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Horseshoe crabs have roamed the planet for 450 million years, but they could be running out of time

Conservationists say the practice of catching the crabs, bleeding them for the unique chemical that detects toxic contamination, and then returning them to sea results in far too many of them dying.

A tagged horseshoe crab spawned at Reeds Beach in Cape May Court House, N.J., on June 13.Matt Rourke/Associated Press

One of the great delights of summer on the New England shore is catching sight in shallow waters of the humble horseshoe crab. Ancient and mysterious, these creatures are precious beyond their eerie beauty because their blood is essential to testing the safety of vaccines and medical equipment, and their nutrient-rich eggs provide food for endangered shorebirds such as the red knot.

But the horseshoe crab, surviving for at least 450 million years, is today imperiled by exploitation, both from commercial biomedical firms and from eel and whelk fishermen who use them for bait. Although scattered populations have rebounded, some — including the American horseshoe crab — are listed as endangered or vulnerable to extinction on the International Union for Conservation of Nature’s Red List of threatened species.


“For an animal that’s been around so long, who are we to usher them out?” said Deborah Cramer, whose book, “The Narrow Edge,” chronicles the crab’s importance to the red knot.

Last month, the Massachusetts Division of Marine Fisheries issued new regulations for horseshoe crab harvesting, including the first biomedical quota of 200,000 crabs. The state also lowered the cap on harvesting for bait, to 140,000 crabs per season. Government wildlife managers seek to balance the needs of various constituencies, including commercial interests, against the conservation of critical species. But given their essential role both in human health and coastal biodiversity, you have to ask why the state allows the taking of any horseshoe crabs for bait.

The situation is complicated by a patchwork of regulations. New Jersey, South Carolina, and Connecticut prohibit taking horseshoe crabs for bait. Other states, such as those abutting Delaware Bay, ban harvesting female crabs. In Massachusetts, harvesting is prohibited in limited areas such as the Monomoy National Wildlife Refuge in Chatham and the Cape Cod National Seashore. Many states prohibit harvesting everywhere during spawning season.


This year, the Massachusetts Audubon Society advocated for a spawning ban from January through May — expanding the current limits, which prohibit harvesting for five days around every full moon and new moon from April 16 to June 30. But that proposal was rejected by the Marine Fisheries Advisory Commission, which has authority over any regulatory changes affecting fishing interests in Massachusetts. Not coincidentally, strict protections in other states increase the pressure to harvest more crabs here.

But conservationists say the current practice of catching the crabs, bleeding them for the unique chemical — limulus amebocyte lysate — that detects toxic contamination, and then returning them to sea results in far too many of them dying. This summer The Trustees of Reservations added its name to Mass Audubon and others calling for the state to revisit the spawning ban and phase out the bait harvest altogether.

In an interview, Division of Marine Fisheries Director Dan McKiernan defended the state’s regimen, saying horseshoe crab stocks in Massachusetts are healthy enough to allow for some to be taken for bait, especially since whelk fishermen participate in a curious Massachusetts program called Rent-a-Crab, whereby they use crabs that already have been bled by biomedical firms. But given that DMF itself has said the channeled whelk population in Massachusetts is depleted, it seems odd to encourage more overfishing by providing this source of bait.


McKiernan added that DMF is constantly monitoring populations, and he is open to bringing tighter regulations before the the Marine Fisheries Advisory Commission in the future. “We do take the conservation of this species seriously,” he said, “and our approach is evolving.”

Despite — or perhaps because of — its prehistoric origins, the horseshoe crab has been a gold mine for scientific research. In the 1960s, biologists at the Woods Hole Oceanographic Institution found that horseshoe crab blood clots upon encountering endotoxin bacteria, providing a sensitive and fast way to test for contamination in vaccines and medical devices. Since testing with limulus amebocyte lysate was far superior to the previous method of using live rabbits, an entire industry of hunting horseshoe crabs was born. Every year some 750,000 crabs are bled for LAL, and by the most conservative estimate, at least 15 percent — over 100,000 — do not survive.

Given the intense scrutiny on the practice, pharmaceutical companies are working to find a synthetic alternative to LAL. Eli Lilly has been working with a cloned alternative called Recombinant factor C. Progress on this solution has been slow because of federal regulatory hurdles. But just this week, US Pharmacopeia — the body that determines how drugs are tested in the United States — issued a new standard that could allow for non-animal lysate alternatives similar to those used in Europe and Japan, pending further review.


It’s a promising development, but will it come soon enough to stop depleting horseshoe crab stocks? These wondrous creatures roamed the planet 200 million years before the dinosaurs, but they could be running out of time.

Renée Loth’s column appears regularly in the Globe.