Chesapeake Bay Begins to Feel the Pinch of a Declining Crab Population : Environment: Teams of researchers use electronic telemetry to scrutinize crustaceans and their place in the fragile ecosystem.

EDGEWATER, Md. —  Sure, being steamed, squished into a cake, whipped into fluff or slathered with brown spice would be an ignominious fate. But for an undersize male crab, being thrown back into Chesapeake Bay these days may not be much better.

Watermen and diners aren’t the only ones who think biggest is best: Often, female crabs reject smaller males. And if a puny male finds a mate, that’s no picnic either. He has to haul the she-crab around and fight off predators.

Add to that the way development and pollution have wrecked a lot of favorite crab hangouts (grass beds, shallows, tidal creeks) and we’re talking about serious quality-of-life problems for Maryland’s official State Crustacean and, potentially, the people who love them.

“There’s a common belief that crabs are a tough, feisty, adaptable species that can take whatever you throw at them,” said Anson (Tuck) Hines, an ecologist at the Smithsonian Environmental Research Center in Anne Arundel County. “But they’re showing the same signs of overfishing that we saw in rockfish and other species.”

The possibility that even hardy, seemingly ubiquitous Callinectes sapidus may be feeling the effects of the Chesapeake Bay’s troubles is one of the unsettling conclusions of Hines and a dozen associates.

At their remote bayside lab here, just south of Annapolis, the researchers have developed ways to use electronic telemetry to scrutinize crabs’ most intimate behavior and try to understand their place in the fragile bay ecosystem.

An ultrasonic transmitter the size of a candy bar strapped to a crab’s shell and wired to various muscles allows researchers to not only track a crab’s location, but know when it chewing, mating, molting or menacing another crab.

Sitting in a boat and listening with a hydrophone and headphones, the researchers can count the transmitter’s beeps and know, for instance, precisely how many bites it takes a crab to devour a clam.

“We have a sense of urgency because I think we’re seeing all the danger signs,” said Hines, standing in the shade near the center’s dock on the Rhode River. In this peaceful spot at the mouth of the river, with fragrant orange trumpet flowers nearby and water skiers slicing the waves in the distance, the talk is of limb loss, cannibalism and environmental ruin.

Until recently, crabs caused little worry because their numbers, though fluctuating wildly, have shown no long-term decline. In the last few years, commercial crabbers in Maryland have been taking in a steady 45 million to 48 million pounds of crabs annually, according to the state Department of Natural Resources.

Amid the dwindling of oysters, striped bass and other species, the crab catch shored up the battered notion of the Chesapeake as a kind of aquatic horn of plenty.

But Hines notes that while the catch has stayed the same, crabbing has taken a big jump, with commercial licenses increasing from 2,700 in 1988 to 4,200 this year.

“This suggests to me that the crab population is tapped out, it’s reached its limit,” Hines said. “It’s reached the stage other fisheries did just before they went into decline.”

He and many environmentalists advocate a limit on the number of crabs caught--an idea that is sacrilege to watermen and political dynamite to state officials.

“We are really concentrating on other management techniques right now,” said Jim Casey, fisheries biologist with the Maryland Department of Natural Resources. “Promoting the release of little crabs, limiting the number of licenses, that sort of thing.”

While that debate simmers, the painstaking job of fueling it with new data continues on the Rhode. Graduate students and research fellows, working around the clock, go out in boats and listen to the clicking of the transmitter, carefully recording changes in its rate.

“The crab was tracked continuously for 96 hours while every contraction of the mandibular (jaw) muscle was recorded,” Hines and collaborator Thomas G. Wolcott, of North Carolina State University, wrote in a study. “The crab traveled 4,000 meters along the sub-estuary at an average speed of 12 meters per hour. The crab fed two to seven times per day, with a feeding bout comprising 15 to 2,750 bites.”

Such information is helping researchers to figure out, bite by bite, which elements of the crabs’ environment are essential to their prosperity and survival.

Hines, who has worked at the Smithsonian’s facility for 12 years, began looking first at crab movements and found through transmitters that large males go into salt creeks to molt.

A few transmitters wound up in unexpected places.

“One turned up at a Crisfield crab packinghouse. Unfortunately, it went through the steamers and was pretty much out of commission,” Hines said. “Another one was returned to us by a little girl who found it on a crab she caught off a dock.”

Lately, Hines has moved from these studies of freely roaming crabs to ones of crabs tethered to weighted lines, confined in wire enclosures in the river or placed in kiddie pools.

One finding--that crabs require many different habitats at various stages of life--comes as many of those habitats are being wiped out. Juveniles, for example, favored the submerged grasses ruined in the 1970s by excess nutrients and pollution.

Where are youngsters now? “They seem to be in the near-shore shallows--just the kind of shallows being eliminated by bulkheading,” Hines said. “People with expensive shoreline property want to protect it, but it’s cutting down on an important refuge for crabs.”

One reason young crabs need refuge is that it keeps them out of the hungry mandibles of their elders.

Hines contends that cannibalism is not adequately taken into account in state estimates of the crab population. “To decide how many crabs ought to be removed by man,” he said, “you ought to know how many are being removed naturally.”

One cannibalism study involves attaching a crab to one end of a piece of wire and a heavy nail to the other and just watching. “It’s sort of like staking a goat out there for a tiger,” Hines said.

Another phenomenon being studied is mating and its impediments--such as the crabbing industry’s predilection for large males, which bring top dollar in restaurants because many diners don’t like female crabs.

“On the retail level, we sell 10 times as many males,” said Doug Orr, manager of the Annapolis-based Maryland Waterman’s Cooperative. Orr said the average diner has “a psychological problem about encountering a sac of eggs” in the females.

“What’s the effect of this lack of the biggest guys to mate with the biggest gals?” Hines asked. “There’s a lot of competition. We’re looking at which males are losing out.”

Another hindrance to mating success may be temporary or permanent limb loss. Crabs have the ability, when a predator clamps down on a leg, to drop it off and escape.