'No anchovies please' not in bay order

ON THE BAY

April 08, 1995|By TOM HORTON

Some memorable fishing experiences on the Chesapeake Bay, which now need revising:

* Hooking huge weakfish on a hot summer night, until my wrists ached, on the edge of the main ship channel in midbay. They hit the deck, bellies bulging, literally coughing up quantities of a tiny bait fish that seemed unimportant in the flush of the moment.

* A frigid winter day -- and night, and another day -- fishing with gill nets nonstop amid ice floes with the bay's biggest rockfish netter, piling up stripers by the ton. They too hit the deck spitting up a tiny bait fish on which they had been gorging in the icy depths of the upper Chesapeake.

* Watching 30-ton humpback whales roll as they fed this spring in the ocean at the bay's mouth. Scientists using trawl nets near the whales said the nets came up almost solid with masses of a tiny bait fish, which seems to be what is drawing more and more humpbacks.

For most of the bay's top predators -- from rockfish to weakfish, flounder, bluefish and humpback whales -- one tiny bait fish underwrites them all. It seldom grows to more than a few inches, lives only about a year, and hundreds of them together weigh barely a pound. But at the peak of its yearly population cycle, there may be as many as 50 billion of the little fish out there, populating virtually every nook and cranny of the bay.

Its proper name is Anchoa mitchellii, the bay anchovy, and it may be the single most important fish in the Chesapeake Bay.

"Bay anchovies are the keystone species," says Bob Ulanowicz, a University of Maryland bay scientist who specializes in charting how energy flows through the Chesapeake ecosystem. He explains that the anchovy links the highly visible components -- rockfish and bluefish, for example -- to the plankton that suffuse bay waters like the near-invisible dust motes you see when a shaft of sun illuminates the air in a room.

Think of the process as a wave, one that begins building each spring, as snow melt and rainfall engorge tributary rivers, flushing the winter-weary estuary with nutrients and minerals jTC washed from 40 million acres of land. By May, this has stoked a mammoth production of tiny plants and animals (phytoplankton and zooplankton) in the estuary.

Then the bay anchovies feed ravenously on the zooplankton, gearing up for a spawning binge rivaled by few other creatures. Every day, for up to 50 days, the little anchovies release a thousand or more eggs -- totaling three times their own body weight by summer's end.

By comparison, a female striped bass, considered an impressive spawner, produces 200 eggs per gram of body weight each year; a female anchovy manages an astounding 30,000 eggs per gram.

By July, it is difficult to trawl a fine-mesh net anywhere in the bay without fetching up eggs and larvae of the bay anchovy.

By November, the food energy of the spring runoff has been translated, through the plankton and the anchovys' spawning, into peak populations of tens of billions of anchovies.

And this sets a banquet table at just the time when the bay's larger fishes, as well as hosts of sea birds -- loons and gannets, gulls and terns -- are slurping bait to build their own energy stores for the winter and to fuel their own migrations and reproduction.

Scientists have estimated that for some of these feeders, bay anchovies supply from 60 to 90 percent of total energy intake during most of the year. To be sure, the anchovy is not alone as an important forage fish in the Chesapeake. Silversides, another minnow, are super abundant at times, as are gobies.

And the humble menhaden, fished commercially in the Virginia bay for oil and fertilizer, appears in staggering quantities; from 200 million to 300 million pounds of menhaden have been harvested annually from the bay in recent times.

Menhaden, which feed by filtering phytoplankton from the water, are so plentiful that they may remove significant quantities of the excessive algal growth that is a target of bay cleanup efforts, scientists say.

No one can gauge with any precision the relative impacts on the Chesapeake Bay and its food web from menhaden, silversides, gobies and others. But none appears to equal the bay anchovy in year-round accessibility and widespread distribution.

Silversides, for example, are creatures mostly of the shallows; menhaden leave the bay in winter and grow too large after a time to be easy snacks for some predators.

Because the anchovy is so fundamental to the workings of the whole bay, several questions about it intrigue researchers, says Ed Houde, a fisheries ecologist with the University of Maryland and an authority on the tiny fish.

For example, there are good indications that the stock of anchovies in the bay can vary hugely from year to year.

How and why this variability occurs, and how it affects the species that depend for food on the anchovy, all need to be better understood by those who would manage the bay's resources, Houde says.

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