Winter count of crabs tests the bay's health

ABOARD THE MYDRA ANN — ABOARD THE MYDRA ANN - The health of the Chesapeake Bay's struggling crab population is measured, not by the pounds of crustaceans caught each summer and fall, but by how many get scooped up in the middle of winter.

Dodging chunks of ice that have broken free from frozen rivers and docks nearby, a team of biologists and watermen spends weeks braving the bone-chilling winds of the bay to take hundreds of dredge samples.


With each scoop, they carefully pick through mud, oyster shells and assorted garbage to find blue crabs. They write down each crab's size, weight and gender for analysis, along with the salinity, depth and temperature of the water where it was found.

"We're doing 30 or 40 sites a day, so you really get rolling," says Roger Morris, a waterman based near Hoopers Island, hired by the state to provide a boat and crew for the survey. "This is kind of neat to see what's going on. ... They would tell us about how many crabs are out there, but I never knew before how they did it."


By the middle of February, the Maryland group and its companion team in Virginia will have surveyed 1,500 random sites along the bay.

"When you're looking for a reliable way to survey a population, there's nothing better than this," says Lynn Fegley, a biologist at the Maryland Department of Natural Resources. "These blue crabs are hunkered down in the winter and don't move, so you can sample them and get a real good idea of how many are there. There's almost no other survey like this in the bay because when you're talking about fish, they're always moving around."

After a bit of fine-tuning in the late 1980s, scientists developed a system that can now predict the size of the coming season's commercial crab harvest within about 6 percent.

Since 1990, their "Bay-wide Blue Crab Winter Dredge Survey" has emerged as a crucial and widely trusted measurement of the health of the Chesapeake Bay.

"We're extremely conscious of the fact that you can't judge the crab population based on harvest, because harvest has as much to do with the effort of the watermen as with abundance," says Ann P. Swanson, executive director of the Chesapeake Bay Commission, which published a major report on the crab population last year that relied heavily on the winter survey.

"These independent surveys are absolutely critical, and over the years the Chesapeake Bay Commission has repeatedly gone to bat for the funding to keep it going," Swanson says. "If we lose the continuity of that survey, we lose the depth of our understanding of the crab population, and it is those survey results that are driving the management and the regulations."

Over the past decade, the survey has shown a significant drop in the bay's crab population - a decline that has appeared to stabilize, and perhaps even slightly reverse itself, after three years of catch restrictions in Maryland and Virginia.

Nevertheless, officials believe the past year's catch by Maryland watermen might have been the lowest in 25 years, about 18 million pounds. But the lack of crabs was only one reason - the other was the strange weather of 2003. A cold spring and heavy rains (topped off by Tropical Storm Isabel) drove down the number of watermen trying to catch crabs and created difficult conditions for those working on the bay.


To start the annual survey, scientists from Maryland DNR and the Virginia Institute of Marine Science randomly select 1,500 sites throughout the bay, plus 125 that they check every year to provide continuity from one survey to the next. Maryland spends $40,000 for its share of the work.

Cold counting

Relying on the precision of a Global Positioning System, the Maryland crew has been going out almost every day since the middle of December, a two-month odyssey through freezing, gusty winds up and down the bay.

As the boat reached its position on a recent January afternoon in the eastern bay, just south of Kent Narrows, Bobby Patterson - also a Hoopers Island waterman - hopped on the flat platform on the rear of the boat, unhooked a scooping device known as a Virginia dredge, and tossed it overboard.

The dredge is 6 feet wide and covered by a nylon mesh liner with half-inch holes, and its edge sports 5-inch teeth.

A chain lowers the dredge to the bottom, as Morris - taking a position amidships at the engine controls - carefully pilots the boat at 3 knots, towing the dredge for exactly one minute.


The dredge's contents are then hauled aboard and dumped on the boat's stern platform to be sorted by Patterson and DNR fisheries biologist Glenn Davis.

In some areas, they'll find dozens of tiny crabs, little more than a few months old. Near Tangier Sound, they'll often find females. More than half the dredges produce absolutely nothing - largely because crabs tend to cluster when they burrow into the bottom, Davis says.

From time to time, the scientists will dredge the same spot repeatedly, essentially giving them a method to calculate how many crabs are actually located at a site after it has been dredged once.

On this first dredge in the eastern bay, as biologist Chris Walstrum checks out each specimen on the deck, the crew finds 17 jimmys - the crab equivalent of Boys Town.

"Male," Walstrum says, and then holds a crab up to a wooden ruler. "One-thirty-seven," he adds, meaning the crab is 137 centimeters across. He attaches the crab to a spring scale. "One-forty-eight," he says, reading its weight in grams.

Claws not a problem


With crabs all but shutting down their metabolism during the cold winter months, none snaps its claws, allowing Walstrum to work without protective gloves.

Fegley, meanwhile, uses a pencil to record the data in a mud-spattered notebook - pencil because ink smears in the spray, pens freeze up in the cold.

Once the vitals are recorded, scientists toss the crabs back in the bay. The animals, they say, quickly settle back into the muck, none the worse for their brief trip out of the water.

After a ride to the next spot, less than 10 minutes away, the dredge is released again. This time, scientists find nothing but pounds of oyster shell. The third and final site of the afternoon yields three more males and more empty shell.

In March, biologists will return to sample a handful of sites where they found crabs abundant the first time. "We want to know how many die during the winter, to get a better prediction of mortality," Fegley says.

Cold winters - particularly with low temperatures late in the season - can traumatize older, larger blue crabs, perhaps killing more than 10 percent. Scientists aren't sure why.


'Wait and see'

But ultimately, they'll have to answer the same question this year that they have in the past: How is the crab population doing?

A preliminary estimate based on the first half of the survey won't be released until next month, and Davis insists that it's too early to make an accurate prediction.

Still, he observes, "It looks comparable to last year. It's not deviating significantly. But we'll have to wait and see. We have a lot more to do."