New signs of ills in bay Sores on rockfish, decline in zooplankton, menhaden cause worry

Scientists are puzzled

July 12, 1998|By Heather Dewar | Heather Dewar,SUN STAFF

Disturbing new signs of trouble are cropping up among some of the most important creatures in the Chesapeake Bay's web of life: the rockfish that fishermen love, the menhaden that feed rockfish and dozens of other bay denizens, and the tiny aquatic animals at the base of the food chain.

In an unusual brainstorming session last week, 60 scientists from as far away as South Carolina tried to figure out why the bay's menhaden are in decline, while its rockfish are suffering from a persistent plague of sores that are different from last summer's Pfiesteria outbreaks.

The scientists agreed only that it's too soon to tell whether the changes are entirely natural, or whether they are warning signs of still-unknown environmental woes.

Some of the changes that have them worried are so subtle they can only be seen with a microscope:

Bay zooplankton, animals no bigger than a newborn baby's fingernail, have dropped sharply in abundance since 1984, according to data collected by the Chesapeake Bay Program.

These homely shrimplike, crablike or spiderlike creatures are a crucial, nearly-invisible link in the bay's food chain. Normally, they're abundant in nearly all watery places, eating algae and being eaten in turn by newly hatched fish, such as menhaden. Zooplankton declines of as much as 75 percent in the middle and lower bay are "a mystery," says biologist Claire Buchanan of the Interstate Commission on the Potomac Basin, "but the real question is how it trickles up the food chain."

There has been a regionwide decline in the numbers of young menhaden, a bait fish so abundant it is counted in billions.

Spawned at sea and swept into the bay by ocean currents, the silvery fish are food for virtually everything bigger than they are: rockfish and bluefish, sea trout and white perch, ospreys and herons and even blue crabs. Nine years ago, scientists estimated there were about 5 1/2 billion 1-year-old menhaden in Atlantic coastal waters; now the figure is down to 1.4 billion. Again, no one knows why.

Finally, there are the rockfish sores -- caused not by Pfiesteria but by common bacteria that rarely bother a healthy, wild striped bass.

One in 10 had sores

Last summer, researchers in Maryland and Virginia found about one in 10 rockfish were afflicted with these sores, ranging from rashes sprinkled like red sand across their backs to deep wounds resembling the slash of a knife.

Many were so emaciated it was a marvel they hadn't died of starvation, while others' kidneys or hearts were so badly damaged that "how the fish were alive at that point, I don't know," says senior scientist Eric May of the Maryland Department of Natural Resources.

The Solomons Island summit was inspired in part by Jim Price, a former Oxford charter boat fisherman turned environmental gadfly. For months, he's been pestering people to listen to his warnings about sickened, starving rockfish.

Price and some other bay watchers think the newly documented problems fit together as neatly as a set of nesting dolls: fewer zooplankton mean fewer menhaden; fewer menhaden mean that bigger fish are going hungry; starving fish are weakened and easily fall prey to diseases they'd normally shrug off.

It's a tempting theory, but after two days, the scientists remained unconvinced. After two days of discussion, the experts could only agree that all three sets of changes are real, puzzling and potentially important for the health of the bay.

"We could develop an incredible number of alternative hypotheses," says Wolfgang Vogelbein, a Virginia Institute of Marine Sciences expert on fish diseases. "I would just caution us as a group not to jump on any one of them.

"There's something going on, that's for sure but the environmental factors are an open book."

The zooplankton declines, for example, could be caused by natural variations in rainfall and temperature, Buchanan says.

Or it could be that the tiny animals are being out-competed by certain kinds of algae that thrive in polluted waters like those of the bay.

Natural forces could also be behind the shortage of young menhaden, says John Merriner of the National Marine Fisheries Service's research lab in Beaufort, S.C. Storms or currents could sweep newly hatched larvae out to sea instead of into the bay.

The menhaden decline is worrisome because menhaden are a staple in the diet of so many bay creatures. Some experts say rockfish, for example, rely on the small fish for half of their food supply.

Very little in stomachs

Price is running his own unscientific experiment, catching rockfish and slitting open their stomachs to see what they're eating. In better years, he said, the big predators' bellies would be stuffed with menhaden. But more than two-thirds of the 47 fish he's examined recently "had very little food in their stomachs and very little body fat," he said.

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