By Peter S. Goodman
Washington Post Staff Writer
Thursday, January 1, 1998; Page D01

New data show that the number of young anchovies and menhaden, vital food for larger fish, has declined to historically low levels in the Chesapeake Bay, heightening concerns among environmentalists about the future health of the bay.

Environmentalists are citing the data, compiled recently by the Maryland Department of Natural Resources, as evidence that the bay is threatened by aggressive commercial fishing. They are calling for greater conservation efforts to allow depleted species to rebound.

"This really hits home with the need to have broader-based fisheries management," said Bill Goldsborough, chief scientist at the Chesapeake Bay Foundation, an environmental advocacy group. "What we have now is a food web that's out of balance."

But other scientists and state officials played down the significance of the new data, which they called sketchy and inconclusive. The data show that anchovies and menhaden now amount to 1 percent of their historic highs.

No one is sure what has caused the decline in the young of the two species -- a source of food for bigger fish such as striped bass, bluefish and weakfish -- but some said they think the dip may be a negative side-effect of a striking success story: the return of the once-threatened striped bass, better known around the Chesapeake as the rockfish.

In 1985, Maryland imposed a moratorium on catching rockfish after stocks were fished and polluted to the brink of extinction. The state lifted the ban five years later. Since then, the state has seen rockfish spawning in record numbers.

Now, some speculate that all those rockfish are putting the squeeze on the menhaden and anchovies that feed them. With such a possibility in mind, environmentalists and fisheries scientists are reaffirming calls for fishing quotas to take into account not just single species, but all species, acknowledging the links among them.

"We need to manage the resources collectively," said Donald Boesch, president of the University of Maryland's Center for Environmental Science.

State officials said the recent dips in the two species may simply reflect a truism about nature: Fluctuation is the norm.

"You can never have all the populations superabundant at all times," said Pete Jensen, deputy director of the fisheries service at the Department of Natural Resources. "It just can't exist in nature."

Moreover, data collected after the state study by the University of Maryland's Chesapeake Biological Laboratory found greater numbers of young anchovies, said fisheries scientist Edward D. Houde, suggesting that the species may already be on the rebound.

"We see the numbers going up and down wildly from year to year," he said. "That's what we're accustomed to seeing."

Virginia officials have seen no dramatic declines in the two species.

Menhaden and anchovies are of great value to countless other living creatures in the Chesapeake, serving as a highly important source of food. They form the link in the food chain between plankton and bigger fish such a striped bass.

Although Chesapeake anchovies are not caught commercially -- the ones on your pizza typically come from deeper seas -- they are the most abundant fish in the bay. Menhaden are scooped up by watermen in pound nets and purse seiners up and down the east coast. Rendering plants turn them into fish meal and fish oil, which wind up feeding a variety of land-dwelling animals.

Remove the fish from the food chain, and you would expect to see declines eventually in the size and number of fish that feed on them. Indeed, the declines in the two species were discovered as part of a state study of rockfish conducted last summer to try to understand why more rockfish seem to be afflicted by sores and why many are undersized.

Goldsborough theorized the return of the rockfish may have triggered a downward spiral. First, more fish cut into the numbers of menhaden and anchovies, reducing the stocks. Then, with less to eat, the rockfish began showing signs of poor nutrition.

The National Marine Fisheries Service, which tracks menhaden populations, has seen declines in the number of young menhaden in recent years, for reasons unknown, said Douglas Vaughan, leader of the population dynamics team at the fisheries service lab in Beaufort, N. C.

At the same time, Vaughan said, the total population of menhaden -- which reach the billions, extending from northern Florida to Canada -- appears to be near the top of its historic range, suggesting that any dip in the Chesapeake is a local phenomenon.