Rockfish success story takes an unexpected turn

Main food declining

more disease noted

June 24, 2000|By Joel McCord | Joel McCord,SUN STAFF

The Chesapeake Bay's rockfish population, once threatened with extinction, has rebounded to the point that scientists wonder whether the estuary's complex ecosystem can support it.

There are more rockfish in the bay now than in the last 30 years, according to the state Department of Natural Resources. But menhaden, the favorite food of rockfish, are declining rapidly.

Watermen say they've been catching diseased, underweight rockfish, and a University of Maryland study suggests that a significant portion of the bay's premier fin-fish is being infected by a common bacterium that would not affect them if they had enough to eat.

More than half of 300 rockfish in that study had signs they had been infected by the bacteria, which sometimes cause sores and can be passed on to humans as "fish handler's syndrome."

Anthony S. Overton, who conducted much of the research, says he is unsure of the significance of the rate of disease because "we have nothing to compare it to."

But Wolfgang Vogelbein, who is conducting similar research at the Virginia Institute of Marine Science, says his results support Overton's.

"It's a density-dependent phenomenon," says Bill Goldsborough, senior scientist at the Chesapeake Bay Foundation. "They're crowding each other out, they're not getting enough to eat, their resistance is down, they're starting to get sick, and because there are so many of them, the disease spreads."

DNR spokesman John Surrick says there is no evidence of rockfish dying in large numbers, but the department is "concerned" because the results of the study mean "there's something out of balance in the system."

John Wolflin, the U.S. Fish and Wildlife Service's Chesapeake Bay supervisor, says the bacterium, called mycobacteria, is insidious and wouldn't be noticed so soon.

"You won't see a mass fish kill," he says. "But a lot of fish are sick out there. They're not going to die right away, but they're going to die over time."

The Atlantic States Marine Fisheries Commission placed a moratorium on the catch, sale and possession of striped bass on the East Coast in 1985 after a decade of declining commercial landings. The commission lifted the moratorium 10 years later after the species made a stunning comeback.

But two years ago, scientists began noticing disturbing signs of trouble in the bay's web of life. Zooplankton, animals smaller than the tip of a pencil that are at the base of the food chain, were declining, as were menhaden, which feed rockfish and dozens of other bay denizens. At the same time, rockfish were suffering from sores ranging from rashes that speckled their backs with red to deep wounds resembling the slash of a knife.

The DNR commissioned several studies to figure out what was going on, among them the one that was released this week by the Cooperative Fish and Wildlife Research Unit at the University of Maryland Eastern Shore in Princess Anne. The study concluded that rockfish are eating more juvenile crabs and bay anchovies with the decline of menhaden and that there is a "strong correlation" between the change in diet and the apparent increase in disease.

Jim Price, a former Cambridge waterman, charter boat captain and environmental activist, insists that the lack of menhaden is leading to death and disease among rockfish. "These fish are so skinny, there's not enough to eat," he says. "I cut them open and there's nothing in their stomachs."

But Steve Jordan, head of DNR's Oxford lab who is finishing another rockfish study, says the relationship between the lack of menhaden and malnutrition and disease in rockfish is not so certain. Studies from 1992, 1993 and 1998 show some decrease in the size of menhaden, but "that's too small a period of time to call it a trend," he says.

"We're probably looking at a population under stress from the lack of forage and overpopulation," he says.

Eric Schwaab, DNR director of fisheries, says the overall rockfish population appears to be in good shape, despite the diet changes.

"Our biologists were doing tag surveys the first two weeks in June. They were looking at thousands of fish, and they say these fish are looking great."

Yet he acknowledged he is worried about the lack of menhaden.

Maryland has lobbied the Atlantic States Marine Fisheries Commission, which regulates East Coast commercial fishing, to set aside a portion of the menhaden stock to feed larger bay fish.

The commission is reviewing options for managing the menhaden fishery, which is concentrated in Virginia's portion of the bay and off coastal North Carolina.

"We need to leave more menhaden out of the fishery and in the bay as a food source," Schwaab says.

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