Horseshoe Crab Population May Be on Rebound

CAPE MAY — The poor, upside down horseshoe crab lying on the beach, kicking its five pairs of legs in the air while trying to turn itself over before it becomes a meal for a seagull, is not a pretty sight but the creature that has been around for 455 million years is wanted by more than just the birds.
Horseshoe crabs are sought by fisherman as the primary bait for conch, whelk and eels. The crab’s blood is used in the biomedical industry to test injectable drugs and vaccines for toxins.
Excessive harvesting of horseshoe crabs diminished their numbers but stringent regulations may be creating a stable population. In March 2008, Gov. Jon Corzine signed legislation imposing a moratorium on harvesting horseshoe crabs in New Jersey.
Over-harvesting of horseshoe crabs has led to a diminished supply of food for birds called red knots and has brought the species to the brink of extinction. Miraculously they arrive at exactly the time of year when the horseshoe crabs are laying eggs on the beach.
Red knots fly from as far south as Tierra Del Fuego, off the Chilean coast, non-stop to Delaware Bay where they feed on horseshoe crab eggs before flying to the artic to breed. Birds that do not put on significant weight during their stop along our bay do not survive the trip to the arctic.
This state’s horseshoe crab harvesting moratorium will remain in place until the populations of both horseshoe crabs and red knots have returned to a level where they will be self sustaining as determined by the U.S. Fish and Wildlife service.
As part of the third annual Delaware Estuary Science and Environmental Summit Jan. 12, held here at the Grand Hotel, six scientists discussed preserving the horseshoe crab that does much more than feed migrating birds with its eggs.
Roy Miller, fisheries administrator with the Delaware Division of Fish and Wildlife, Department of Natural Resources and Environmental Control, said since 1989, his agency has used a 30-foot bottom trawl in Delaware Bay on a monthly basis to monitor the adult and juvenile horseshoe crab population. Horseshoe crabs are tagged and their migration studied.
Beginning in 1998 when management of horseshoe crabs began, Delaware’s harvest quota was 482,000 crabs. It was subsequently been lowered to 362,000, 150,000 and 100,000 horseshoe crabs, said Miller.
He said there was a considerable build up of crabs in their trawl survey in 2004 and then a decrease in 2006 and 2007. There was a considerable decline in population from 1990 to mid 1990’s.
A trawl survey by Virginia Tech, which works the ocean area just outside Delaware Bay, found a positive trend in the horseshoe crab population.
Miller said red knots declined through 2003 with some recent stabilization of the population at a relatively low level in the 12,000 to 15,000 range from both sides of Delaware Bay.
In Delaware, a harvest of just male horseshoes crabs is permitted only after June 8 of the year to allow shorebirds undisturbed access to crab eggs. Female horseshoe crabs cannot be harvested at any time, said Miller.
The maximum harvest in Delaware is 100,000 crabs per year, he said.
James F. Cooper addressed the biomedical use of horseshoe crab blood. He directed the first commercial development of Limulus Amoebocyte Lysate (LAL), which was accepted in 1991 by the FDA as the standard test for endotoxcins in injectable drugs and vaccines.
Cooper said horseshoe crabs are bled in a “clean room” and then returned to the bay alive and well. LAL replaced drug testing where rabbits were injected to see if they developed a fever within 48 hours indicating contaminants.
He said the global market for horseshoe crab blood was relatively small, about $100 million. A half million crabs per year are needed for the medical industry, said Cooper.
Less horseshoe crab blood may be need by the drug industry in the future as new methods require less blood using software driven instrumentation.