Bay's oyster revival threatened in drought

Increased risk of disease for bivalves

but crabs thrive in salty rivers

August 08, 1999|By Tom Horton | Tom Horton,SUN STAFF

The weather that is ruining farmers' harvests across Maryland is also threatening one of the greatest oyster crops to befall Chesapeake Bay in years.

"It was an amazing gift. We're just holding our breath now," said Chris Judy, director of the Department of Natural Resources Shellfish Division.

Judy was referring to the unexpectedly bountiful "spat set" or spawn produced by the bay's decimated oyster population back in the summer of 1997.

Those spat have been "growing like wild," Judy said, and are rapidly nearing the marketable size of 3 inches in length.

Equally important, he said, is the job the oysters are doing of filtering and cleansing bay waters and providing habitat for other aquatic life.

The drought, by reducing fresh water in rivers that flow into the bay, has allowed ocean water to penetrate farther up the estuary, pushing up salinities to levels that favor oyster diseases such as dermo and MSX.

Judy says the water is now salty enough to spread and increase the intensity of both diseases, which arealways present in the bay.

It will be October, when biologists begin annual sampling of oyster bars, before any good assessment of damage can be made, he said.

The great "spat fall" of 1997 did not occur everywhere. But in Eastern Bay near Kent Island, in significant portions of the Choptank and Little Choptank rivers, and the St. Mary's River in Southern Maryland, "It is a beautiful sight, billions of oyster growing down there," Judy said.

He and other bay managers say more is at stake than the oysters' contribution to water quality and the seafood economy.

In the past few years, political and financial support has been building toward a major attempt at restoring the bay's oyster population, estimated to be as low as 1 percent of historic levels.

The serendipitous oyster explosion of two summers ago was a significant factor in rekindling enthusiasm for restoration, and to lose it would be a blow.

A massive oyster die-off alone would be enough to declare the drought a loser for the Chesapeake.

But overall, the drought's effects on the bay are mixed. By its nature the estuary is a combination of salt and fresh water, and of species adapted to one or the other, or to both. And as reduced river inflow allows ocean salt to rule, there will be winners and losers, bay managers say.

Saltier water is actually good for oyster reproduction. Yet it also produces the profusion of stinging sea nettles, which in turn eat lots of tenophores, a jellyfish that consumes bay anchovies, the biggest food source for the bay's larger fish. With tenophores down, scientists expect a banner year for the critically important anchovy.

The drought also produces interesting visitors. "We are seeing jack crevalle [an ocean species] being caught in fishermen's nets on the Potomac," said Harley Speir, a fisheries biologist with the Department of Natural Resources.

Blue crabs are also surging farther than usual up the rivers. "They are catching them just below Denton on the Choptank, and I haven't seen that since the 1980s," he said.

Just how much the drought has reduced freshwater inflows could be seen last week on a measuring gauge in the Choptank's headwaters, at Greensboro, several miles above Denton. The flow there was an astounding 50 times less than normal for August.

In theory, water quality in the bay should benefit from the drought, because fewer pollutants will be washed from the land and flushed out in ground water, scientists say.

The levels of oxygen in the bay -- an indicator of aquatic health -- appear to be slightly higher this summer, said officials of the U.S. Environmental Protection Agency's Chesapeake Bay Program. Growth of aquatic grasses also appears to be better.

However, there have been blooms of oxygen-robbing algae in bay tributaries, causing large fish kills in the Pocomoke, Magothy and Patapsco rivers. The drought is probably a factor but not necessarily the only one, said Speir.

He said drought, pushing salt up the bay's rivers, can "compress the normal zones" of fresher water that are optimal habitat for fish such as yellow perch, crappie and largemouth bass.

If the drought's effects persist into the spring, he said, it could also "squeeze" areas where rockfish enjoy the best spawning success. Preliminary evidence for this summer is that rockfish spawning has been moderately successful.

Concern for fish habitat is also growing on the Susquehanna, which provides as much fresh water as the estuary's 40-odd other tributaries combined.

The Susquehanna is running so low that as Baltimore begins pumping drinking water from it to augment its shrinking reservoirs, flows of water passing through Conowingo Dam near the river's mouth may have to be held back, said Susan Obleski, a spokeswoman for the Susquehanna River Basin Commission.

The reason is that several big water users, including a nuclear power plant, have water intakes in the top 8 feet of water pooled behind Conowingo, she said.

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