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Horseshoe crabs are landing – the spawn is on

The ancient arachnid is on the rebound – so why isn’t the bird that depends upon it?

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Faith Zerbe, monitoring director of the conservation nonprofit Delaware River Keeper Network, has called it a "magical experience to stand in the dark and watch these creatures from 400 million years ago stream up out of the water.”

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Hall began his annual census in 1991. Volunteers arrived in the hundreds to save the crab – people like Glenn Gauvry, a conservationist with an affection for the limulus who organized a group to defend it and rallied people to the beaches with the slogan, “Just flip ’em” (if you see a crab helpless on its back, flip it over).

Now New Jersey totally prohibits fishing the limulus. Delaware’s limit is 100,000, males only. Maryland’s quota is 170,653, Virginia’s 152,495. This year, Ms. Zerbe happily announced “a major shift” – a horseshoe crab population increase due to the fishing moratoriums.
Indeed, the census counted almost 2 million.

Many people concerned with such things are satisfied with the management of the crab. Others argue that continuing to take half a million of them from the region’s waters every year is hardly good for the species, and for the animals that depend upon them. “The crab,” said Hall, “is a keystone species. Everything from minnows to sharks feed on its eggs; rockfish, flounder, turtles.”

But mostly birds do, tens of thousands of them, migratory species that visit this time of the year and those that live here permanently. There have been significant falloffs in recent years among species, like the ruddy turnstone, sanderling, and golden plover. Most dramatic is the population drop of the red knot, a small, red-breasted bird that winters in Tierra del Fuego and breeds in the Canadian Arctic. Between 1982 and 2006, its numbers fell from 140,000 to 40,000.

The bird strives to arrive in the Delaware Bay when the horseshoe crabs are planting their eggs on the beaches. It is a vital rendezvous. Without sufficient crab eggs to regain weight lost during its flight out of the south, the red knot can’t reach its breeding grounds in the far north.

Those opposed to the current policy believe a total prohibition against fishing the crab would slow these falloffs.

Larry Niles, of the Conserve Wildlife Foundation of New Jersey, wants a total moratorium because, he said, “Maryland and Virginia are taking crabs from the Delaware Bay by catching them before they migrate here to spawn.”

Whether an additional half million crabs in the sea would help the birds isn’t certain because, as Hall said, “Nobody really knows what’s causing this bird loss. It could be pollution, or something going wrong outside the area.”

Frank Eicherly, a former commercial bait fisherman who said he was squeezed out of business by current moratoriums, also thinks something else is killing the birds. He noted that over his long years as a waterman the birds sometimes failed to arrive when the crabs were spawning. If the limulus is late and fails to seed the sand with its eggs while the birds are there, the birds, though underweight, will depart northward, obedient to the imperative of their instincts.

That is what is happening this year. “So far the crab counts have been really low,” Hall reported last week, noting that storms in early May could have kept them from coming ashore. Meanwhile, most of the migratory birds have left. “I suspect this is going to be a bad year for the birds.” The limulus protects itself before all others. It knows the danger of landing in a rough sea. It has weathered all threats and defeated all obstacles through countless millennia.


To Stewart Michels, a biologist at Delaware’s Department of Natural Resources, the current situation offers a lesson in the evolutionary process: “The bird is specialized and perfectly adapted to things as they are. The crab is much more adjustable, a master of survival.”

The lesson: The perfectly adapted creature is the first to die when the situation changes.