Census to check for decline in horseshoe crabs

The horseshoe crab evolved 100 million years before the dinosaurs and is closely related to spiders and scorpions.

June 21, 1999
Web posted at: 4:14 p.m. EDT (2014 GMT)

Scientists and volunteers are tallying the number of spawning horseshoe crabs at beaches along the Delaware Bay this month to determine whether their populations are dwindling.

The world's largest population of horseshoe crabs scrambles from the ocean to their spawning grounds on the Delaware Bay from the end of May until the end of June. Anecdotal evidence indicates their numbers are declining, probably as a result of over-harvesting and loss of habitat. But until now, no official research has been conducted.

"There has been a volunteer survey since 1990 but it was not designed to be statistically valid. The groups (involved in the census) are trying to come up with a statistically valid approach that's impartial so the agencies are not arguing about data but about what to do for the crabs," said Dr. David R. Smith, a U.S. Geological Survey biologist and statistician with the Leetown Science Center.

The census is being conducted at eight beaches in New Jersey and eight beaches in Delaware as part of a multi-state, university and federal project.

The horseshoe crab evolved 100 million years before the dinosaurs and is closely related to spiders and scorpions. This ancient creature is important to the medical community, commercial fishermen and the environment.

From a medical viewpoint, scientists have learned a lot about the human eye by studying the horseshoe crab's large compound eyes. Extracting a clotting agent called Limulus Amoebocyte Lysatefrom horseshoe crab blood is a multi-million dollar industry. LAL is used to test for the presence of gram-negative bacteria in human blood; in addition, all commercially produced intravenous drugs are tested for bacterial contamination using LAL.

Extracting LAL from the crabs is usually not fatal. Commercial fishermen who use the horseshoe crab as bait when harvesting conch and American eel are far more threatening, the scientists say.

From an ecosystem point of view, the protein-saturated egg of the horseshoe crab is a food staple to millions of migratory shore birds, many small fish and the threatened loggerhead turtle.

Although causes remain unknown, research has suggested that populations of certain migratory shorebirds are in serious decline. Biologists are studying whether a reduction in horseshoe crab eggs is linked to the declining numbers.

"It's clear that we need to know more about horseshoe crab status and trends," said Smith.

Preliminary results of the survey will be reported at the Aug. 31 meeting of the American Fisheries Society. The final report is scheduled for the end of the year.

Copyright 1999, Environmental News Network, All Rights Reserved