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SCIENCE FILE

After Eons, Troubling Signs

The Once-Plentiful Horseshoe Crab Is Declining, and Shorebirds Wane With It

July 04, 1996|JAMES GERSTENZANG | TIMES STAFF WRITER

HEISLERVILLE, N.J. — Day after day, century after century, eon after eon, the lowly horseshoe crab has been crawling out of shallow waters to lay its eggs in the muck and sand of bayside beaches.

"The horseshoe crabs are dinosaurs," observes Albert Engle, manager of Bidwell Creek Marina. No, he says, on second thought: "They're pre-dinosaurs. Nothing'll kill them."

Well, not exactly.

A hatchet will do nicely. So will an ax. Even a butcher's band saw.

All are used in a springtime frenzy of chopping and hacking as the crabs, their blood turning blue when exposed to air, are quartered by the truckload for use as bait.

On a really good day here, when the sun is just coming up and the full moon is setting, the crabs come crawling across the washed-out road to Thompson's Beach, deposited there by the high tide in Delaware Bay at the northern edge of Cape May.

It is on these days, says Mike Litchko, that he and three companions, donning hip waders and rubber gloves, can grab 2,000 crabs--some weighing as much as 15 pounds--and toss them into a refrigerated truck. Before the day is half over, Litchko's work is done and the crabs are on their way--fetching 60 cents for an egg-laden female--to bait traps that put conch fritters on Florida menus and turn eels into sushi.

At least that's the way the business has worked so far.

Now, the mottled brown creature--resembling a battle-scarred Darth Vader helmet trailing a frightening but harmless spike-like tail--may be disappearing from its home in the waters of Delaware Bay.

One survey shows the horseshoe crab population down dramatically; another suggests a more modest, steady decline. The total crab count, certainly in the millions, cannot be determined precisely.

Neither can the cause of the decline. No one is certain whether over-harvesting, pollution or loss of habitat to natural causes or development is to blame. All could have played a part.

The situation has become worrisome enough that New Jersey recently imposed limits on the annual harvest. No crabs can be caught by hand on the sandy beaches, and dredging by boat is prohibited too. Crab stalkers must confine their efforts to designated inland estuaries two days a week during the May spawning period.

No matter how many crabs have actually been lost--or why--the future of a creature long seen as offering little of value besides baiting the traps of commercial fisherman reaches beyond the economics of a cottage industry.

In small amounts, the crab's blood is drawn--with no harm to the animal--by laboratories for use in detecting endotoxins, potentially fatal poisons that bacteria can release in the human bloodstream.

In large numbers, its eggs feed more than 1 million migrating shorebirds barely larger than robins. To them, the reduced number of crabs is potentially a significant threat.

The birds refuel along the beaches here and in Delaware each spring during their flight from South America to the Canadian Arctic--the most important feeding stop for the hemisphere's migratory birds outside of Alaska.

If the crabs disappear, so do their eggs--and so will the ruddy turnstones, red knots, sanderlings and semipalmated sandpipers that they feed, if not to extinction, then to other locales in search of food.

The crabs, members of the arachnid family that includes spiders and scorpions, have been tested before. They have survived every change the environment has thrown their way since a period 150 million years before there were dinosaurs.

Carl N. Shuster Jr. of the Virginia Institute of Marine Sciences at the College of William and Mary, who has been a student of horseshoe crabs for nearly half a century, estimates that the current population is about 25% of its maximum, which he believes was reached in the 1870s.

"The animal pretty much attacks the environment broadside. Whatever nature presents, it will try to survive in. It's able to survive in a wide range of parameters--temperature, salinity, depth," he said.

The crabs spend the summer, autumn and winter within the bay's waters. Once they reach maturity at the age of about 10, female crabs spend the next decade or so depositing an average of 88,000 eggs every spring on the bay's beaches. Sometimes as many as five or six males will hitch a ride on a female's back, fertilizing the eggs in the sand before retreating to the bay. The eggs may hatch within two weeks, incubated by the sun, but some will survive in the sand until spring.

Along come the birds.

Delaware Bay has become critical in their migration, says Brian Harrington, author of "Flight of the Red Knot" and naturalist at the Manomet Observatory on the shores of Massachusetts Bay.

"The way shorebirds migrate is to feed at an area with a high production of food, and it has to be predictable," he said. "There are not many places where they can do their refueling on the northbound migration."

Harrington notes that about 85% of the species that traverse the Western Hemisphere stop at Delaware Bay.

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