Rockfish spawn confounds biologists Excellent conditions fail to deliver expected population

August 14, 1991|By Liz Bowie | Liz Bowie,Sun Staff Correspondent

TOLCHESTER BEACH -- After a year of boom and a year of bust, striped bass reproduction is running slightly below average this year, according to preliminary estimates by state fisheries biologists.

"It doesn't look like a disaster, but it is not what we hoped for," said Donald T. Cosden, a biologist with the Department of Natural Resources, as his eagle eyes picked out a young striped bass among a net full of silver sides, perch, anchovies and other species during a day's search on the bay.

"The good news is that we are on the rebound. The bad news is we are still below the long-term average."

Average is relative, however. In only two of the past 10 years has the species been able to muster a better-than-average reproductive year. The 1980s were filled with years of steep drops in reproduction that spurred most East Coast states to ban striped-bass fishing.

Each summer for the past 30 in Maryland, biologists have swept the Chesapeake Bay's shallows with nets

searching for evidence of the reproductive success of the striped bass.

They spend six weeks getting to 22 locations on the bay, pulling seine nets at each site twice, counting thousands of fish and collecting hundreds of specimens.

It is a lot of hoopla for one fish species.

But the striped bass, sometimes called rockfish, has come to symbolize the bay's decline and its restoration.

And the results of this annual rite of summer are hot news for another species -- the Atlantic coast sports fisherman, found between Albermarle Sound in North Carolina and the coast of Maine.

The striped bass is closely watched each spring as it enters the Chesapeake and heads back up its natal waters to spawn. What happens in the nursery grounds of the bay will to a large degree determine the health of the entire species.

This year, the biologists found a large brood stock, the term they use to describe the female striped bass that are round and ripe and ready to deposit their eggs at the edge of the tidal regions of rivers.

This year's weather was perfect for the spawn, said Richard K. Schaefer, assistant leader for the striped bass project at DNR, who spent days watching the oily slick of eggs float along the surface of the water on spawning grounds.

This spring there was a gradual increase in temperature and no sudden rainstorms that would cause the water temperature to dip suddenly and kill the baby fish.

So the state biologists were hoping for another bumper crop like 1989's, when the nets they walk the shoreline with were sometimes jumping with more than five or 10 young striped bass.

That year the first effects of the fishing ban resulted in a record number of brood stock and a record spawn.

The index of juvenile fish was an average 25 fish per haul of the seine net. Based on those results alone, states along the East Coast partially lifted the ban.

Last year, the cycle went bust again. The index plummeted to 2.1, the lowest since 1983.

This year, with the conditions so good but the spawn disappointing, fisheries biologists are shaking their heads in puzzlement.

Biologists believe the young fish are being killed off. But they don't know what is doing it. The answer could be as simple as Mother Nature, or as complicated as the effects of a mixture of several man-made pollutants, including acid rain.

And another scientific puzzle has popped up.

While Mr. Schaefer and Mr. Cosden buzz around the bay in a boat looking for rockfish in the locations they have surveyed for years, other fisheries biologists were finding large numbers of baby rockfish in places they wouldn't have expected -- the Severn River near Annapolis and the Miles River near St. Michaels.

In one haul of a seine net, a team surveying for other species found some 80 rockfish. The numbers could have been a fluke. But they are surprising.

"It is showing us that there are a reasonable number of fish in these other [river] systems" that have not had young striped bass for years, Mr. Cosden said.

Maryland's commercial and recreational fishermen will be able to catch rockfish for a short season again this year. But next year, if the juvenile index is poor, the department may be forced to reconsider whether to impose more stringent controls on fishing in 1992.

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