Harvesting of Horseshoe Crabs

The Horseshoe Crabs of Delaware Bay

Harvesting of Horseshoe Crabs

Heavy harvesting of horseshoe crabs in Delaware Bay goes back more than 150 years. During the 1800's, records show that over 4 million crabs were taken each year. The horseshoe crabs during this period were dried, ground up, and used as fertilizer and as food for livestock. By the 1920's the catch had declined to less than 2 million crabs and as the stocks of crabs were depleted in the 1940's and 1950's the large harvests stopped. The advent of chemical fertilizers reduced the demand for horseshoe crabs at about the same time.

Note: The above graphs show horseshoe crab landings in pounds. The average weight of a horseshoe crab is from 3-4 pounds. The numbers shown in the graphs are the reported landings and underestimate total landings. The numbers for 1996 are preliminary and do not include all landings reports.

After the heavy commercial harvest ended, the horseshoe crab population started to rebound. Significant harvesting of horseshoe crabs did not begin again until 1976. Horseshoe crabs were now being used as bait in American Eel pots (as well as for bait for conch and whelk). Depleted stocks of eels in the over harvested fisheries in Europe and Asia were replaced by harvests along the Atlantic states in the U.S. This created increased demand for bait for eels. Clam bellies had been used as bait and were inexpensive since they were an unused by-product of clam processing. But the clam industry switched to using enzymes to dissolve the clam bellies rather than removing them whole. Currently horseshoe crabs are used exclusively as bait in eel pots and the number of crabs taken each year has been growing at a rapid rate.

The eel bait fishery prefers female horseshoe crabs with eggs, since like shorebirds, eels are particularly attracted by the eggs. The ovaries of the female crab are spread throughout the prosoma in an extensive network and for most of the year the ovaries are filled with full-sized eggs (88,000 on average for crabs around the Delaware Bay). The preference of females by the crabbers is most significant during spawning when hand harvesters will just collect females as the crabs come in to shore to lay their eggs. Horseshoe crabs are also harvested by trawling and dredging throughout most of the year both in the Delaware Bay and the Atlantic Ocean.

Note: The crashed population of horseshoe crabs during the middle of the century may explain why the large concentrations of shorebirds were not discovered along the Delaware Bay until the early 1980's. One could speculate that the concentrations did not exist earlier this century since there are no written accounts of them. Without large numbers of horseshoe crabs and their eggs, the shorebirds may have spread out over other areas along the Atlantic coast. Another factor could be a reduced number of shorebirds earlier this century. During the 1800's market hunting of shorebirds wiped out large populations. (The shorebirds behavior of concentrating during migration made them easy targets for the shot gun.) This does not mean that the current number of shorebirds could find adequate alternate sources of food if the horseshoe crabs in Delaware Bay continue to decline. Development has reduced suitable wetlands and beaches along the Atlantic coast.

Given what happened earlier this century when heavy harvesting depleted the stocks of horseshoe crabs, the harvest trends shown in the graphs above raise concerns. The next section, Horseshoe Crab Surveys, presents data that show that this concern is warranted.

The Horseshoe Crabs of Delaware Bay