50,000 perch may have succumbed to disease and cold, officials say

Potomac fish kill probed

February 22, 2007|By Tom Pelton | Tom Pelton,sun reporter

SWAN POINT -- A combination of disease and last week's sudden cold snap might have caused the death of about 50,000 white perch in the Potomac River near this Southern Maryland community, state officials said.

Thousands of dead perch were heaped along the beach yesterday beside a wall of concrete boulders protecting an upscale subdivision. Scores of seagulls screamed overhead, and flies buzzed over the rotting fish.

"It's apocalyptic, seeing so much death all at once," said Mike Roller, field supervisor for an archaeological surveying company, who walked along the littered beach as he returned from a site his firm is examining for home construction.

Although a few striped bass were mixed into the pile, the fish were nearly all white perch, about 4 1/2 inches long, their eyes removed by the feasting gulls.

The Maryland Department of the Environment is sending samples of the dead fish to a lab to determine if they were infected with bacteria or parasites, said Charlie Poukish, environmental program manager for the state agency.

"They may have been weakened by some disease and were in the wrong place at the wrong time - with strong winds, cold weather and shallow water," Poukish said.

About three years ago, a bacteria called vibrio killed more than 100,000 perch in the upper Chesapeake Bay. Investigators are looking into whether that or other pathogens might have weakened the approximately 50,000 fish that piled up along a four-mile stretch of the icy Potomac River in Charles County, and another 2,000 that washed ashore near Tall Timbers in St. Mary's County, Poukish said.

The threat to human health is low because most fish diseases don't easily transfer to people, Poukish said. And the number of perch killed is not large enough to hurt the fishing industry.

The larger issue is whether a growing number of Chesapeake Bay fish are becoming sick because of pollution or changes to the environment, said Andrew Kane, an associate professor at the University of Maryland School of Medicine.

"There seems to be a trend over the last few decades of a large number of fish health problems and fish kills," said Kane, who studies fish health. "The question is whether there is change in the environment that makes these bugs more virulent or makes fish more susceptible."

For example, scientists have discovered that 50 percent to 80 percent of striped bass in the bay carry a disease called mycobacteriosis, Kane said. It rarely kills the fish, but its presence raises concerns about the health of the bay, Kane said.

Roller said he first saw the dead fish Feb. 15, after a storm that whipped the shore with fierce, bitterly cold winds and waves. The shallows of the Potomac were frozen, and the fish were trapped in the ice, Roller said.

The die-off was not reported until days later. Joe Martin, a volunteer member of an environmental group called Potomac Riverkeeper who lives on Swan Point, was strolling along the shore with his wife about 4 p.m. Monday.

"The beach was completely full of dead fish, all the way down," he said. "I've never seen so many birds or dead fish. ... It was really upsetting."

Martin called a hot line at the Maryland Department of the Environment on Tuesday morning, and the agency sent a team of investigators in a boat.

Bruce Michael, director of tidewater ecosystem assessment at the Maryland Department of Natural Resources, said the Potomac's health has generally been improving over the past 30 years. A series of upgrades to the Blue Plains waste treatment plant, which serves the Washington area, helped limit the huge algae blooms that used to cover the river in blue-green muck from shore to shore, Michael said.

A ban on phosphorus in detergent also helped, he said. Since then, the river has seen a resurgence of submerged aquatic vegetation, which has provided habitat for a good population of bass and other fish, he said.

But the river still faces serious problems. Every summer, algae return to the Potomac, sometimes spreading toxins that kill fish. Last summer, about 30,000 fish of a variety of species died off Cobb Island when they got caught in a fisherman's net and were killed by the river's low oxygen levels, caused by poor water quality. Charles County health officials twice last summer advised residents of Swan Point not to swim in the river because of high bacteria levels.

Leslie Martin, Joe Martin's wife, said they used to swim off their pier frequently a decade ago but rarely did so last year because of the bacteria.

"We have seen fish kills here before, but never as concentrated as this," she said.

Poukish, the MDE investigator, said there is no evidence of chemicals or other high levels of pollution that killed the perch off Swan Point. A power plant and two sewage treatment plants are nearby, but neither seems to have leaked.

Poukish and his colleagues were in a boat yesterday, collecting fish for lab analysis and testing the water's acidity and oxygen levels.

Howard King, director of the fisheries service at the Department of Natural Resources, said freezing weather alone does not usually hurt perch. "White perch are pretty hardy. They don't normally succumb to cold water temperature," King said.

It is not clear what might have harmed the fishes' health, possibly making them weak enough to be killed by being trapped in a shallow section of the river during the cold snap, Poukish said.

Vibrio and other pathogens are common in the bay and other bodies of water, often at harmless levels. "Vibrio is one of the common bacteria that we find with white perch," Poukish said. "But there could be other stressors involved," including other diseases or poor water quality, that may have weakened the fish, he said.

tom.pelton@baltsun.com

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