With lab success, scientists to release hatchery crabs

Some warn method won't fix bay harvests

March 21, 2002|By Heather Dewar | Heather Dewar,SUN STAFF

Encouraged by their preliminary success at raising blue crabs in the laboratory, a group of Maryland and Virginia scientists plans an experimental release of hatchery-raised crabs in Chesapeake Bay tributaries as early as this summer.

The scientists hope to find out whether rivers and creeks that don't seem to have many crabs can support them. If the test with about 40,000 young crabs works, it could be a first step toward trying to supplement the bay's hard-pressed crab population through captive breeding.

Such an effort, if it happens, is years away, the scientists say. And watermen, fishery managers and bay conservationists are skeptical. They stress that hatchery crabs are not the cure-all for the troubled blue crab fishery, which has seen record- low harvests for the past two years.

"I think it's important that people understand what we expect to get out of the work ... is learning more about crabs," said Eric Schwaab, fisheries director of the Maryland Department of Natural Resources. "I don't think there's anybody who believes at this point that we could somehow use hatchery crabs in a way that would meaningfully enhance the Chesapeake Bay stock."

The blue crab population can't be restored unless the bay states also protect their habitat, reduce pollution and limit the number of crabs that are caught, said Larry Simns, president of the Maryland Watermen's Association.

"This is not a short-term fix," Simns said. "You can't substitute for nature. ... We don't think you'll ever be able to hatch so many crabs that you won't have to have regulations."

But Yonathan Zohar, who directs the marine research institute, which runs the hatchery, is not so quick to dismiss the idea that hatchery crabs could someday help restore blue crabs.

"We're just starting to explore a new avenue," said Zohar, director of the University of Maryland Biotechnology Institute's Baltimore lab. "I can't say whether this is going to be commercially successful or not, but I think this is a tool we cannot afford to ignore."

Scientists say the species is being fished to the maximum and may be overfished.

Blue crab harvests have fallen from 55 million pounds in 1993 to a low of 20.2 million pounds in 2000. The 2001 catch improved slightly, to 20.5 million pounds - the second smallest on record.

Maryland and Virginia officials are imposing new restrictions on crabbers in an attempt to enable a higher percentage of crabs to survive and repopulate the bay.

At a scientific conference held at the institute's Inner Harbor laboratory this week, Zohar said the hatchery work is shedding light on crabs' life cycle - which may prove useful in any restoration effort.

The researchers discovered that lengthening spring and summer days are the signal that prompts crabs to become fertile and mate. By exposing captive crabs to long days of artificial light that mimic spring and summer conditions, the scientists have triggered year-round mating and hatching.

The scientists have successfully raised crabs from eggs to adulthood. The process takes about eight months in the lab, though experts think that in the wild, most crabs take two years to mature.

The researchers hatched about 6.4 million crab larvae. A little more than 1 percent lived to adulthood, Zohar said. A major problem in the hatchery, as in the wild, is cannibalism, with the youngest hatchlings being eaten by older ones.

Biologist Rom Lipcius of the Virginia Institute of Marine Science would like to use hatchery crabs to test a theory that some of the bay's rivers and creeks could support more crabs than they do.

In experiments on the York River, Lipcius found that young crabs rely on tides to carry them upstream into rivers and creeks, and they aren't spread out evenly. Another experiment found that although the crabs were most abundant in the underwater grass beds that are considered their prime nursery areas, a greater percentage of them survive to adulthood in muddy or sandy areas upstream, he said.

"That's been a real surprise," Lipcius said. The crabs may be thriving in muddy areas because they have fewer predators and more of the clams that are their favorite food, he said.

Lipcius said he wants to plant hatchery crabs in grassy areas and others on muddy bottoms and see where they end up. The results could show whether some areas that produce very few crabs now might yield more with hatchery-raised animals, he said.

Lipcius said he intends to conduct the experiments this summer if the hatchery can produce enough baby crabs. If not, he'll do a trial run with crabs caught elsewhere in the bay and moved to the experimental areas, he said.

The proposed experiment would need approval from fishery managers in Virginia and Maryland.

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