The next time you take medicine, are hooked up to a hospital I.V., get
an organ transplant, or have a hip replaced, you can thank the horseshoe crab.
A component of the blood of the horseshoe crab has verified that those items
are free of dangerous toxins. Nothing else known to man can do that job as effectively.
Virginia Tech is returning the favor by helping to conserve the lowly,
ugly critter from the dinosaur era. In the most recent phase of fisheries
and wildlife professor Jim
Berkson's ongoing study of horseshoe crab populations, graduate student
Beth Walls spent the summer at Chincoteague monitoring the horseshoe crab population
along the Maryland/Virginia coast. She tagged crabs that will provide future
information on their movement and survival.
The status of the horseshoe crab population has generated a great deal
of interest in recent years (July 3, 1999 issue of U.S. News & World
Report) because they are used for bait to catch American eel, whelk, and
catfish.
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A Marylander used to boating
on the Chesapeake Bay, Beth Walls spent the summer hauling in horseshoe
crabs (sometimes 800 — 1100 per day), recording their age (based
on the condition of the shell) and sex, and tagging a portion of them.
The fisheries and wildlife graduate student traveled to Hampton, Va.,
every two weeks to place 20 crabs that had been bled and 20 crabs that
had not in an aquaculture tank at Virginia Tech’s Seafood Research
and Extension Center to monitor post-bleeding mortality.
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Berkson hopes his work will lead to better management practices and resolve
some of the conflicts medical interests have with commercial fishermen.
Horseshoe crabs have been used for biomedical research since the early
1900’s. Since the 1970’s they have been caught, bled, and released
alive to obtain Limulus Ameobocyte Lysate (LAL), a clotting agent used to detect
the presence of toxins pathogenic to humans in injectable drugs and all implantable
medical devices.
Today the LAL test is the standard test for screening medical equipment
for toxin contamination. If LAL clots in water surrounding the medical item,
that indicates that drug, IV, or body-part replacement is contaminated with
toxins and should not be used. The crabs' blood, by the way, is blue.
The FDA estimates that 260,000 horseshoe crabs were caught and bled for
the biomedical industry in 1997, compared with130,000 in 1989. Berkson and his
graduate student have been comparing the survival rate of crabs that have been
bled to crabs that have not been bled to estimate the mortality associated with
the bleeding process.
Previous studies have estimated the mortality rate to be less than 15 percent
after release. The commercial fishing industry catches substantially more crabs
than the biomedical industry and inflicts a substantially higher mortality rate
on the crabs. As part of the Atlantic States Marine Fisheries Commission’s
management plan of 1998, biomedical companies are required to tag a proportion
of the crabs they take for bleeding and estimate mortality rates involved in
the bleeding process.
BioWhittaker, the largest producer of LAL in the country, has asked Berkson
and Virginia Tech to conduct this research on its behalf. The research program
will also collect demographic data, including size, sex, and approximate age,
information critically needed to improve the management of the horseshoe crab
fishery.
If the horseshoe crab population continues to decline in the absence of
coordinated, coastwide monitoring and fishery regulations, the biomedical industry
and all users of the horseshoe crabs would be affected.
Lynn Davis
College of Natural Resources
Virginia Tech On Campus | Virginia
Tech Research Division | Virginia Tech
