Volume XI, Issue 28 ~ July 10-16, 2003

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Burton on the Bay | Chesapeake Outdoors | Sky Watch | Tidelog
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Chesapeake Outdoors by C. D. Dollar Horseshoe Crabs at Work and Play

Perhaps I should have felt uncomfortable invading their privacy, but they were going at it in plain view on the beach. Oblivious to the stares of curious onlookers, these primordial relics went about their intimate dance as they have for tens of millions of years.

The crabs scramble from the Bay, timing their exits with the spring tides. As they negotiate crashing waves to fulfill their instinctual obligations, they resemble Abrams tanks more than amorous conspirators. It’s a wonder they get the job done at all.

But they are indeed a marvel of nature. Amazingly, the external appearance of the horseshoe crab hasn’t changed in 360 million years.

Wiggling and writhing in the sand like poorly functioning robots, the smaller males use their specialized pinchers to latch onto the females’ carapace during copulation. An individual female can lay nearly 90,000 eggs, which are deposited in clusters or nest sites along the beach, near tide marks.

After a month or so, the eggs develop into larvae that swim around for a week before settling to the bottom. Here, they molt, then move onto mud flats for the next two summers.

Horseshoe crabs are most common in mid-Atlantic waters, but their range extends from the Yucatan Peninsula to northern Maine. Scientists theorize that each major estuary has a distinct population that can be distinguished from another by size of individuals, shell color and eye pigmentation.

The Bay’s horseshoe crabs are year-round residents, and in late May they move onto sandy beaches to mate and lay eggs. This year, however, the spawn was nearly six weeks late, presumably a result of the cold, wet spring.

These bottom-dwellers are not true crabs. Lacking antennae and mandibles, they’re more closely related to spiders and scorpions. Horseshoe crabs fill a key ecological niche as food for juvenile loggerhead turtles as well as for several shorebird species, which fuel up on the eggs on their return flight to Canadian breeding grounds. Researchers estimate that migratory shorebirds eat nearly 320 tons of eggs each year.

At one time, the main use of horseshoe crabs was as poultry and livestock feed and as fertilizers. Now they are used as bait for eel, conch and catfish. Egg-laden female horseshoe crabs are preferred.

The horseshoe crab fishery has never been well studied, but estimates for the commercial harvest along the northeastern Atlantic coast for the last 30 years range between 10,000 and two million pounds. Since 1988, commercial landings have averaged 950,000 pounds. But the accuracy of the harvest numbers is debatable since sales between harvester and fishermen are often a cash deal between individuals.

Medical science has also benefited from this natural marvel. Crabs are used for surgical sutures and for detecting bacteria. The discovery of limulus amoebocyte lysate (LAL), a clotting agent in the creatures’ blood, helps detect spinal meningitis and other pathogens in human blood. Drug producers get LAL by annually bleeding about 200,000 large horseshoe crabs, which must be released back into the wild. Not all survive, of course.

And to think at one time I thought they were just out for a little summer beach fun.

Fish Are Biting
Recreational crabbing seemed to pick up last week, perhaps because more people were out trying to get a holiday meal.

Rockfish remain strong, and bluefish are reported off Drum Point and Point No Point.



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Last updated July 10, 2003 @ 1:13am