for the primary purpose of wildlife
watching (e.g., observing, photographing). Of these people,
409,000 people identified watching shorebirds from a list of
birds that included raptors, waterfowl, and songbirds (U.S.
Bureau of Census and U.S. Fish and Wildlife Service, 1998). In
1996, New Jersey and Delaware wildlife watchers spent between 9
and 12 days per year (on average) away from home (> 1 mile)
watching wildlife (U.S. Bureau of Census and U.S. Fish and
Wildlife Service, 1998). Total expenditures (including food,
lodging, transportation, and equipment) in 1996 for the primary
purpose of wildlife watching in New Jersey and Delaware was
$639,992,000 (U.S. Fish and Wildlife Service, 1998). However,
the type of wildlife watched was not identified. The 1996
regional economic impact resulting from expenditures by wildlife
watchers in New Jersey and Delaware is the creation of 15,127
jobs and the generation of a total household-income of $399
million (U.S. Fish and Wildlife Service, 1998).
2.0. GOALS AND OBJECTIVES
The goal of this Plan is to conserve and protect the horseshoe
crab resource to ensure its continued role in the ecology of the
coastal ecosystem, while providing for continued use over time.
Specifically, the goal includes management of horseshoe crab
populations for continued use by:
o current and future generations of the fishing and non-
fishing public (including the biomedical industry,
scientific and educational research);
o migrating shorebirds; and,
o other dependent fish and wildlife, including federally
listed (threatened) sea turtles.
To achieve this goal, the following objectives must be met:
(a) prevent overfishing;
(b) achieve compatible and equitable management measures
among jurisdictions throughout the fishery management
unit;
(c) promote cooperative interstate research, monitoring,
and law enforcement;
(d) identify critical habitats and environmental factors
that limit long-term productivity of horseshoe crabs;
(e) adopt and promote standards of environmental quality
necessary for the long-term maintenance and
productivity of horseshoe crabs throughout their range;
and,
(f) establish standards and procedures for implementing the
Plan and criteria for determining compliance with Plan
provisions.
The fishery management unit includes all horseshoe crab stocks of
the Atlantic Coast of the United States. To facilitate
implementation, the management unit may be subdivided into New
England estuaries and shoreline (Maine through Connecticut), Long
Island Sound and New York Bight, Delaware Bay, and Chesapeake Bay
including the Delmarva Coast (New York to Virginia), and the
South Atlantic Bight (North Carolina to Florida). These
subdivisions are based on harvest pressure, recognizably separate
populations, and abundance of horseshoe crabs.
3.0. MANAGEMENT PROGRAM SPECIFICATIONS / ELEMENTS
Management of the species will be based on scientific advice
provided by state and federal biologists, as well as input from
public hearings and an ASMFC Citizen's Advisory Panel.
Management will strive for long-term viable populations
supporting sustainable fisheries (including the biomedical
industry) and dependent fish and wildlife resources. Effective
management may require monitoring coupled with controls on
fishing mortality and habitat degradation. The measures outlined
below are designed to facilitate the management process. As new
data become available and new assessments are completed,
management activities will be adjusted accordingly.
3.1. ECOLOGICAL CONSIDERATIONS
Horseshoe crabs are an important component of the ecosystem. A
certain amount of egg and adult biomass must be maintained to
meet the needs of those species for which the horseshoe crab is
an important food source.
Shorebirds rely on horseshoe crab eggs to replenish their fat
reserves to continue their spring migration. Based on total
energy requirements of sanderlings, Castro and Myers (1993)
projected that 539 metric tons of horseshoe crab eggs would be
needed to sustain the spring migration of shorebirds through the
Delaware Bay (assuming the shorebirds ate only horseshoe crab
eggs). To meet this need, Castro and Myers (1993) estimated that
approximately 3,640,000 horseshoe crabs (assuming a sex ratio of
1:1) are required to meet this need. Recent work by Tsipoura and
Burger (1998) shows that shorebird diet during spring stopovers
does not consist entirely of horseshoe crab eggs. While the 539
metric tons may be an overestimate of the need, the importance of
horseshoe crab eggs to the diet of shorebirds is not diminished.
Horseshoe crab eggs and larvae are a seasonal food item of
various finfish, such as striped bass and white perch, as well as
all crab species and several gastropods (Shuster, 1982). The
degree of dependence upon horseshoe crab eggs and larvae by these
species is unknown.
Horseshoe crabs are dietary components of the federally listed
(threatened) loggerhead turtle. The extent to which loggerhead
turtles rely on horseshoe crabs is unknown, but data collected in
the mid-Atlantic coast region by NMFS and other researchers
showed that a majority of loggerhead turtle stomachs examined
contained horseshoe crabs. Federally listed species are afforded
protection under the Endangered Species Act (87 Stat. 884, as
amended; 16 U.S.C. 1531 et seq.) pursuant to Section 7(a)(2),
which requires every federal agency to ensure that any action it
authorizes, funds, or carries out is not likely to jeopardize the
continued existence of any listed species or result in the
destruction or adverse modification of critical habitat.
Jurisdiction for loggerhead turtle population management resides
with the NMFS (marine environment) or the U.S. Fish and Wildlife
Service (USFWS) (onshore environment); therefore, the ASMFC
should initiate consultations regarding potential impacts of this
Plan on loggerhead turtles.
3.2. ASSESSING ANNUAL RECRUITMENT
Little is known about annual recruitment in horseshoe crabs.
Known factors include the following: maximum fecundity can be
estimated (Shuster, 1982); most eggs that remain buried, and are
not subject to shorebird predation, survive to hatching (Rudloe,
1979); and larval mortality from predation is substantial
(Loveland et al., 1996). However, the number of larvae that
survive to sexual maturity remains unknown. Because horseshoe
crabs are slow maturing, long-lived, and repetitive spawners,
current juvenile indexing techniques may have limited
applicability. Additional information regarding larval and
juvenile survival and mortality is essential to assessing annual
recruitment. In addition, the total number of adult, sexually
mature horseshoe crabs along the Atlantic Coast must be known to
estimate annual recruitment.
3.3. ASSESSING SPAWNING STOCK BIOMASS
The spawning stock biomass for horseshoe crab populations along
the Atlantic Coast is unknown. Botton and Ropes (1987a) provided
a conservative adult horseshoe crab estimate of 2.3 to 4.5
million for the Atlantic Coast between New Jersey and Virginia,
based on the NMFS Northeast Fisheries Center trawl survey data..
This region of the Atlantic Coast makes up the majority of the
horseshoe crab population within the Atlantic Coast (Botton and
Ropes, 1987a). However, this estimate of inshore abundance is
conservative, due to the inability of large trawling survey
vessels to operate in shallow water and because the gear type
used may not adequately sample horseshoe crabs.
The ASMFC SAC analyzed state and federal survey data and
determined that the horseshoe crab population in the mid-Atlantic
region has been stable in recent years (Atlantic States Marine
Fisheries Commission, 1998). However, some data, including the
Delaware trawl survey and egg count data collected by Dr. Robert
Loveland and Dr. Mark Botton, suggest a possible decline in
horseshoe crabs in the Delaware Bay in the 1990s. Additional
information on the stock assessment review completed by the ASMFC
SAC can be found in the ASMFC SAC report (Atlantic States Marine
Fisheries Commission, 1998).
3.4. ASSESSING MORTALITY
Horseshoe crab mortality has three components: natural mortality,
mortality associated with commercial biomedical applications, and
bait fishing mortality. Natural mortality includes beach
strandings, predation, and other factors such as disease and
accidents. Beach strandings may account for 10 percent of the
adult horseshoe crab population in Delaware Bay (Botton and
Loveland, 1989). Stranding mortality may be higher than the
reported 10 percent in areas where rip-rap and revetments entrap
horseshoe crabs. In other areas, strandings may account for a
much lower percentage (Rudloe, pers. comm., 1998). Shorebird
predation on eggs may simply remove excess production (i.e.,
surface eggs). Adult horseshoe crabs provide a component of
loggerhead turtle diets as evidenced by stomach content analyses.
The percent natural mortality attributable to other factors is
unknown.
Of the estimated 200,000 to 250,000 crabs bled by the biomedical
industry each year, perhaps as many as 10 to 15 percent of the
crabs do not survive the bleeding procedure, which comprises a
source of mortality not included in the commercial landing
statistics (Rudloe, 1983; Thompson, 1998). Mortality due to the
bleeding procedure may be lower (e.g., 0 to 4 percent), depending
on the individual biomedical facility (Swan, pers. comm., 1998).
However, the mortality associated with collecting, shipping, and
handling remains unknown. Currently, the biomedical industry is
estimated to account for the mortality of 20,000 to 37,500
horseshoe crabs per year (10 to 15 percent).
Fishing mortality is the rate at which fish are removed from the
population by human activities and may include directed fishing
mortality (e.g., intentional legal harvest) and nonharvest
mortality (e.g., poaching and by-catch). The 1996 fishing
mortality accounted for approximately 2 million individuals
throughout the Atlantic Coast, with approximately 1.7 million
individuals being taken between New Jersey and Virginia based on
landings data provided by individual states and the National
Marine Fisheries Service (1998). Reported commercial landings
data show a substantial increase in harvest during the 1990s,
which may be a function of an increase in fishing effort and an
increase in reporting. The SAC concluded that the reported
landings seem not to have had an adverse impact on the horseshoe
crab population, based on available trawl survey data (Atlantic
States Marine Fisheries Commission, 1998). However, due to
inadequacies in the survey design of many of the population
surveys and the potential decreases identified by the Delaware
trawl survey and egg count data, the Horseshoe Crab Technical
Committee recommended an independent review of the SAC report and
additional evaluation of egg count data.
3.5. SUMMARY OF MONITORING PROGRAMS
Numerous state and federal agencies, universities, and private
organizations are involved in data-collection efforts to
ascertain horseshoe crab population status. Monitoring and
evaluation efforts specific for horseshoe crabs include egg
counts in Delaware Bay (New Jersey and Delaware) by Dr. Robert
Loveland of Rutgers University and Dr. Mark Botton of Fordham
University, egg counts by Dr. Richard Weber of the University of
Delaware, spawning surveys in Delaware Bay (New Jersey and
Delaware) by Limuli Laboratories, and spawning surveys in
Maryland's Chesapeake and coastal bays by Maryland Department of
Natural Resources. Trawl surveys are conducted along the New
Jersey Atlantic Coast by New Jersey Division of Fish, Game and
Wildlife and within the Delaware Bay by the Delaware Division of
Fish and Wildlife. Trawl surveys have been conducted along
Maryland's Atlantic Coast bays by Maryland Department of Natural
Resources, and in Peconic Bay, New York by New York State
Department of Environmental Conservation. The NMFS Northeast
Fishery Center, the State of Massachusetts, and the Connecticut
Department of Environmental Protection also conduct trawl
surveys. South Carolina Department of Natural Resource's
Crustacean Management Section conducts trawl surveys in five
estuaries in South Carolina. The National Oceanic and
Atmospheric Administration / SEAMAP conducts shallow water trawl
surveys between South Carolina and Florida. Limuli Laboratories
and Maryland Department of Natural Resources also conduct tagging
studies. Concurrently, several shorebird monitoring efforts are
being conducted, including aerial surveys, diet / weight-gain
studies, and banding studies by state and educational research
institutions.
While each of the above-mentioned monitoring programs are useful
in identifying general trends within specific areas, each is
complicated by factors that may bias the data, such as sampling
error, inappropriate equipment, or incomplete sampling effort.
The independent monitoring programs also lack a comprehensive
data collection goal. The goal of a comprehensive horseshoe crab
monitoring program should be to produce data necessary to develop
a stock assessment for the Atlantic Coast horseshoe crab
populations that can be used in future management decisions.
To collect information to assist in future management decisions,
a comprehensive monitoring plan must be developed throughout the
Atlantic Coast. Such monitoring efforts should be standardized
and occur in each of the cooperating states within the ASMFC.
Monitoring efforts must recognize the need to compare existing
survey information with future survey information, but not at the
expense of adequate design. Recommendations for such a
monitoring program include the following components:
Component A. Continue or initiate mandatory monthly reporting
of all harvest (including, but not limited to bait
fisheries, by-catch, biomedical industry, and
scientific and educational research harvest).
Reporting requirements should consist of numbers landed
and pounds landed by sex and harvest method. Each
state must characterize a portion of the commercial
catch based on prosomal width by sex. The approximate
location of horseshoe crab harvests is required to
determine where fishing effort is concentrated. If
horseshoe crabs are captured for biomedical use, all
states also must monitor and report monthly and annual
harvest of horseshoe crabs by biomedical facilities
(i.e., numbers), identify percent of mortality up to
the point of release (including harvest, shipping,
handling, and bleeding mortality), and certify that
harvested horseshoe crabs are being used by biomedical
facilities and not for other purposes. The use and
harvest of horseshoe crabs for scientific and
educational research should also be monitored and
reported by all states.
Component B. Continue existing benthic sampling programs in the
following states: Rhode Island, Massachusetts,
Connecticut, New York, New Jersey, Delaware, Maryland,
North Carolina, South Carolina, and Georgia. Benthic
sampling programs should record weight, number, and
prosomal width by sex of individuals collected. States
that currently collect data from juvenile trawl surveys
should include these data in annual monitoring reports.
Juvenile sampling programs should record number and
prosomal width (other data are not required).
Component C. Formulate standardized and statistically robust
methodologies (e.g., method of collection, survey time,
location, method of counting), survey cost, and
schedule for implementation for horseshoe crab egg
counts to identify trends in the annual spawning
horseshoe crab population and eggs available to
shorebirds by December 31, 1998. Implement
standardized methodology in New Jersey and Delaware by
the 1999 horseshoe crab spawning season.
Component D. Formulate standardized and statistically robust
methodologies (e.g., stratified random sampling design
described in Maio et al. (1998) or comparable
statistically robust methodology), survey cost, and
schedule for implementation for horseshoe crab spawning
surveys by December 31, 1998. Implement standardized
methodology in New Jersey, Delaware, and Maryland by
the 1999 horseshoe crab spawning season.
Component E. Evaluate the post-release mortality of horseshoe
crabs used by the biomedical industry by initiating a
tagging program. A coordinated tagging program shall
be developed by the Technical Committee (possibly
including release site location, numbers tagged, and
numbers recaptured) and implemented by the biomedical
industry. States that have biomedical industries would
be required to ensure that the subject biomedical
industries implement the tagging program and report
results of the tagging program to the states. States
shall include results of the tagging program in their
annual report.
Each state must implement at least components A, B, and E
identified above, to provide information on horseshoe crab
landings, post-release mortality, and trends from year to year.
The States of New Jersey and Delaware must implement Component C
and the States of New Jersey, Delaware, and Maryland must
implement Component D. The Horseshoe Crab Technical Committee
will provide guidance regarding the formulation of appropriate
methodologies (including appropriate equipment) for egg count
surveys, spawning surveys, and benthic sampling programs. Such a
comprehensive monitoring program must be initiated and continue
for several consecutive years to provide the most reliable data
on horseshoe crab population stocks. The monitoring program then
should be reevaluated and potentially conducted on a less
frequent basis. States that qualify for "de minimis status," are
exempt from all components of the monitoring program except
components A, B, and E.
3.6. BY-CATCH REDUCTION
The shrimp trawl fishery in the South Atlantic Bight may
contribute to horseshoe crab mortality via by-catch (Thompson,
1998). By-catch of horseshoe crabs has been greatly reduced with
the mandatory requirement to use turtle excluder devices in the
shrimp trawl fishery (Cupka, pers. comm., 1998). Dredging for
whelk in Virginia also may result in substantial by-catch of
horseshoe crabs. The amount of by-catch harvest remains unknown.
Additional information would be required to determine the
significance of by-catch. It is likely that by-catch horseshoe
crabs are sold for bait and may be reported in total harvest.
States and federal agencies must assess the magnitude of by-catch
mortality occurring in waters under their jurisdiction.
3.7. HABITAT IMPACTS
Potential loss of spawning habitat would result in significant
impacts on horseshoe crabs. Threats to horseshoe crab
populations and spawning habitat include sea level rise / land
subsidence, coastal erosion, channel dredging, and contaminants.
Global warming and the subsequent rise in sea level could
adversely affect horseshoe crab spawning activities. Sea level
is predicted to rise above current levels by approximately 50
centimeters to 1 meter by the year 2100 (Oerlemans 1989; Titus et
al., 1991). Land subsidence along the Atlantic Coast adds to the
effect of sea level rise, resulting in an increase of 25-30
centimeters greater than the global average (Hull and Titus,
1986).
Coastal erosion is a natural process and causes beaches to
retreat landward over time. Combined with shoreline development,
erosion adversely affects horseshoe crab spawning beaches.
Development adjacent to shorelines prevents the natural migration
of beaches landward. Construction of bulkheads, groins,
revetments, and seawalls protect shorelines by preventing natural
migration of beaches. Optimally, beaches should be permitted to
naturally migrate landward, but the presence of commercial and
residential development along the Atlantic Coast, makes this
infeasible in many areas. State and federal agencies charged
with shoreline protection are currently using beach nourishment
as the preferred shoreline protection strategy. Beach
nourishment protects development and infrastructure and may
provide habitat for horseshoe crab spawning. However, if beach
nourishment projects do not keep pace with erosion in developed
areas, potential horseshoe crab spawning beaches may be reduced.
Ultimately, the long-term and short-term benefits and potential
adverse impacts from beach nourishment projects on horseshoe
crabs must be assessed.
Channel dredging and overboard spoil disposal are common
throughout the Atlantic coast, but currently have unknown effects
on horseshoe crabs. Changes in salinity as a result of dredging
projects could alter horseshoe crab distribution. Additionally,
dredging associated with whelk and other fisheries may damage
horseshoe crab benthic habitat; however, the significance of this
impact also remains unknown.
Pollution has the potential to adversely impact the horseshoe
crab population or its habitat. Currently, there are no data to
suggest unusual sensitivity by horseshoe crabs to urban or
agricultural contaminants (e.g., pesticides and herbicides)
(Botton, 1995). However, mosquito control agencies in New Jersey
and Delaware have recently expanded their use of the mosquito
larvicide methoprene, an insect growth regulator (IGR) that
mimics juvenile growth hormones. Insecticides such as IGRs have
been found to adversely effect crustaceans when they attempt to
molt. Certain IGRs, Dimilin¨ (a chitin-inhibitor), can cause
death in horseshoe crabs at the larval stage (Kas'yanov and
Costlow, 1984). Additional information should be collected to
determine the impacts on horseshoe crabs from such larvicides.
Maghini (1996) found concentrations of trace metals and
organochlorines to be relatively low in shorebird, horseshoe
crab, and substrate samples from Delaware beaches and concluded
that existing concentrations were of low toxicological concern.
Oil is also a potential threat to horseshoe crab habitat and
populations. The impacts of an oil spill on spawning beaches
during the spawning season could be catastrophic for horseshoe
crabs and shorebirds.
4.0. MANAGEMENT PROGRAM IMPLEMENTATION
The ASMFC encourages all states to implement uniform standards
for managing the horseshoe crab along the Atlantic Coast. Each
state is responsible for implementing management measures and
protecting horseshoe crab habitat within its jurisdiction to
ensure the viability of the population segment, either produced
or residing within its boundaries.
4.1. RECREATIONAL FISHERIES MANAGEMENT MEASURES
Since there are no known recreational fisheries for the horseshoe
crab, no recreational fisheries management measures are proposed.
4.2. COMMERCIAL FISHERIES MANAGEMENT MEASURES
Commercial landings data show a substantial increase in reported
harvest during the 1990s, which may be a result of improved
reporting and / or increased fishing effort. Due to the
uncertainty of the stock assessment and reported harvest data,
the selection of conservative commercial fisheries management
measures may be prudent.
4.2.1. Management Measures for Bait Fisheries
Several management options described below are dependent on the
reference period landings (i.e., Table 3), which are the most
reliable current commercial bait harvest data by State. The
ASMFC requested that all States provide the Horseshoe Crab
Technical Committee with the most recent harvest data and
identify the reliability of the data. Based on the information
collected, the Horseshoe Crab Technical Committee reviewed and
approved the subject reference period landings. Several states
deferred to the NMFS harvest data; however, other states updated
harvest data based on state records. If multiple years of data
are available and reliable (e.g., harvest reporting was accurate)
between 1995 and 1997, data were averaged; however, some States
reported only one year of data (e.g., 1996) either due to
availability or reliability. The reference period landings may
be an underestimate of actual total landings, due to under-
reporting during the subject reference period. Comparison of
reference period landings and historical landings can be made by
referring to Section 1.3.2. of the Plan.
Table 3. Reference period landings for commercial bait harvest
of horseshoe crabs between 1995 - 1997.
--------------------------------------
---------------------------------
State Pounds Numbers Source
--------------------------------------
---------------------------------
Maine 300 112 NMFS (97 logbook1)
New Hampshire 803 300 NMFS
(96 logbook1)
Massachusetts 1,950 730 NMFS
(95-97 logbook1)
Rhode Island 490 184 NMFS
(96-97 logbook1)
Connecticut 1,494 560 NMFS
(95-97 logbook1)
New York 1,085,500 406,554
NMFS (95-97 logbook1)
New Jersey 2,381,229 604,049
State (96)2
Pennsylvania 0 0 State
(95-97)3
Delaware 2,065,764 482,401
State (95-97)2
Maryland 2,647,857 613,225
State (96)2
Virginia 62,070 23,247 State (96-
97)2
North Carolina 8,331 3,120 State
(95-97)3
South Carolina 0 0 NMFS
(95-97 landings4)
Georgia 0 0 NMFS
(95-97 landings4)
Florida 0 0 NMFS
(95-97 landings4)
________ _________
TOTAL 8,255,788 2,134,482
--------------------------------------
---------------------------------
1National Marine Fisheries Service (1998) Vessel Trawl Logbook
Data.
2State does require mandatory reporting of horseshoe crab
landings.
3State does not require mandatory reporting of horseshoe crab
landings.
4National Marine Fisheries Service (1998) Horseshoe Crab Landings
Data.
Source: National Marine Fisheries Service (1998) and individual
state harvest records. The Horseshoe Crab Technical
Committee reviewed and approved the reference period
landings based on the reliability and accuracy of the best
available data.
Note: The reference period landings may either be an average
of several years or an individual year depending on data
available. The Horseshoe Crab Technical Committee used the
NMFS conversion rate of 2.67 lbs / individual for NMFS data
and the following conversion rates for New Jersey and
Delaware (males, 2.32 lbs / individual; females, 5.12 lbs /
individual; both sexes, 3.72 lbs / individual). Maryland
used either 4 or 5 lbs / individual based on composition of
landings as determined by harvesters.
Several management options are available to maintain or curtail
current commercial bait harvest of horseshoe crabs. All
management options would include mandatory monitoring as
described in Section 3.5 of the Plan.
Option 1. Allow unrestricted harvest of horseshoe crabs (existing
state laws regarding horseshoe crab harvest would be at
the individual State's discretion). ASMFC would
conduct annual monitoring and recommend additional
management measures as needed.
Option 2. Establish a coastwide cap 25 percent below the
reference period landings from January 1 through
December 31, 1999. Harvest or landing of horseshoe
crabs between April 15 through June 15, 1999 shall be
prohibited.a
Option 3. Establish a coastwide cap 10 percent below the
reference period landings from January 1 through
December 31, 1999. Restrict the harvest of horseshoe
crabs to hand-harvest only between April 15 through
June 15, 1999, such that hand-harvest during this
period does not exceed 15 percent of the total
allocation for the State.a
Option 4. Establish a coastwide cap 50 percent below the
reference period landings from January 1 through
December 31, 1999. Harvest or landing of horseshoe
crabs between April 15 through June 15, 1999 shall be
prohibited.a
Option 5. Maintain existing state laws (e.g., New Hampshire, New
Jersey, Delaware, Maryland, Virginia, and South
Carolina) regarding horseshoe crab harvest, but add a
prohibition or phase-out of hand-harvest and establish
a coastwide cap not to exceed reference period
landings.
a Each state would be required to reduce harvest within its
jurisdiction by the subject threshold level. The Board would
review overharvest (i.e., overages) by states in any particular
year and could subtract the overages from subsequent harvest
thresholds. The closed harvest period (e.g., April 15 through
June 15) established under the FMP may be lengthened or
shortened, on an annual basis, following review by the Horseshoe
Crab Technical Committee and final approval by the Board.
Preferred Alternative: The Management Board has identified that
Option 2 is the preferred alternative. This alternative was
recommened by the Technical Committee. The preferred alternative
should ensure consistent management throughout the Atlantic Coast
and be sensitive to shifts in horseshoe crab harvesting to states
that currently have little or no management measures in place.
Additional management options that were considered by the
Management Board are identified in Appendix A.
Methods to maintain or reduce annual harvest (management options
2-15) include the following:
(a) Restrict the method of harvest (e.g., prohibit commercial
trawling and dredging, as required in New Jersey and
Virginia, limit hand-harvesting [particularly during the
breeding season], or other methods as needed). Restriction
imposed under this alternative must extend to federal
waters.
(b) Limit daily possession, catch, and / or landings (as
required in New Hampshire, Delaware, and Maryland). This
method of harvest restriction also could apply to specific
sexes.
(c) Limit harvest seasons or specific days of harvest (as
required in New Jersey, Delaware, and Maryland).
(d) Limit the location of authorized harvest (as required in New
Jersey, Delaware, and Maryland).
(e) Limit the number of potential harvesters (as required in New
Jersey, Delaware, and Maryland).
(f) Limit the landing of horseshoe crabs in state waters to
state-permitted harvesters.
These harvest restriction methods listed above could be combined
(similar to existing regulations in New Jersey, Delaware, and
Maryland) to achieve the desired management option. One method
of harvest restriction may be to prohibit or phase-out hand-
harvesting of horseshoe crabs and allow net, trawl, and dredge
harvesting. This would reduce the selective harvest of females
and the direct harvest of spawning horseshoe crabs. Net, trawl,
and dredge harvesting could be restricted to the fall after the
horseshoe crabs have spawned, thereby preventing disturbance of
shorebirds that feed on horseshoe crab eggs in the spring.
Regardless of what, if any, harvest restrictions are authorized,
all states must monitor and report the monthly and annual
commercial horseshoe crab harvest, including numbers, weight,
sex, and value.
4.2.2. Management Measures For Other Fisheries
The current estimate of commercial harvest for biomedical
applications is between 200,000 and 250,000 horseshoe crabs per
year on the Atlantic Coast (Swan, pers. comm., 1998, McCormick,
pers. comm., 1998). This harvest has increased from 130,000 in
1989 according to the FDA. The FDA and the South Carolina
Department of Natural Resources require the return of horseshoe
crabs to the environment. Most labs return bled crabs to their
habitat within 72 hours of capture (Botton, 1995). As many as
20,000 to 37,500 horseshoe crabs (10 to 15 percent) do not
survive the bleeding procedure. The reported 10 to 15 percent
may be a maximum bleeding mortality rate (Swan, pers. comm.,
1998; McCormick, pers. comm., 1998). However, the mortality
associated with collecting, shipping, and handling remains
unknown. Because both the number of horseshoe crabs captured
per year and the reported mortality are low, no harvest or
landing restrictions are currently recommended for the biomedical
industry. However, horseshoe crabs taken for biomedical purposes
should be returned to the same state or federal waters from which
they were collected. If horseshoe crab mortality associated with
collecting, shipping, handling, or use by the biomedical industry
exceeds 57,500 horseshoe crabs per year, the ASMFC would
reevaluate potential restrictions on horseshoe crab harvest by
the biomedical industry.
The use of horseshoe crabs for scientific and educational
research remains unreported; however, the number of horseshoe
crabs harvested for these purposes is considered to be small. No
harvest or landing restrictions are currently recommended for
scientific and educational research. If harvest or use of
horseshoe crabs for scientific and educational research increases
by a factor of two from current levels, the ASMFC would
reevaluate potential restrictions on horseshoe crab harvest and
use for such purposes.
4.2.3. Management Measures in Federal Waters
Harvest of horseshoe crabs in federal waters that are not landed
in states, but exchanged directly to a dependent fishery (e.g.,
conch fishers), must be evaluated. Therefore, to comply with the
selected management option, the ASMFC recommends that the
Secretary of Commerce address and initiate controls over harvest
and use of horseshoe crabs in federal waters that are not landed
in states.
4.3. HABITAT CONSERVATION AND RESTORATION
Protection of essential habitat such as spawning beaches is
critical to the continued survival of horseshoe crabs. Each
state must identify, categorize, and prioritize essential
horseshoe crab habitat (both spawning and nursery habitat) within
areas of its jurisdiction. Periodic monitoring must be designed
and implemented to ensure the long-term viability of critical
horseshoe crab spawning beaches.
As evidenced by erosion rates over the last 70 to 100 years,
beach erosion and limits on natural beach migration will continue
to threaten horseshoe crab essential habitat (U.S. Army Corps of
Engineers, 1991; U.S. Army Corps of Engineers, 1997; Thompson,
1998). Residential and commercial development adjacent to
critical horseshoe crab spawning habitat should be discouraged to
allow natural migration of beaches landward and to avoid
potential shoreline protection in the form of bulkheads,
revetments, and rip-rap. In areas where residential and
commercial development is adjacent to horseshoe crab spawning
habitat, remedial action (e.g., beach nourishment) should be
implemented in cooperation with agencies charged with shoreline
protection (e.g., U.S. Army Corps of Engineers and state coastal
engineering agencies) to ensure that critical spawning beaches
are not lost to coastal erosion.
Specifically, Section 1135(b) of the Water Resources Development
Act of 1986, as amended (33 U.S.C. 2201 et seq.; 100 Stat. 4082)
allows the U.S. Army Corps of Engineers (Corps) to investigate,
study, modify, and construct projects for the restoration of fish
and wildlife habitats where degradation is attributable to
existing federal water resources projects (e.g., dredging, groin
construction, bulkheads, seawalls) previously constructed by the
Corps. Additionally, Section 206 of the Water Resources
Development Act of 1996 (33 U.S.C. 2201 et seq.) allows the Corps
to investigate, study, modify, and construct projects for the
restoration of aquatic habitats, where degradation is not
directly attributable to an existing federal water resource
project.
Beach nourishment may restore or improve spawning habitat,
provided measures are implemented to minimize adverse project-
related impacts on horseshoe crabs and other resources.
Specifically, borrow areas for beach nourishment should be
located offshore to avoid adverse impacts on essential juvenile
habitat (nearshore, shallow water, subtidal flats). The grain
size of renourishment material should be similar in size to the
grain size that currently exists on the beach. Construction
activities should avoid critical spawning and juvenile
development periods. In the mid-Atlantic region, the generally
recommended seasonal restriction is from April 15 to August 30.
However, the specific seasonal restriction dates for any
particular area should be based on site-specific data and
appropriate monitoring.
States should consider obtaining land adjacent to critical
spawning beaches to ensure the long-term protection of these
beaches. Protection of essential habitat should be pursued
through acquisition, deed restrictions, or conservation
easements. In addition, states should pursue restricting all-
terrain vehicles and beach watercraft activity (e.g., jet skis)
on spawning beaches during the spawning season (with the
exception of emergency vehicles) to minimize mortality of
horseshoe crab embryos and larvae.
4.4. ALTERNATIVE STATE MANAGEMENT REGIMES
With approval of the Horseshoe Crab Management Board, a state may
vary its regulatory specifications contained in Section 4.2., so
long as that state can show to the Board's satisfaction that the
target fishing mortality will not be exceeded. Under no
circumstances will states be allowed to institute management
regimes that compromise the minimum number of horseshoe crabs
necessary to sustain dependent fish and wildlife resources.
Although additional data must be collected to accurately
determine the number of horseshoe crabs necessary to sustain
dependent fish and wildlife resources, the best scientific
information currently available must be used to ensure that
horseshoe crabs and their eggs are available to sustain fish and
wildlife resources.
4.4.1. Procedures
Procedures to modify state regulations include the following:
(a) A state may submit a proposal for a change to its regulatory
program or any mandatory compliance measure under the Plan
to the ASMFC. Changes shall be submitted to the ASMFC
staff, who will distribute the proposal to the Management
Board, the Plan Review Team, the Technical Committee, the
Stock Assessment Committee, and the Advisory Panel.
(b) States must submit a proposal at least two weeks prior to
the Technical Committee's spring or fall meeting.
(c) The Plan Review Team is responsible for gathering the
comments of the Technical Committee, the Stock Assessment
Committee, and the Advisory Panel, and presenting these
comments to the Management Board for action.
(d) The Management Board will approve the state proposal for an
alternative management program if it determines that the
alternative management program is consistent with the target
fishing mortality rate, and meets the goals and objectives
of this Plan.
4.4.2. De minimis Status
The ASMFC Interstate Fisheries Management Fisheries Program
Charter defines de minimis as "a situation in which, under
existing condition of the stock and scope of the fishery,
conservation, and enforcement actions taken by an individual
state would be expected to contribute insignificantly to a
coastwide conservation program required by a Fishery Management
Plan or amendment."
States may apply for de minimis status if, for the last two
years, their combined average commercial landings (by weight)
constitute less than one percent of coastwide commercial landings
for the same two-year period (for 1999 and 2000 reference period
landings will be used). States may petition the Board at any
time for de minimis status, if their fishery falls below the
threshold level. Once de minimis status is granted, designated
States must submit annual reports to the Board justifying the
continuance of de minimis status.
4.5. ADAPTIVE MANAGEMENT
Under adaptive management, the Horseshoe Crab Management Board
may vary the requirements specified in the Plan to achieve the
goals and objectives specified in Section 2. Specifically, the
Management Board may change target fishing mortality rates and
harvest restrictions. Such changes will be effective on January
1 (or on the first fishing day of the year), but may be put in
place on an alternative date when deemed necessary by the
Management Board.
Procedures to implement adaptive management are as follows:
(a) The Plan Review Team (PRT) will continually monitor the
status of the fishery and the resource and report to the
Management Board on or about March 15. The PRT will consult
with the Technical Committee, the Stock Assessment
Committee, and the Advisory Panel, in making their review
and report. The report will contain recommendations
concerning proposed adaptive revisions to the management
program.
(b) The Management Board will review the PRT report, and may
consult independently with the Technical Committee, the
Stock Assessment Committee, or the Advisory Panel. The
Management Board may direct the PRT to prepare an addendum
to affect changes it deems necessary. The addendum shall
contain a schedule for the states to implement its
provisions.
(c) The PRT will prepare a draft addendum as directed by the
Management Board, and shall distribute it to all states for
review and comment. A public hearing will be held in any
state that requests one. The PRT will also request comment
from federal agencies and the public at large. After a 30-
day review period, the PRT will summarize the comments and
prepare a final version of the addendum for the Management
Board.
(d) The Management Board shall review the final version of the
addendum prepared by the PRT, and also shall consider the
public comments received and the recommendations of the
Technical Committee, the Stock Assessment Committee, and
the Advisory Panel; it shall then decide whether to adopt or
revise the addendum.
(e) Upon adoption of an addendum, states shall prepare plans to
carry out the addendum and submit them to the Management
Board for approval, according to the schedule contained in
the addendum.
4.6. MANAGEMENT INSTITUTIONS
4.6.1. Atlantic States Marine Fisheries Commission and ISFMP
Policy Board
The ASMFC and the Interstate Fisheries Management Program (ISFMP)
Policy Board are responsible for the oversight and management of
the ASMFC's fisheries management activities. The ASMFC must
approve all fishery management plans and amendments thereto, and
must make final determinations concerning state compliance or
noncompliance. The ISFMP Policy Board reviews recommendations of
the various Management Boards and, if it concurs, forwards them
to the ASMFC for action.
4.6.2. Management Board
The Management Board is responsible for the development of a
fishery management plan or amendment. The Management Board shall
provide the ISFMP Policy Board with review and recommendations
based on the fishery management plan. The Management Board may,
after the necessary plan or amendment has been approved by the
ASMFC, continue to monitor the implementation and enforcement of
the fishery management plan or amendment, advise the ISFMP Policy
Board of its effectiveness, or take other actions specified in
the fishery management plan that are necessary to ensure its full
and effective implementation.
4.6.3. Plan Review Team
The PRT is a small group whose responsibility is to provide staff
support necessary to carry out and document the decisions of the
Management Board. The PRT is directly responsible to the
Management Board for providing information and documentation
necessary to carry out the Board's decisions.
4.6.4. Technical Committee
The Technical Committee will consist of one representative from
each jurisdiction and federal agency with an interest in the
horseshoe crab fishery. Its role is to act as a liaison to the
individual state agencies, providing information to the
management process and review and recommendations concerning the
management program. The Technical Committee will report to the
Management Board, normally through the PRT.
4.6.5. Stock Assessment Committee
The Stock Assessment Committee will consist of those scientists
with expertise in the assessment of horseshoe crab populations.
Its role is to assess horseshoe crab populations and provide
scientific advice concerning the implications of proposed
management alternatives, or to respond to other scientific
questions of the Management Board. The Stock Assessment
Committee will report to both the Management Board and the
Technical Committee.
4.6.6. Advisory Panel
The Horseshoe Crab Advisory Panel is established according to the
ASMFC Advisory Committee Charter. Members of the Advisory Panel
are citizens who represent a cross-section of commercial and
recreational fishing interests and others concerned about
horseshoe crab conservation and management. The Advisory Panel
provides the Management Board with advice directly concerning the
ASMFC's horseshoe crab management program. Normally, the
Advisory Panels meetings will be held at and in conjunction with
selected Management Board meetings.
4.6.7. Departments of Commerce and Interior
The ASMFC has accorded NMFS (Department of Commerce) and the
USFWS (Department of the Interior) voting status on the ISFMP
Policy Board and the Horseshoe Crab Management Board. These
federal agencies participate on the Plan Review Team, the
Technical Committee, and the Stock Assessment Committee.
5.0. COMPLIANCE
Upon completion and approval of a management plan, ASMFC states
are obliged to implement its requirements. If a state does not
comply with the conservation measures of the ASMFC fishery
management plan, the law allows the U.S. Secretary of Commerce to
impose a moratorium on that state's particular fishery. All
ASMFC fishery management plans must include specific measurable
standards to improve the status of the stocks and to determine if
the states comply with the standards.
5.1. MANDATORY COMPLIANCE ELEMENTS FOR STATES
A state will be found out of compliance if:
o its regulatory and management programs for horseshoe crab
have not been approved by the Management Board;
o it fails to meet any implementation schedule established or
any addendum prepared under adaptive management (see Section
4.5);
o it has failed to implement a change to its program when
determined necessary by the Management Board; or,
o it fails to adequately enforce any aspect of its regulatory
and management programs.
5.1.1. Mandatory Elements of State Programs
5.1.1.1. Regulatory Requirements
All state programs must include a regime of restrictions on
commercial fisheries consistent with the requirements of Section
4.2.; except that a state may propose an alternative management
program under Section 4.4. If approved by the Management Board,
the state's proposal may be implemented as an alternative
regulatory requirement for compliance under the law.
5.1.1.2. Monitoring Requirements
All state programs must include the mandatory monitoring
requirements contained in Sections 3.5 and 4.2 of the Plan.
States must submit proposals to the ASMFC for any intended
changes to the required monitoring programs if the change may
affect the quality of the data or the ability of the program to
fulfill the needs of the fishery management plan. State
proposals for modifications to required monitoring programs will
be submitted to the Technical Committee at least two weeks prior
to its spring or fall meetings. Proposals must be on a calendar
year basis. The Technical Committee will make recommendations to
the Management Board concerning whether the proposals are
consistent with the Plan.
If a state realizes it will be unable to fulfill its independent
fishery monitoring requirements, it should immediately notify the
ASMFC in writing. The ASMFC must be notified by the planned
commencement date of the monitoring program. The ASMFC will work
with the state to develop a plan to secure funding or to plan an
alternative program that will satisfy the needs outlined in the
Plan. If the Plan is not implemented within 90 days after its
adoption, the state will be found out of compliance with the
Plan.
5.1.1.3. Enforcement Requirements
All state programs must include law enforcement capabilities
adequate for successfully implementing the jurisdiction's
horseshoe crab regulations. The adequacy of a state's
enforcement activity will be measured by semi-annual reports to
the ASMFC Law Enforcement Committee and the PRT. Such reports
will be presented at the regular ASMFC spring and fall meetings,
and will follow the format shown in Figure 1. The first
reporting period will cover the period from January 1 to June 30
(report at the fall meeting), and the second period will extend
from July 1 to December 31 (report at the spring meeting).
5.1.2. State Reporting and Compliance Schedule
Each state must submit an annual report concerning its horseshoe
crab fisheries and management program on or before March 1 each
year, beginning March 1, 1999. The report shall cover:
(a) the previous calendar year's fishery and
management program, including activity and results of
monitoring (as identified in Section 3.5 of the Plan),
regulations that were in effect and harvest, including
estimates of nonharvest losses; and,
(b) the planned management program for the current
calendar year (summarizing regulations that will be in
effect and monitoring programs to be performed)
highlighting any changes from the previous year.
States must implement this Plan according to the following
schedule:
February 15, 1999: States must submit state
programs to implement the Plan for approval
by the Management Board. Programs, including
monitoring programs, must be implemented upon
approval by the Management Board.
March 15, 1999: States with approved
management programs may begin implementing
the Plan.
5.2. PROCEDURES FOR DETERMINING COMPLIANCE
A. The PRT will continually review the status of state
implementation of the Plan, and advise the Management Board
whenever a question arises concerning state compliance. The
PRT will review state reports submitted under Section 5.1.2.
and prepare a report by May 1 for the Management Board,
summarizing the status of the resource and fishery and the
status of state compliance on a state-by-state basis.
B. Upon receipt of a report from the PRT, or at any time by
request from a member of the Management Board, the
Management Board will review the status of an individual
state's compliance. If the Management Board finds that a
state's regulatory and management program fails to meet the
requirements of this section, it may recommend that the
state is out of compliance. The recommendation must include
a specific list of the state's deficiencies in implementing
and enforcing the Plan and the actions that the state must
take in order to come back into compliance.
C. If the Management Board recommends that a state is out of
compliance, as referred to in the preceding paragraph, it
shall report that recommendation to the ISFMP Policy Board
for further review according to the ASMFC Charter for the
Interstate Fisheries Management Program.
D. A state that is out of compliance or subject to a
recommendation by the Management Board under the preceding
subsection may request at any time that the Management Board
reevaluate its program. The state shall provide a written
statement concerning its actions to justify a reevaluation.
The Management Board shall promptly conduct such
reevaluation (e.g., within 30 days), and if it agrees with
the state, the Management Board shall recommend to the ISFMP
Policy Board that the determination of noncompliance be
withdrawn. The ISFMP Policy Board and the ASMFC shall
address the Management Board's recommendation according to
the ASMFC Charter for the Interstate Fisheries Management
Program.
Figure 1. Format for biannual law enforcement reports.
STATE_________________________Reporting
Period__________________19__
Contact
Person/Telephone_____________________________________________
_________________________________________________________________
_____
Enforcement Data:
1. Total Staff-Hours Horseshoe Crab
Enforcement_________________
2. Total Number of Inspections Made__________
3. Total Number of Complaints Received______________
4. Total Number of Enforcement Actions Taken:
a. Total Cases_____________
b. Total Warnings_____________
c. Total Revocations of Permits or Licenses_____________
5. Total Numbers of Horseshoe Crabs Seized_____________
_________________________________________________________________
______
II. Narrative Description: (Include for the commercial
fishery: current regulations; current levels of
participation and recent trends; general attitudes towards
regulations and their effectiveness; regulatory problems, if
any; recent large cases or major investigations.)
6.0. MANAGEMENT RESEARCH NEEDS
6.1. STOCK ASSESSMENT AND POPULATION DYNAMICS
In order to collect information to assist in future management
decisions, a comprehensive monitoring plan must be developed
throughout the Atlantic Coast as described in section 3.5. In
addition to the comprehensive monitoring plan, additional stock
assessment and population dynamics information should be
collected to assist in future management decisions including the
following:
(a) Conduct additional stock assessments and determine harvest
mortality rates (F). Use these data to develop a more
reliable sustainable harvest rate.
(b) Investigate larval and juvenile survival and mortality to
assist in the assessment of annual recruitment. Such
research could be aided by continuing and initiating new
tagging programs within individual states.
(c) Further evaluate life table information including sex ratio
and population age structure.
(d) Formulate a coastwide benthic sampling program for horseshoe
crabs using standardized and statistically robust
methodologies (including equipment appropriate to collect
adult horseshoe crabs [e.g., benthic sled]). Survey cost,
agency responsibility, schedule for implementation must
also be identified for the subject coastwide horseshoe crab
benthic sampling programs.
(e) Determine if geographic subpopulations exist, which may have
implications for management.
6.2. RESEARCH AND DATA NEEDS
(a) Investigate, encourage, and fund alternative bait sources
(e.g., artificial bait) for eel and conch fisheries.
Implement any alternative bait sources to reduce the need
for commercial horseshoe crab harvesting. Alternative bait
sources are currently being investigated by Nancy Targett
(University of Delaware Graduate College of Marine Studies).
(b) Conduct economic studies to determine the value of the
commercial fishery, biomedical, and ecotourism industries
and the impact of regulatory management on these industries.
(c) Evaluate the effect of mosquito control chemicals on
horseshoe crabs to determine impacts from such activities on
horseshoe crab populations.
(d) Determine the relationship between horseshoe crab egg
abundance and body condition, nutrient intakes, fecundity,
and survival of dependent shorebirds (e.g., shorebird blood
sample research as proposed by Barboza and Jorde).
(e) Continue or initiate shorebird surveys using standardized
methodologies to determine weight gain during stopovers,
shorebird habitat use as it relates to horseshoe crab
essential habitat (e.g., shorebird numbers as it relates to
horseshoe crab egg densities), population trends, and if
possible a population estimate.
(f) Determine beach fidelity by horseshoe crabs to determine
habitat use.
(g) Evaluate the effectiveness of currently used trawl gear for
stock assessment.
(h) Evaluate the impacts of beach nourishment projects on
horseshoe crab populations.
7.0. REFERENCES
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trilobite larvae of the horseshoe crab, Limulus polyphemus,
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_____, L.J. Niles, and J. Burger. 1993. Abundance and
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_____ and L.J. Niles. 1997. Unpublished data. New Jersey
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aerial shorebird survey of Delaware Bay. Records of New
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spawning activity on Delaware Bay shores 1990. Finn-Tech
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effects on development and early posthatch stages of
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appendices.
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turtles in Virginia. Copeia 1985(2):449-456.
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7.2. PERSONAL COMMUNICATIONS
Babey, G. 1997. Fisheries Biologist. Fisheries Division,
Connecticut Department of Environmental Protection.
Hartford, Connecticut.
Breese, G. 1998. Senior Staff Biologist. Delaware Bay Estuary
Project, U.S. Fish and Wildlife Service. Smyrna, Delaware.
Coates, P. 1997. Director of Marine Fisheries. Massachusetts
Department of Fisheries, Wildlife, and Environmental Law
Enforcement. Boston, Massachusetts.
Colvin, G. 1997. Director. Division of Marine Resources. New
York Department of Environmental Conservation. East
Setauket, New York.
Cupka, D. 1998. Director. Office of Fisheries Management,
Marine Resources Division, South Carolina Department of
Natural Resources. Charleston, South Carolina.
Daniel, L. 1997. Biologist Supervisor. Division of Marine
Fisheries, Department of Environment and Natural Resources.
Morehead City, North Carolina.
Evans, C. 1997. Marine Resource Specialist. Coastal Resources
Division, Department of Natural Resources. Macon, Georgia.
Evans, J. 1998. Aquatic Pathobiologist. Stranding Coordinator,
Fisheries Service, Maryland Department of Natural
Resources. Oxford, Maryland.
Himchak, P. 1997. Fisheries Biologist. Division of Marine
Fisheries, New Jersey Department of Environmental
Protection. Trenton, New Jersey.
Maney, R. 1997. Fisheries Program Specialist. State and
Federal Constituents Office, National Marine Fisheries
Service, National Oceanic and Atmospheric Administration.
Gloucester, Massachusetts.
Manus, A. 1998. Director. Division of Fish and Wildlife,
Department of Natural Resources. Dover, Delaware.
McCormick, W.M. 1998. Bio-Whittaker, Incorporated.
Walkersville, Maryland.
Michels, S.F. 1997. Fisheries Scientist. Division of Fish and
Wildlife, Department of Natural Resources. Dover, Delaware.
Nelson, J. 1997. Chief. Division of Marine Fisheries. New
Hampshire Fish and Game Department. Durham, New Hampshire.
O'Connell, T. 1997 and 1998. Fisheries Biologist. Maryland
Department of Natural Resources, Fisheries Service.
Annapolis, Maryland.
Rudloe, A. 1998. Professor / Researcher. Florida State
University. Tallahasee, Florida.
Shuster, C.N., Jr. 1995. Adjunct Professor. Virginia Institute
of Marine Science, College of William and Mary.
Williamsburg, Virginia.
Sisson, R. 1997. Deputy Chief of Marine Fisheries. Division of
Fish and Wildlife, Department of Environmental Management.
Wakefield, Rhode Island.
Snyder, R. 1998. Division Chief. Division of Fisheries
Management, Pennsylvania Fish and Boat Commission.
Harrisburg, Pennsylvania.
Sorksen, M. 1997. Marine Patrol Officer. Maine Department of
Marine Resources. Augusta, Maine.
Swan, B.L. 1998. Director. Limuli Laboratories. Dias Creek,
Cape May County, New Jersey.
Travelstead, J. 1997. Chief of Fisheries Management Division.
Virginia Marine Resources Commission. Newport News,
Virginia.
Vale, V. 1997. Chief of the Office of Fisheries Management.
Division of Marine Resources, Florida Department of
Environmental Protection. Tallahassee, Florida.
APPENDIX A
Additional Management Options For Bait Fisheries Considered By
The Management Board
Options 1 through 5 are identified in Section 4.2.1. of the Plan.
Option 6. Establish a moratorium on the commercial harvest of
horseshoe crabs for one year. Continuance of such a
moratorium would be evaluated on a yearly basis based
on stock status. States would reopen fisheries upon
approval of ASMFC.
Option 7. Maintain existing state laws (e.g., New Hampshire, New
Jersey, Delaware, Maryland, Virginia, and South
Carolina) regarding horseshoe crab harvest and
establish a coastwide cap not to exceed reference
period landings.
Option 8. Establish a coastwide cap not to exceed reference
period landings.
Option 9. Establish a coastwide cap 10 percent below the
reference period landings from January 1 through
December 31, 1999. Harvest or landing of horseshoe
crabs between April 15 through June 15, 1999 shall be
prohibited.a
Option 10. Establish a coastwide cap 75 percent below the
reference period landings from January 1 through
December 31, 1999. Harvest or landing of horseshoe
crabs between April 15 through June 15, 1999 shall be
prohibited.a
Option 11. Establish a coastwide cap of 10 percent below the
reference period landings.a
Option 12. Establish a coastwide cap of 25 percent below the
reference period landings.a
Option 13. Establish a coastwide cap of 50 percent below the
reference period landings.a
Option 14. Establish a coastwide cap of 75 percent below the
reference period landings.a
Option 15. Maintain existing state laws (e.g., New Hampshire,
New Jersey, Delaware, Maryland, Virginia, and South
Carolina) regarding horseshoe crab harvest, but add a
prohibition against harvesting between February and
July and establish a coastwide cap not to exceed
reference period landings.
aEach state would be required to reduce harvest within its
jurisdiction by the subject threshold level. The Board would
review overharvest (i.e., overages) by states in any particular
year and could subtract the overages from subsequent harvest
thresholds. The closed harvest period (e.g., April 15 through
June 15) established under the FMP may be lengthened or
shortened, on an annual basis, following review by the Horseshoe
Crab Technical Committee and final approval by the Board.
HORSESHOE CRAB SPECIES PROFILE
TABLE OF CONTENTS
I. SPECIES TAXONOMY AND MORPHOLOGY 49
II. LIFE HISTORY CHARACTERISTICS OF THE HORSESHOE CRAB 49
A. SPATIAL AND SEASONAL DISTRIBUTION BY LIFE STAGE 49
B. ENVIRONMENTAL REQUIREMENTS 50
C. SPAWNING 51
D. FEEDING AND GROWTH 53
E. SOURCES OF NATURAL MORTALITY 54
1. Predation 54
2. Diseases and Parasites 55
3. Stranding 56
III. REFERENCES 57
A. LITERATURE CITED 57
B. PERSONAL COMMUNICATIONS 60
I. SPECIES TAXONOMY AND MORPHOLOGY
Horseshoe crabs (Limulidae) are currently represented by four
extant species including Limulus polyphemus found along the
eastern coast of North and Central America and three Indo-Pacific
species, Tachypleus tridentatus, T. gigas, and Carcinoscorpius
rotundicauda (Shuster, 1982). One Asiatic species (Tachypleus
tridentatus) is threatened in parts of its range due to
overfishing, spawning habitat loss, and coastal pollution (Finn
et al., 1991; Botton, 1995). All four species are similar in
terms of ecology, morphology, and serology. Shuster (1955)
identified that serological data from three of the four extant
species indicates that the species are not congeneric (i.e., from
the same genus). The following life history characteristics and
discussion of horseshoe crabs will focus on Limulus polyphemus.
Horseshoe crabs are benthic (or bottom-dwelling) arthropods that
use both estuarine and continental shelf habitats. Although it
is called a "crab," it is neither a decopod or crustacean, rather
horseshoe crabs are grouped in their own class (Merostomata),
which is more closely related to the arachnids (Shuster, 1982).
Horseshoe crabs have persisted for more that 200 million years
(Botton and Ropes, 1987); however, Shuster (1996) identifies the
evolutionary existence of horseshoe crabs to be over 400 million
years.
Horseshoe crabs exhibit sexual dimorphism. Males are generally
smaller than females at maturity (probably a result of females
undergoing one more molt than males), with mean prosomal widths
75-79 percent of the adult female mean prosomal widths (Shuster,
1982). In addition, males have claspers that aid in attaching to
females during amplexus (i.e., males coupled to females).
Shuster (1979) suggested that each major estuary along the coast
had a discrete horseshoe crab population, which could be
distinguished from one another by adult size, carapace color, and
eye pigmentation. However, no significant differences between
the morphologic characteristics of discrete populations are
evident, based on high variability both within and among
populations (Riska, 1981). In addition, based on
electrophoretic evidence, gene flow does occur between widely
separated populations, although considerable genetic variation
exists within and between populations of horseshoe crabs
(Selander, et al., 1970). Saunders et al. (1986) found no
evidence for genetic divergence between New England and middle
Atlantic populations based on mitochondrial DNA analysis. Larger
animals and populations are located in the middle of the species'
distribution (Maryland to New York) while smaller animals and
populations are found in the southern and northern extent of its
range (Shuster, 1982). Based on morphometric data collected in
South Carolina, Thompson (1998) suggests that the greatest mean
adult horseshoe crab size occurs in the South Atlantic Bight and
decreases in size north and south. Thompson (1998) hypothesized
that larger individuals occur in the South Atlantic Bight due to
optimal temperature and salinity for horseshoe crab development
in this region.
II. LIFE HISTORY CHARACTERISTICS OF THE HORSESHOE CRAB
A. SPATIAL AND SEASONAL DISTRIBUTION BY LIFE STAGE
Horseshoe crab distribution extends along the Atlantic coast from
northern Maine (42oN) to the Yucatan Peninsula (19oN) and the
Gulf of Mexico (Shuster, 1982). Horseshoe crabs are abundant
between Virginia and New Jersey, with Delaware Bay at the center
of the species distribution and the location of the largest
population (Shuster and Botton, 1985; Botton and Ropes, 1987).
Within Delaware Bay, the largest concentration of horseshoe crabs
is found along the Cape May shore of New Jersey (Shuster and
Botton 1985). Spawning densities of over 30 animals per meter
occur within the Delaware Bay, based on 1986 spawning counts
along 15 meter segments (Botton, et al., 1988). Horseshoe crab
populations are smaller north of Cape Cod and south of Georgia,
and individuals are smaller in size. The largest horseshoe crabs
are found in estuaries from Georgia to New Jersey (Shuster,
1979). Spawning densities in Florida and South Carolina were
reported as three and one animal per meter, respectively (Rudloe,
1980; Thompson, 1998). Even in New Jersey and Delaware,
horseshoe crab abundance decreases with distance north and south
of the Delaware Bay (Botton and Haskin, 1984).
Adult horseshoe crabs feed in coastal estuaries and along the
Atlantic Coast throughout the summer. Adults either remain in
the estuary or migrate to the continental shelf during the winter
months. Migration is reinitiated in the spring, when horseshoe
crabs move to beach areas to spawn. Juveniles hatch from the
beach environment and spend the first two years in shallow,
subtidal, flats near shore.
Horseshoe crab populations are typically associated with
estuarine habitats. Important estuaries that support horseshoe
crabs include Narragansett Bay in Rhode Island; Plum Island
Sound, Cape Cod Bay, and Vineyard and Nantucket Sounds in
Massachusetts; Long Island Sound in New York; Delaware Bay in New
Jersey and Delaware; Chesapeake Bay in Maryland and Virginia;
Beaufort Inlet in North Carolina; and, numerous estuaries within
the South Atlantic Bight and Gulf Coast of Florida (Shuster,
1979; Rudloe, 1980).
Adult horseshoe crabs have been found as far as 35 miles offshore
and in depths of over 290 meters (Botton and Ropes, 1987).
However, 74 percent of the total number of horseshoe crabs caught
in bottom trawl surveys compiled by the Northeast Fisheries
Center were taken in water shallower than 20 meters and 92
percent were caught at depths less than 30 meters. Migration
from beaches where horseshoe crabs have been tagged vary from a
few kilometers in Florida to almost 34 kilometers in
Massachusetts (Shuster, 1982). Horseshoe crabs remain dispersed
over the continental shelf and on bay bottoms (e.g., Delaware Bay
and Chesapeake Bay) for most of the year (Botton, 1995).
However, trawl surveys in South Carolina found horseshoe crabs
present on the continental shelf only during spring through fall.
No animals were collected offshore during the summer trawling
session (Thompson, 1998).
Based on a tagging and recovery program, Rudloe (1980) concluded
that the mean distance travelled from a breeding beach in Florida
was 7.6 kilometers with a range of 3.5 and 40.7 kilometers.
Similarly, Shuster (1950) reported tagged horseshoe crab
movements of up to 33.8 kilometers in Cape Cod Bay,
Massachusetts. Thompson (1998) reported maximum distance covered
by a tagged horseshoe crab was 4 kilometers in South Carolina.
However, distance traveled may reflect movement of a fishing
vessel rather than actual animal migration (Thompson, 1998).
B. ENVIRONMENTAL REQUIREMENTS
The distribution of horseshoe crabs is chiefly defined by water
temperature, salinity, and depth, with temperature as a limiting
factor for northern ranges (Shuster, 1982). Horseshoe crabs are
ecological generalists and can survive within a wide range of
environmental conditions. Horseshoe crabs are tolerant of a wide
range of salinities; however, low salinities (<4 ppt) are lethal
(Pearse, 1928). The horseshoe crab is also tolerant of a wide-
range of oxygen levels. Physiological changes in the blood
enable the horseshoe crab to survive hypoxic conditions on the
continental shelf and when partially buried during spawning and
in hyperoxic conditions when exposed to air (Shuster, 1982).
Optimal salinities from fertilization to hatching are in the
range of 20 to 30 ppt; however, salinities of <20 ppt and >30 ppt
significantly prolong development. Temperature also has a
significant effect on development. Embryonic development and
time required to hatch is positively correlated with temperature;
development occurs more rapidly in warmer temperatures (i.e.,
35oC) than colder temperatures (i.e., 20oC) (Jegla and Costlow,
1982).
Horseshoe crab larvae and embryos are characterized by extreme
tolerance to hypoxic conditions, although embryos are slightly
more tolerant to hypoxia than larvae. Development appears to
stop at the onset of hypoxic conditions and resumes when normoxic
conditions resume (Palumbi and Johnson, 1982). Currently, there
are no data to suggest unusual sensitivity by horseshoe crabs to
low dissolved oxygen, high turbidity, or urban or agricultural
pollution (Botton, 1995).
C. SPAWNING
Migrating adults move inshore from deep bay and coastal waters in
late spring to spawn. Inshore movement appears to be related to
lengthening daylight hours. Spawning in the Chesapeake and
Delaware Bays usually begins during the latter part of May when
large numbers of horseshoe crabs move onto beaches to mate and
lay eggs. The peak in spawning activity usually coincides with
the high tide during the full moon and new moon in May and June
in Delaware and New Jersey. However, in Florida breeding
activity continues between March and November with peak spawning
occurring as early as April (Brockmann, 1990) and as late as late
August (Rudloe, 1980). In Massachusetts, spawning occurs between
May and July (Barlow et al., 1986). Breeding activity is
consistently higher during the full moon than the new moon and is
also greater during the night as compared with the day tide
(Rudloe, 1980). Thompson (1998) also found a significantly
higher rate of spawning during the night in South Carolina.
Thompson (1998) found that spawning horseshoe crabs responded to
optimum tidal and solar conditions available during each lunar
phase, rather than lunar phase itself. Barlow et al. (1986) in
Massachusetts and Penn and Brockmann (1994) in Delaware found
spawning activity greatest during the highest tides regardless of
whether it was day or night. Brockmann and Penn (1992) found a
significant tendency for horseshoe crabs tagged during the day to
return to spawn during the day, while horseshoe crabs tagged
during the night to return to spawn during the night. Lunar
cycle, day of the year, and wave height are significantly
correlated with horseshoe crab spawning activity (Rudloe, 1980).
As a result of the high cost of spawning (i.e., mortality)
Shuster and Botton (1985) observed that horseshoe crabs avoid
spawning during rough weather, apparently overriding the impact
of lunar periodicity.
Spawning activity is significantly greater at water temperatures
of 20o C or greater in South Carolina (Thompson, 1998). At
temperatures below 20o C, a state of dormancy is initiated and
production of ecdysone is curtailed, which inhibits molting and
development (Jegla, 1982).
While current tagging studies in New Jersey and South Carolina
have not discounted the possibility of spawning site fidelity,
horseshoe crabs are probably not loyal to one spawning site over
successive years and generations (Thompson, 1998). However,
spawning animals do display short-term fidelity to a spawning
site, and return to the same site on numerous high tides until
spawning is complete (Thompson, 1998; Brockmann, 1990). Shuster
(1994) reports that while horseshoe crabs probably do not return
to their natal beaches, a majority do return to the same estuary
to spawn.
Adults prefer sandy beach areas within bays and coves that are
protected from surf although spawning has been observed on mud,
sod, and peat banks. In addition, horseshoe crabs may be capable
of spawning in subtidal areas (Rudloe, pers. comm., 1998). Such
low energy embayments include Tom's Cove (Chincoteague Bay,
Virginia), Sandy Hook Bay (New Jersey), and Great Bay (New
Hampshire) (Botton and Loveland, 1989). Optimum spawning areas
are limited by the availability of sandy beach habitat. Eggs are
laid in clusters or nest sites along the beach, usually between
the tide marks. The average number of eggs per cluster is
approximately 3,650 to 4,000 (Shuster 1982; Shuster and Botton,
1985)). Several egg clusters are made during one beach trip and
females will return on successive tides to lay more eggs. A
female will lay about 20 egg clusters each season in the Delaware
Bay (Botton, 1995). However, Brockmann (1990) only identified up
to 15 egg clusters each season in Florida. Fecundity, the total
number of eggs per female per year, is approximately 88,000
(Shuster, 1982). Density of egg clusters has been reported to be
as high as 50 egg clusters / linear meter (Shuster and Botton,
1985) and up to 500,000 eggs/m2 (Botton et al., 1994). Egg
development is dependent on temperature, moisture and oxygen and
usually takes a month or more.
Egg nests are located in a broad area between 3 meters from the
low-water line to the spring high-tide line (Shuster, 1982).
Geochemical characteristics of the beach are more relevant than
distance downslope or elevation (Penn and Brockmann, 1994).
There are differences in the distribution of egg nests within a
beach, which may be dependent (in part) upon the amplitude of the
tides and beach morphology (Shuster, 1982; Penn and Brockmann,
1994). Specifically, beach morphology (e.g., grain size) affects
oxygen, temperature, and moisture gradients on the beach.
Delaware Bay beaches are characterized as coarse-grained and well-
drained, whereas Florida beaches are fine-grained and poorly
drained (Penn and Brockmann, 1994). Since horseshoe crabs nest
at beach elevations where egg development is maximized, Penn and
Brockmann (1994) found the mean nesting location for horseshoe
crabs on Delaware Bay beaches to be about equal to the mean high
tide line. However, horseshoe crabs in Florida nest much higher
up on the beach (than in the Delaware Bay) to avoid anaerobic
conditions at the mean high tide line (Penn and Brockmann, 1994).
Ultimately, eggs buried too high on the beach are subject to
desiccation and those buried too low are subject to anoxic
conditions (i.e., insufficient interstitial oxygen
concentrations). Eggs are deposited in clusters in the upper
portion of the intertidal zone. Depth of eggs in the sediment
range from 5 to 20 centimeters below the surface (mean 11.5 + 2.8
centimeters) (Rudloe, 1979; Brockmann, 1990). The mean nest
depth in Delaware was found to be 9.3 + 3.9 centimeters (Penn and
Brockmann, 1994).
In Massachusetts, New Jersey, and Delaware, horseshoe crabs often
spawn during neap tides (Penn and Brockmann, 1994; Cavanaugh,
1975; Barlow et al., 1986). However, in Florida, horseshoe crabs
almost never spawn during neap tides (Rudloe, 1980). Penn and
Brockmann (1994) conclude that the dissimilarity is due to
differences in grain size (aerobic sediments occur at higher
elevations in Florida than in Massachusetts, New Jersey, and
Delaware). Additionally, neap tides are lower in Florida and
flood tides rarely reach the aerobic zone of the beach,
explaining why horseshoe crabs in Florida do not nest during neap
tides (Penn and Brockmann, 1994).
Horseshoe crab reproductive success is greatest under the
following conditions: (1) the egg clusters are moistened by
water with salinity of at least 8 parts per thousand; (2) the
substrate around the egg clusters is well oxygenated; (3) tides
are sufficient to keep incubating eggs moist; (4) the beach
surface is exposed to direct sunlight to provide sufficient
incubation; and, (5) the slope of the beach is adequate for
larvae to orient and travel downslope to the water upon hatching
(Shuster, 1994).
Penn and Brockmann (1994) found that horseshoe crabs in Delaware
tended to place their nests in sand that was about 3 percent
saturated. Eggs that were buried above this zone were more
likely to desiccate. The saturated sediments of the lower beach
contained insufficient interstitial oxygen concentrations for egg
development to occur. Moisture content of the sediment is
related to grain size. The grain size of the beaches that had
the greatest horseshoe crab spawning concentrations, as reported
by Shuster and Botton (1985), had grain sizes of from 0.5 to 2.0
mm in diameter (Botton et al. 1994), with a medium grain size of
0.7 mm. Beaches used by spawning horseshoe crabs in South
Carolina and Florida have much smaller grain sizes. In South
Carolina, grain sizes on study beaches used by horseshoe crabs
are between 0.2 and 0.4 mm (Thompson, 1998).
The mechanism by which horseshoe crabs locate preferred spawning
habitat is not completely understood. While horseshoe crabs
spawn in greater numbers and with greater fecundity along sandy
beaches, horseshoe crabs can tolerate a wide range of physical
and chemical environmental conditions, and will spawn in less
suitable habitats if ideal conditions are not encountered.
Therefore, the presence of large numbers of horseshoe crabs on a
beach is not necessarily an indicator of habitat suitability
(Shuster, 1994). It is known that shoreline areas with high
concentrations of silt or peat are less favorable to horseshoe
crabs, because the anaerobic conditions reduce egg survivability.
It also appears that horseshoe crabs can detect hydrogen sulfide,
which is produced in the anaerobic conditions of peat substrates,
and that horseshoe crabs actively avoid such areas (Botton et
al., 1988; Thompson, 1998). Jacobsen (pers. comm., 1996)
believes that horseshoe crabs need at least 8 inches of sand over
peat to occur to avoid anaerobic conditions that could prevent
egg development, with 16 inches or more being optimal.
Beach slope is also thought to play an important role in
determining the suitability of beaches for horseshoe crab
spawning (Shuster, pers. comm., 1995). Horseshoe crabs generally
travel downslope after spawning and appear to become disoriented
on flat areas (Jacobsen, pers. comm., 1995). Field experiments
by Botton and Loveland (1987) determined that beach slope is more
significant than vision in orientation behavior and identified
poor orientation performance on flat beaches. Horseshoe crabs
show rapid seaward orientation on beaches with slopes of
approximately 6 degrees (Botton and Loveland, 1987). Although
the optimal beach slope is unknown, beaches commonly used by
horseshoe crabs in New Jersey have slopes of between 3 and 7
degrees to seaward (U.S. Fish and Wildlife Service, 1995).
Jacobsen (pers. comm., 1996) estimates the optimal slope to be
about 7 percent. However, Thompson (1998) concluded that while
parameters controlling site selection for spawning would normally
favor beaches with an optimal slope (i.e., gentle seaward slope),
beach slope itself is not likely to be the determining parameter
selected by spawning horseshoe crabs.
Erosion is also an important component in spawning success.
Erosion of the substrate in which eggs are deposited would
increase egg and larval mortality. Thompson (1998) suggested
that short-term, seasonal erosion characteristics may be more
important than long-term conditions.
In addition to the intertidal zone used for spawning, horseshoe
crabs also use shallow water areas (less than 12 feet deep) such
as intertidal flats and shoal water as nursery habitat for
juvenile life stages. Adult horseshoe crabs forage in deep water
habitat during most of the year, except during the breeding
season when they move into shallow and intertidal water.
The presence of offshore intertidal flats may also influence the
use of certain beaches by spawning horseshoe crabs. Horseshoe
crabs may congregate on intertidal flats to wait for full moon
high tides, because these flats provide protection from wave
energy. Thompson (1998) identified that preferentially selected
spawning sites were located adjacent to large intertidal sand
flat areas. In addition to providing protection from wave
energy, sand flats typically provide an abundance of available
food for juvenile horseshoe crabs. Since several tidal cycles
may be required to complete spawning, offshore intertidal flats
may provide safe areas to rest between tide cycles.
D. FEEDING AND GROWTH
Overcrowding or high-density egg clusters delay the time of
hatching for horseshoe crabs (Barber and Itzkowitz, 1982).
However, typically eggs hatch between 14 and 30 days after
fertilization (Sekiguchi, et al., 1982; Jegla and Costlow, 1982;
Botton, 1995). The optimum temperature for egg development has
been estimated at between 30o and 35o C (Jegla and Costlow,
1982). Larvae emerge from the egg capsule and swim for a period
of approximately 6 days. Larvae typically settle in shallow
water areas after the free-swimming period to molt (Shuster,
1982). Larvae molt into the first juvenile instar approximately
20 days after emergence (Jegla and Costlow, 1982).
Some "trilobite" larvae delay emergence and overwinter within
beach sediments, emerging the following spring (Botton et al.,
1992). This was observed during the winters of 1989 to 1992 and
included densities of between 1,000/m2 and 10,000/m2 of live
trilobites in sediment depths greater than 15 centimeters.
Overwintering larvae emerge in March and April the following year
after spending 8 months in beach sediment. This phenomenon is
reported in New Jersey and Massachusetts (Botton et al., 1992).
While overwintering in beach sediment does risk mortality
associated with erosion from coastal storms, the strategy does
minimize avian predation and provides insurance in the event
previous cohorts had poor survivorship (Botton et al., 1992)
Upon hatching, the larvae are motile and spend about 6 days
swimming until they settle to the bottom and molt. Larvae move
to the sand surface and emerge at spring high tide on full-moon
nights in Florida; however, larvae are also released during
storms with heavy surf (Rudloe, 1979). Larvae do not emerge
during spring high tides (associated with the new moon) and
appear to be nocturnally active (Rudloe, 1979). Although the
free-swimming period provides the possibility of wide dispersion,
most larvae settle in shallow, intertidal areas near the beaches
where they were spawned. Juvenile horseshoe crabs generally
spend their first and second summer on the intertidal flats,
usually near breeding beaches (Rudloe, 1981; Shuster, 1982).
Thompson (1998) found significant use of sand flats by juvenile
horseshoe crabs in South Carolina. Older crabs move out of
intertidal areas and are found a few miles offshore except during
breeding migrations (Botton and Ropes, 1987). After larval
stages leave the beach environment, horseshoe crabs do not return
to the beach until they are sexually-active adults (Rudloe,
1979).
The horseshoe crab must molt, or shed its chitinous exoskeleton,
to grow. Molting occurs several times during the first two to
three years. As the horseshoe crab grows larger, more time
exists between molts. Horseshoe crabs usually take at least 16
to 17 molts to reach sexual maturity over a period of 9 to 11
years (Shuster, 1950). However, the often cited age of sexual
maturity is based on a series of exuviae from a single captive
specimen. Females reach maturity one year later than males and,
consequently, go through an additional molting stage (Shuster,
1955).
Once sexual maturity is reached, horseshoe crabs no longer molt
(or molt rarely) and can live an additional 8 years based on
growth of epifaunal slipper shells (Crepidula fornicata) on the
horseshoe crab prosoma (Botton and Ropes, 1988). Therefore,
longevity for horseshoe crabs may be at least 17 to 19 years in
the northern part of their range, accepting the estimate of 9 to
11 years to reach sexual maturity (Shuster, 1950).
Horseshoe crabs swim or crawl as their primary means of
locomotion. Both larvae and juveniles are more active at night
than during the day (Rudloe, 1979; Shuster, 1982: Thompson,
1998). Juveniles typically feed prior to the daytime low tide,
then burrow into the sand, remaining inactive during the
remainder of the day (Rudloe, 1981; Thompson, 1998). Because
horseshoe crabs lack jaws, they crush and pulverize food using
the spiny bases of their legs, then move the food into the mouth.
Larvae feed on a variety of small polychaetes, nematodes, and
nereis (Shuster, 1982). Juvenile and adult horseshoe crabs feed
mainly on molluscs, including razor clam (Ensis spp.), macoma
clam (Macoma spp.), surf clam (Spisula solidissima), blue mussel
(Mytilus edulis), wedge clam (Tellina spp.), and fragile razor
clam (Siliqua costata); however, horseshoe crabs also prey on a
wide variety of benthic organisms including arthropods, annelids,
nemertean, and polychaete worms (Botton, 1984; Botton and Haskin,
1984). In the Delaware Bay, horseshoe crabs prefer soft-shell
clam (Mya arenaria) and small surf clam (Mulinia lateralis) over
gem clam (Gemma gemma) despite the numerical dominance of the gem
clam in the Delaware Bay (Botton, 1984). The horseshoe crab is
also an important predator of soft-shell clams in Massachusetts.
Shuster (1950) reported horseshoe crabs consuming sand worm
(Nereis spp.), sand ribbon worm (Cerebratulus spp.), gem clam,
macoma clam, razor clam, and soft-shell clam in Cape Cod Bay,
Massachusetts. Botton (1984) found 56.4 percent of prey was
infaunal burrowers, which included bivalves and polychaetes.
Botton (1984) also found vascular plant material in nearly 90
percent of all individuals. Botton and Ropes (1989) hypothesized
that horseshoe crabs may control species diversity, richness, and
abundance in areas where they prey upon small molluscs and
polychaetes. No differences between diet and food preference are
apparent between male and female horseshoe crabs. Shuster (1996)
identified that food for the horseshoe crab (e.g., bivalves,
molluscs, and marine worms) are abundant on the continental shelf
in areas where horseshoe crabs abound.
E. SOURCES OF NATURAL MORTALITY
1. Predation
Most eggs survive to hatching (Rudloe, 1979). However, Loveland
et al. (1996) identify that mortality is extensive among eggs and
larvae. Eggs and larvae are preyed upon by macroinvertebrates
including sand shrimp (Crangon septemspinosa), blue crab
(Callinectes sapidus), green crab (Carcinus maenas), and spider
crab (Libinia spp.) (Shuster, 1982). Finfish also eat eggs and
larvae including striped bass (Morone saxatilis), white perch
(Morone americana), American eel (Anguilla rostrata), killifish
(Fundulus spp.), silver perch (Bairdiella chrysoura), weakfish
(Cynoscion regalis), kingfish (Menticirrhus saxatilis),
silversides (Menidia menidia), summer flounder (Paralichthys
dentatus), and winter flounder (Pleuronectes americanus)
(Shuster, 1982). Shorebirds also feed on horseshoe crab eggs
including semipalmated plover (Charadrius semipalmatus), black-
bellied plover (Pluvialis squatarola), red knot (Calidris
canutus), pectoral sandpiper (Calidris melanotos), least
sandpiper (Calidris minutilla), semipalmated sandpiper (Calidris
pusilla), dowitcher (Limnodromus spp.), sanderling (Calidris
alba), ruddy turnstone (Arenaria interpres), and laughing gull
(Larus atricilla). The willet (Catoptrophorus semipalmatus) is
also a predator of horseshoe crab eggs and larvae (Rudloe, 1979).
Adult horseshoe crabs provide food for sharks (Squaliformes),
gulls (Larus spp.), and boat-tailed grackles (Quiscalus major)
(Shuster, 1982). In addition, adult and juvenile horseshoe crabs
make up a portion of the loggerhead sea turtle's (Caretta
caretta) diet in the Chesapeake Bay (Musick, et al. 1983).
Shuster (1996) also identifies red fox (Vulpes vulpes) and
raccoon (Procyon lotor) as potential predators of adult and
juvenile horseshoe crabs. Despite potential predation, Loveland
et al. (1996) identify that natural mortality among subtidal
adults is probably low. However, horseshoe crab predation
mortality from sea turtles and other marine animals remains
unknown.
Between the 1850s and the 1920s, over 1 million horseshoe crabs
were harvested annually for fertilizer and livestock feed
(Shuster, 1982; Shuster and Botton, 1985). Reported harvests in
the 1870s were 4 million horseshoe crabs annually, and 1.5 to 1.8
million horseshoe crabs annually between 1880s and 1920s (Finn et
al., 1991). Shuster (1960) reports that in the late 1920s and
early 1930s 4 to 5 million crabs were harvested annually.
Shuster (1960) reports over 1 million crabs were harvested during
the 1940s and 500,000 to 250,000 horseshoe crabs were harvested
in the 1950s. By the 1960s, only 42,000 horseshoe crabs were
reported to be harvested annually (Finn et al., 1991). More
recently horseshoe crabs have been taken in substantial numbers
to provide bait for other fisheries, including (primarily) the
American eel and conch (Busycon carica and B. canaliculatum)
fisheries. Horseshoe crabs, particularly females, are cut up and
placed in American eel pots as bait. The conch fishery uses
horseshoe crabs of either sex. Horseshoe crabs are also
collected by the biomedical industry to support production of
Limulus Amebocyte Lysate. However, this industry bleeds
individuals and releases the animals live after the bleeding
procedure. Approximately 10 to 15 percent of animals do not
survive the bleeding procedure (Rudloe, 1983; Thompson, 1998).
2. Diseases and Parasites
Bacterial infection of horseshoe crabs may adversely affect
individual horseshoe crabs. Infection may be caused by erosion of
the carapace or injuries. Triclad flatworms and cyanobacteria
have caused extensive gill pathology within horseshoe crabs
(Groff and Leibovitz, 1982).
External parasites and ectocommensals do not commonly attach to
horseshoe crabs due to the frequency of molting (Shuster, 1982).
However, Thompson (1998) and Rudloe (pers. comm., 1998) identify
that the Bdelloura candida flatworm is common on horseshoe crab
gills and appendages, but is not known to be parasitic. A
variety of other marine organisms including mussels, gnathobases,
barnacles, and other sessile organisms may attach to horseshoe
crabs. These species may be harmful if they attach to the
ventral surface and interfere with feeding or locomotion
(Shuster, 1982). Internal parasites such as the metacercariae
may cause intense and massive internal infections (Shuster,
1982).
Horseshoe crabs may share a commensal relationship with pinfish
(Lagodon rhomboides) and juvenile blue crabs (Callinectes
sapidus). The pinfish and blue crab stay in close proximity to
horseshoe crabs feeding on particles of detritus and small
organisms stirred into the water column from the "ploughing"
action of horseshoe crabs (Rudloe, 1985).
3. Stranding
Botton and Loveland (1989) identified that at least 190,000
horseshoe crabs died from beach stranding along the New Jersey
shore of the Delaware Bay during the 1986 spawning season (May to
June). This represents nearly 10 percent of the adult horseshoe
crab population and is considered a substantial source of natural
mortality. Rudloe (pers. comm., 1998) identifies that stranding
mortality in Florida may be much lower based on personal
observations. Natural mortality was estimated by Swan (pers.
comm., 1998) to be up to 8 percent based on a mark and recapture
study where 860 individuals were tagged. Stranded crabs
typically succumb to factors such as hyperthermia, osmotic
imbalance, excessive energy expenditure during spawning,
desiccation, and predation by large predators (such as gulls)
(Botton and Loveland, 1989). Entrapment in man-made structures
such as rip-rap, bulkheads, and jetties also accounts for
mortality. Telson abnormalities is related to beach stranding,
because broken or shortened telsons prohibit crabs from righting
themselves, resulting in stranding (Botton and Loveland, 1989).
Stranding is also related to mating tactics and righting ability
in male horseshoe crabs. Unattached males are more likely to
become stranded than attached males because they do not have the
larger female as an "anchor." Additionally, on average, older
males are more likely to become stranded than younger males
probably due to senescence and parasitism (Penn and Brockmann,
1995).
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