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Fishing for the Cause of the Great Blue Crab Comeback

Bluecrab2 At Obrycki’s crab house in Baltimore, news of the Chesapeake Bay’s blue crab rebound inspired a round of drinks and a salute with wooden mallets.

 “I think it’s a positive sign that the Chesapeake’s cleaning up, and it’s good that we have it,” declared customer Doug Wren, as he and a group of friends slammed away at a pile of spice-slathered crustaceans.

Scientific surveys this winter estimated that crab populations in the Bay have more than doubled over the last two years, reaching highs not seen in more than a decade.  After years of decline, this year there were about 650 million crabs in the Bay, up from about 260 million in 2007.

But what was the cause of the crab comeback?  Was it really, as this diner suggested, a sign the Chesapeake is cleaner?

Dr. Anson “Tuck” Hines, director of the Smithsonian Environmental Research Center in southern Maryland, said the resurgence of crabs cannot be explained by any sudden decline in water pollution in the Bay.

“Why the population might have increased in the last couple of years is not entirely clear,” said Dr. Hines, a marine biologist. “But the single most important change that’s occurred during that time has been a change in fishery regulations."

Specifically, Virginia in 2008 banned dredging for female crabs as they hibernate in the winter in the southern Bay. And Maryland that year imposed strict new limits on the catching of female crabs.

To understand why these regulations appear to have worked so incredibly well, you have to know something about the crab’s lifecycle – and a strange phenomenon called the “march of the sooks.”

Doublercrab A “sook” is a mature female crab.  In the summer, females are preparing to shed their shells and mate.  So they spray a perfume of pheromones into the water to attracted interested males. The males, called “Jimmies,” raise their claws and perform courtship dances that involves spraying the females with their own pheromones.

If this chemical chit-chat goes poorly, the males may eat the females.  But if the dance goes swimmingly, the males lock the females in cradle positions, which keeps away other males and protect the females from predators. They remain doubled like this for several days as the females shed their shells and the pairs mate. 

After the new shells of the females harden, the Jimmies take off for the north, while the sooks head south on a long journey.

Millions of sooks join together in a vast underwater parade.  This army crawls and swims southward for hundreds of miles, over silt and sand, migrating toward the mouth of the Chesapeake Bay. The lower Bay is salty enough to allow the survival of crab larvae in the spring, after spawning.

But first, the sooks must get there.  And all along the parade route, thousands of traps, often baited with oily fish called menhaden, have been planted.  Many of the marchers are lured into these fast-food joints– and never come out.

“There is a very large fishery in the lower southern areas of Maryland that target these females as they are migrating to the lower Bay,” explained Dr. Eric Johnson, a fisheries ecologist at the Smithsonian.  “So essentially, you’ve got a large number of animals that are moving predictably en-masse.  It makes them a big target for a fishery, if you know predictably when and where animals are going to be.”

The female crabs that survive the trek to the southern Bay bury themselves in the mud to hibernate during the winter. But traditionally in Virginia during the winter, boats have dragged rake-like devices called dredges to scoop up the crabs.

Two years ago, Virginia put a temporary ban on this targeting of females. With the protections, more sooks were left to release millions of larvae in the spring, and Bay crab populations rose dramatically.

“The encouraging thing about this is that it shows that some species – particularly fast-growing, short-lived species, like the blue crabs – can respond very quickly to positive management changes,” Dr. Hines said.

To be sure, other factors – such as weather – could have helped the survival of more crabs. Water pollution remains an important factor in the survival of clams and worms that crabs eat, and the underwater grasses that young crabs require as shelter from predators.

But the most likely reason for the sudden jump in crabs over the last two years was the political courage shown by the governors of Maryland and Virginia when they imposed controversial limits on catching female crabs.

BLUECRAB It is important to note that, even with the recent rebound, crab populations today remain lower than they were as recently as the early 1990s. And two years of rising numbers does not make a trend.  The big risk now is that the success of the last two years will erode the political resolve needed to keep protecting female crabs until the species has fully recovered.

If Maryland and Virginia bow to political pressure and lift the regulations, we would be right back where we were two years ago, with an ugly end to the Chesapeake’s weird but wonderful underwater parade.

The march of the sooks should lead to the birth of the Bay's next generations, not terminate on a restaurant table.

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By Tom Pelton

Chesapeake Bay Foundation

(Photos by Yuri Huta, Chesapeake Bay Program and Joe Razes)



 

Comments

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All sooks should be off limits year round. No females should be taken from the bay in MD or VA.

That makes perfect sense to me, John. Most people prefer eating the male crabs, anyway. And in the long run, watermen will be able to catch more if there are more females left alone to produce eggs and larvae.

The catch is, something like 80 percent of all crabs caught in Virginia are female crabs (because the females migrate down to the southern Bay). So to say "stop catching all females" is to almost say to Virginia watermen, "stop catching crabs, period." The Virginia watermen would complain that's a solution biased unfairly toward the Maryland watermen, who are able to catch more males.

stop catching the females, no females means nothing for the bay for 10years. I want to see my sons catch crabs like I did when I was a child growing up on the bay.

Yeah, I love catching crabs with my daughters, too. We always throw back the females.

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