Lure of horseshoe crabs

Bait: As the stock of the creatures used in conch and eel harvesting dwindles, scientists in Delaware are working on an inexpensive synthetic version of a compound found in the creatures.


LEWES, DEL. -- In a small laboratory about 200 yards from the largest horseshoe crab spawning ground in North America, Nancy Targett, a University of Delaware biochemist, is working on a formula to ease the fishing pressure on the helmet-shaped creatures.

Targett and her students have figured out what it is about the female horseshoe crab that makes it such good bait for eel and conch. Now they have to figure out how to reproduce it synthetically in a form that will stand up to salt water at a price that commercial fishermen can afford.

Because of an exploding market for eel and conch in Europe and Asia, horseshoe crabs are being fished in record numbers for bait. The harvest on the Atlantic coast more than quadrupled from 1993 to 1996, according to a study by the Atlantic States Marine Fisheries Commission.

Until Delaware restricted its horseshoe crab harvest last year, fishermen freely walked the beaches of Delaware Bay during the spawning season and scooped up hundreds of females as they laid their eggs, or trawled for them in the waters just off the coast.

The fishermen hacked the females in quarters and dropped them in conch and eel pots. Or they sold them for $1 to $1.50 each.

Before the restrictions were ordered, "You could make a lot of money from the horseshoe crab," says Targett, associate dean of the university's graduate college of marine studies.

Horseshoe crabs, limulus polyphemus in scientific terms, were on Earth 100 million years before the dinosaurs. Despite their name, they are more closely related to spiders and scorpions than to the Atlantic blue crab.

They live most of their lives in the waters of the Continental Shelf from Maine to the Gulf of Mexico, but every year, as the days grow longer, they migrate to shore to spawn.

Nowhere do they spawn in greater numbers than on the narrow beaches of Delaware Bay, which from mid-May to mid-June look as if they have been paved with cobblestones. The crabs come ashore at the new and full moons, when the tides are highest, to mate and bury fertilized eggs in the sand. One female can lay about 90,000 eggs a year, according to a University of Delaware study.

The stock has dwindled in recent years, as the Atlantic States Marine Fisheries Commission noted in a December 1998 report. Spawning surveys in Delaware Bay and New Jersey have shown sharp declines, as have egg counts in New Jersey.

The commission concedes that strict scientific evidence of a decline is sketchy, but says that is mostly because of differences in reporting methods.

"We're here at the epicenter of the world for limulus, and there are indications of decline," says Targett.

Historically, horseshoe crabs have been used as food and by farmers as the original slow-release fertilizer in fields on the Delmarva peninsula.

Native Americans used their tails as spear tips and their shells to bail canoes.

Chitin from their shells is used for sutures and to make sheets for burn victims. Their blood is used in biomedical testing. Their eggs provide food for shore birds on their annual migration from the southern tip of Argentina to the Canadian Arctic to breed.

But most of the horseshoe crab harvest is used for bait -- 90 percent, according to Rick Robins of Chesapeake Bay Packing in Newport News, Va., the largest conch exporter in the United States.

Faced with evidence of declining populations of horseshoe crabs, New Jersey, Delaware and Maryland reduced their harvests by 60 percent to 80 percent during the past two years. But Virginia set a limit for this year that is 26 times higher than its average annual take and came under sharp criticism last month from U.S. Secretary of the Interior Bruce Babbitt and conservation groups.

Targett, who studies the chemical signals given off by marine creatures, began her work more than two years ago.

"We had a horseshoe crab symposium here, and I was listening to a lot of user groups talking about decline, and one guy said there is something in the female that attracts conch and eel," she recalls. "Well, that's right up my alley. I can do something about this."

She and an honors undergraduate student began with slices of male and female horseshoe crabs on opposite branches of a Y-shaped trough, with seawater and mud snails in the stem. Mud snails are related to conch, but they are easier to deal with in the lab, and scientists had noted that snails were attracted to horseshoe crabs on beaches.

Sure enough, the mud snails went for the females. So Targett and her students began the painstaking process of elimination to discover what causes the attraction.

Targett is a few steps away from being able to synthesize the compound and bring it to market, but the product is already drawing interest from fishermen and seafood processors.

"I'll be happy when it's out," says John Boland, a seafood buyer for Cape May Foods in Cape May, N.J. "We're looking at supplies of bait, anyway. Now, we're trying something from Maine that doesn't have to be frozen. It's a byproduct of processing fish."

One problem with using horseshoe crabs for bait is finding a place to store them. Jack LeCates, 63, a waterman from Rehoboth, Del., fills freezers with horseshoe crabs to keep them from spoiling.

"I don't know about the size of the stock, [but] horseshoe crabs are getting expensive and hard to find," he says. "If a lure is reasonably priced, and it works, it would be worth it."

Pub Date: 7/01/99

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