Crustacean cannibalism found in bay Two studies examine blue crabs' dining habits

March 01, 1992|By Mark Di Vincenzo | Mark Di Vincenzo,Newport News Daily Press

NEWPORT NEWS, Va. -- Those who catch and study Chesapeake Bay blue crabs have long known that these grabby, mean-spirited shellfish do little more than look for food, fight for food and eat.

But there's new information about their dining habits: When there's not much food around, crabs eat a lot of crabs.

Two recent studies reveal they eat more of their own kind than ever imagined.

Scientists say it's a significant revelation because it proves cannibalism is an important factor that determines the blue crab population in the Chesapeake Bay.

The discovery disproves the long-held belief that crabs do not readily eat their own even though they are aggressive. Fishermen believed that because crabs stay away from pots baited with dead crabs. Scientists now theorize that crabs' bodies release a chemical that repels others.

But crabs eat live crabs.

A recent study by researchers at the Smithsonian Environmental Research Center in Edgewater shows young, small crabs are more likely than not to be eaten by older, larger crabs.

And a Virginia Institute of Marine Science researcher examined the gut content of more than 1,600 crabs caught in Virginia's York, James and Rappahannock rivers in 1988 and 1989 and found that 30 percent to 40 percent of the contents were crab remains.

"The results are really exciting, I think, because they are consistent over two years: I always found cannibalism," said Randa A. Mansour, a VIMS student who is writing a dissertation based on her findings.

Ms. Mansour's research found that crabs eat more crabs when clams, their favorite food, are less abundant, said VIMS crab scientist Romuald N. Lipcius, Ms. Mansour's mentor. Crabs cannibalize more often in the fall, after most clams have been harvested by fishermen or eaten by crabs, the research shows.

Although crabs have been seen digging worms out of mud and grabbing finfish, they prefer clams, especially soft-shell clams, because they can easily break their shells with their claws, Mr. Lipcius said.

But the gut-content research proves crabs don't dine solely on clams or oysters, another crab favorite.

"We now know they do readily cannibalize," Mr. Lipcius said. "The idea that cannibalism might be driving the system was not proven at all previously."

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