Real Birds
Shorebird Crisis: The Horseshoe Crabs of Delaware Bay

by Don Crockett



Table of Contents

Update: Summer 1998

Original Summer 1997 Article

Of Crabs and Birds and Decline by Pete Dunne

Overview
Life History of the Horseshoe Crab
Shorebird Migration and the Delaware Bay
Harvesting of Horseshoe Crabs
Horseshoe Crab Surveys
Shorebird Surveys
What's Being Done and What You Can Do
Links, Acknowledgements, and References



Overview

So what has happened to get Pete Dunne, as he describes in the introductory piece, so frustrated and upset.

Back in the early 80's, Pete was among the first to document and describe the spectacular concentrations of shorebirds that were gathering along the shores of the Delaware Bay from mid-May to early-June (Wander & Dunne, 1981). Each year half a million to a million or more shorebirds arrive on the bayshores to feast on the eggs of the largest concentration of spawning horseshoe crabs along the Atlantic coast. Many of the shorebirds use this abundant supply of food to fuel the last thousand miles of their northward migration to the artic tundra. Red Knots, for example, arrive below their fat-free weight after flying 7,000 miles from southern Brazil. The knots need to double their weight during their 2-3 week stay in order to complete their journeys to artic Canada and breed successfully (Harrington, 1996).

Several years ago Pete and others noticed that the numbers of shorebirds and crabs seemed to be in decline. This seemed all too closely related to the increase in harvesting of the crabs as bait for the eel, whelk, and conch fisheries. Surveys that had first been performed in 1990 & 1991 to determine the density of available eggs for birds on New Jersey beaches, showed a 90% decrease when performed in 1995 & 1996. Censuses of spawning crabs showed a 2/3 decrease from 1990 to the present with most of the decline attributed to fewer crabs on the New Jersey beaches. Trawl samples performed in the bay showed a decline that correlated closely with the census data. Despite regulations put into place to restrict how and when horseshoe crabs could be harvested, the numbers of crabs taken each year in New Jersey kept increasing.

And then this year the numbers of spawning crabs and shorebirds plummeted in New Jersey. What had once been an awe inspiring spectacle that lined the shores with layers of shorebirds and horseshoe crabs was reduced to small isolated groups. Surface egg density surveys confirmed that there were very few eggs available for shorebirds. Aerial surveys of the bay found that birds that in previous years had been evenly distributed around the bay were heavily concentrated around one section of the Delaware side of the bay, the only place where crabs had spawned in large numbers.

The dramatic effects witnessed this year are not necessarily solely based on harvesting pressure. Environmental factors such as water temperature and the lunar cycle could also have influenced when and where crabs spawned this year. Shifts in the percentages of crabs on the Delaware and New Jersey shores have been documented in the past. No one knows for sure at this point what is causing the changes. Surveys do show that there has been a significant decline in the horseshoe crab population in the bay, and the commercial harvest is the most significant and controllable source of mortality in the horseshoe crabs.

Based on the dramatic changes observed this spring, a 60-day moratorium banning the harvest of horseshoe crabs in New Jersey was put into effect on May 31st by Governor Christine Todd Whitman. Several birding and conservation organizations are urging that a total emergency ban on horseshoe crabs be put in place in NJ, DE, MD, and VA until comprehensive regulations can be developed and put into place to ensure the sustainability of the crabs and the shorebirds that depend on them. On July 29th, Governor Whitman announced new strict regulations and extended the ban until the regulations could be put in place.

Regulatory processes will be influenced by public opinion and you can help by contacting people involved in making the decisions and letting them know that you support regulations that will protect horseshoe crab populations and the shorebirds that depend on them.

While every attempt was made to accurately portray the current situation and research findings, inaccuracies may have been included in this article. References to formal publications are provided for people interested in pursuing this issue further.

Next: Life History of the Horseshoe Crab
Table of Contents


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