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Volume 16, Issue 46 - November 13 - November 19, 2008
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Voyages of Discovery by Lynn Teo Simarskiand Guy G. Guthridge

Counting Crabs off Calvert Cliffs

What 150,000 crabs taught scientist George Abbe

The tanned, wiry man working crab pots off Calvert Cliffs could be any ordinary waterman — except that he is putting his catch back over the side. Biologist George Abbe has been pulling pots here for 41 years, measuring, sexing and releasing each crab. He has accumulated a precious and unique long-term record of the blue crab population in Chesapeake Bay.

The scientist from Morgan State University Estuarine Research Center on the Patuxent River at Jefferson-Patterson Park has caught over 150,000 crabs since 1968. To put it in perspective, all those crabs could have fed a dozen people at over 4,000 crab feasts.

Today, he’s invited us along for the ride. As we pull out of Flag Harbor in a 20-foot Sea Hawk named Callinectes — after the blue crab’s scientific name — Abbe remarks that he is the only major surveyor to catch crabs “the way crabbers do it.” His T-shirt, depicting a basket overflowing with crabs, advises, Don’t worry, be crabby.

Abbe’s survey — the longest-running one using the same method and location — helps to assess the Bay’s blue crab stocks. Maryland and Virginia each do trawl surveys in summer, while a dredge survey samples random locations throughout the Bay in winter. Abbe monitors only one area: an eight-mile stretch from Governors Run to Rocky Point in Calvert County. But his data agree with larger surveys.

When the Chesapeake’s oyster and other fisheries plummeted, watermen turned to the blue crab, putting more harvest pressure on the population. In Maryland, crab landings surpassed the oyster in value in 1983. Abbe’s painstaking work over 30 years showed that legal-sized male crabs had dwindled to become a much smaller part of the population. The average male was also smaller. The crabs Abbe caught in the Patuxent River, where crabbing pressure is less, were bigger than those in the Bay. All of this led him to conclude that male crabs were being overfished.

His results helped convince regulators to increase the size of a legal crab by a quarter-inch in 2002. That may not sound like much, but it’s a fraction that can buy time for a big increase in growth. A crab grows in spurts with each molt. It will molt 26 times, sometimes even more, boosting its size by one-fourth to one-third with each molt.

Holding up a male, Abbe says, “Give this crab another six weeks to grow, and you’ll double the weight.”

Abbe picks a sponge crab out of a pot. Her shell apron has opened to accommodate an orange, rubbery egg mass that matches the scientist’s bright orange work gloves. A big female’s sponge can contain up to eight million eggs.

When this female was ready to mate, she had to do it in a once-in-a-lifetime, two-to-three hour window, Abbe explains. Yet almost 95 percent of females manage to mate. A male, detecting through chemical cues that the female was about to make her final molt into the soft-shell state, picked her up and carried her around to protect her. After mating, he continued to cradle her until her new shell hardened. Even though the female cannot mate again, she is able to store sperm and may spawn again if not caught.

Abbe checks pots at three sites, the middle one right next to Calvert Cliffs Nuclear Plant. He began the study, in fact, to sort out how the plant’s operations might affect the crab population. Over 14 years, he collected 75,078 crabs but didn’t find any effect from the plant. During that period, in November, 1981, he did make his record catch: 58 crabs in one pot. “Big ones, too,” he says. “We caught more than 15,000 crabs that year. That’s a lot of measuring.”

The Bay’s blue crabs are notorious for their fluctuating populations. “Each year is different. That’s why we’re out here,” Abbe says. “Crab abundances are very spiky. We don’t know why, but we can make some guesses.”

One idea is that because Bay larvae move to the ocean for early growth, conditions have to be just right to bring them back in. The return of many young could bring a bumper crop. Predators also play a key role in crab numbers.

Abbe hopes his work will contribute to a more sustainable fishery that will help keep watermen in business. “We don’t want to work it down to the point that there’s nothing left,” he says.

In 2007, Abbe caught 2,219 crabs, a disappointing haul. This autumn, with the season still underway, he passed 3,500. He is all for this year’s new crabbing regulations, which he expects will eventually improve the watermen’s harvests. Days spent like watermen give Abbe empathy for their plight. As a scientist, he says, “I might not catch anything, but I can still take home a paycheck.”

Abbe’s days as scientist and waterman end this year. After retirement, he’ll turn from crabs to waterfowl, with more time to carve exquisitely detailed decoys and birds like those that grace the entry to the Morgan State laboratory.

Meanwhile, he’s looking for scientists to take over a crab survey whose value grows by the year.

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