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Volume 5, Number 4
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Blue Crabs
in Winter

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In the mid-1990s, many watermen reported that they were fishing harder and longer to catch fewer crabs, and some scientists warned that the stock could be nearing collapse.

By any account, this winter undertaking is impressive. Since 1989, following the pilot effort in 1988 at UMCES, both Maryland and Virginia have conducted a winter dredge survey. It's the only ongoing crab survey that samples sites throughout the whole Bay — 1,500 random sites and 125 fixed sites. Originally funded by the Chesapeake Bay Office of the National Oceanic and Atmospheric Administration (NOAA), the survey is now supported by the states of Maryland and Virginia.

When Morris arrives at the next station he drops the dredge a second time. Again the chain snaps tight and the Mydra Ann digs in. Will this random walk along the Bay bottom turn up any crabs this time? Looking south past Kent Island across the broad expanse of the Bay and down toward Virginia, one wonders — how could anyone ever expect to count all the crabs in the Chesapeake?

Where Do Crabs Come From?

If place of birth means anything, practically every crab in the Chesapeake is a Virginian. All the Bay's female crabs migrate south to the lower end of the estuary to spawn during the warmer months, from June to September. Though scientists believe females mate only once, they can have multiple broods, and their production is prolific — as many as 8 million eggs per spawn, when things are working right. After spawning, crab larvae drift to sea, where they grow in salty seawater. Beginning crab zoea sketch by Deborah Coffin Kennedyin about mid-July, the year's crop of tiny crabs starts returning to the Bay, a homecoming wave that continues right through October and into November. At the end of their month-and-a-half larval sojourn, they metamorphose from what looks like an extraterrestrial flea to something that resembles a cross between a shrimp and a crab (a megalopa). As the baby crabs return, they settle in underwater grass beds and other habitat in the lower Bay and continue to grow. By the time this crop of crabs reaches about three-quarters of an inch, about as big as a thumbnail, they begin to disperse into the Bay, though precisely what drives them — crowding or the search for food — remains unclear.

While Bay crabs are Virginians, many apparently move to Maryland for personal growth. Whatever the reason for their wanderings, by early autumn falling temperatures catch them and wherever they are crab megalop sketch by Deborah Coffin Kennedythey hunker down to hibernate.

Young crabs spend their first winter buried in the mud. In fact all Bay blue crabs, young or old, remain buried throughout the cold months, in a remarkable state of suspended animation. They don't move, don't feed. They barely breathe. As with all animals that hibernate, this capacity to wait, to slow down their physiology to just this side of death, allows them to make it through cold temperatures. Since they can't heat themselves metabolically, as warm-blooded creatures do, they have evolved a way to wait for warmer waters, when they can move again.

And move they do as Bay temperatures begin to rise above fifty-five degrees in the spring. A wave of crabs begins to emerge from the bottom, generally from south to north as the sun works its way back up from the equator. While some crabs are literally on a march up the Bay, scientists believe that many are simply emerging from their burrows as warmer temperatures gradually move up the estuary. This south-to-north warming may make it appear that crabs are moving north when in fact they are just popping out of the mud in sequence, from the lower Bay to the top — like sports fans rising in a wave.

With warmer waters, crabs go into high gear. They feed and molt and grow. Last year's crop of tiny crabs will now mature rapidly and mate during the summer. In less than a year, this batch of crabs will go from drifting larvae to mature adults, capable of mating. After they mate, female crabs will travel back down the Bay. Most overwinter and spawn early the next summer, though some precocious females spawn before water temperatures drop. Then the cycle begins again.

Tracking crabs during all this seasonal coming and going presents a real challenge. In addition to the winter dredge, scientists use a number of other surveys to keep up with blue crabs. Both the Maryland DNR and the Virginia Institute of Marine Science (VIMS) have run summer trawl surveys for many years, and George Abbe at the Morgan State Estuarine Research Center has run a crab pot survey since 1968.

These surveys, and especially the winter dredge survey, have proved crucial. In the past, resource managers relied largely on harvest reports to gauge the abundance of crabs in the Bay. Harvests are still an important barometer of blue crab stocks, but harvests respond to everything from weather to economics. When prices go down and costs go up, for example, crabbers may simply pull their pots.

Independent surveys paint a more accurate picture of the Bay's blue crab stocks by counting crabs the same way year after year, using statistically reliable methods. They also raise serious questions. Now that we can count crabs better than ever before, who will answer the question of how many crabs constitute a sustainable population? How many crabs are enough?

Conflict Over Crabs

There is arguably no one who has tried harder than Tom Miller to count the Bay's blue crabs. As a researcher, he is on the receiving end of all those data collected by Walstrum and Morris and the small army of others who labor at surveying the blue crab. A researcher at the UMCES Chesapeake Biological Laboratory, he works out of a small office in Kopp House, a quaint white cottage on the shores of the Patuxent River. Stacked with books and reports, his desk sports a crab sculpture that raises bronze claws toward the ceiling. On the wall a bumper sticker proclaims, Attack Crab on Duty. Deskbound this morning, Miller has to adjust the blinds to dim the bright winter light that bounces off the Patuxent just outside the door.

In the course of all his crab counting, the soft-spoken Miller has found himself smack in the middle of a noisy controversy. Disagreements over how blue crabs are doing — and whether recent declines reflect natural cycles or dangerous overfishing — have led to red-faced debates among watermen, researchers, environmentalists, and resource managers. And those debates have drawn the combatants to the types of studies that clutter his desk.

With a kind round face, spectacles, and close-cropped thinning hair, Miller looks at home here in his casual V-neck sweater, but it's been a long road to this perch on the Patuxent. Unlike Roger Morris or Chris Walstrum, Miller did not rise from the shores of Dorchester County or Kent Island. Born in Southeast London, Miller is the son of a London cab driver and, along with his sister, the first in their family to attend college. When he was about five his family moved downriver past Greenwich, and he still remembers playing by the marshes along the Thames. "It wasn't like this," he says, indicating the broad Patuxent just outside the window. "It was more like New Jersey."

Nevertheless, an interest in nature and in things marine stayed with him, and he is now a well-regarded expert. His expertise: the population dynamics of fish — and crabs.

When Miller came to the Chesapeake in 1994, he could not foresee the central role he would play in the great two-state debate over the blue crab. The question at the center of that debate: how much fishing pressure can the Bay's crab stocks withstand?

In the mid-1990s nervousness over the heavily fished blue crab had reached a fever pitch. Many watermen reported that they were fishing harder and longer to catch fewer crabs, and some scientists warned that the stock could be nearing collapse. Other watermen said crabs were fine, and some scientists stated that the stock decline was just part of a long-term cycle. Decision makers heard contradictory arguments from both scientists and watermen, as concern rose among seafood processors, environmental groups, and the general public.

While many watermen shared those worries about the crab, they also feared that new regulations could curb their catch. To address the controversy, the Chesapeake Bay Commission formed the Bi-State Blue Crab Advisory Committee (BBCAC), chaired by Delegate John Wood, Jr. from Maryland and Delegate Robert Bloxom from Virginia. BBCAC, as it came to be called, brought together legislators, scientists, watermen, seafood processors, and resource managers to seek consensus.

Health charts for the Chesapeake blue crab show that abundance (top graph) persists at below-average levels. Harvests (middle) have also fallen. The good news is that in 2005 fishing pressure (bottom schematic) fell below the target recommended by the Bi-State Blue Crab Advisory Committee in 2001. If fishing pressure stays down, stocks should rise, unless other environmental factors are at play. Graphs reprinted, with permission, from Blue Crab 2005 Status report, Bi-State Blue Crab Technical Advisory Committee, Chesapeake Bay Commission.

graph showing decline in total crab abunance 1990-2006
graph showing decline in hard crab harvest 1990-2006
graph showing decline in crab fishing pressure

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