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Great Lakes Article:

Lake Erie Fish Kill Under Investigation

07/08/2002
Toledo Blade


A moderate fish-kill in western Lake Erie last week off Port Clinton is under investigation by the Ohio Division of Wildlife amid an ongoing, deadly epidemic of botulism in eastern Lake Erie.

State fisheries biologists are relatively certain that the western basin kill - of between 1,000 and 2,000 small freshwater drum, or sheepshead - is unrelated to problems down east. But fisheries agencies lakewide are on alert because of the extent of kills in New York, Pennsylvania and Ontario waters.

Last summer hundreds of thousands of fish were killed in the eastern basin, including everything from trophy smallmouth bass and rare lake sturgeon to sheepshead (drum), walleye, rock bass and tiny stone cats.

Thousands of waterbirds, including several species of gulls, highly prized common loons, mergansers and sanderlings, a shorebird, also succumbed.

The toll also included bottom-dwelling salamanders called mud puppies. Analyses showed the deadly poisoning extended even to insect and midge larvae, which are eaten by small fish.

The cause of the kills was traced to a major outbreak of botulism type E.

Cooler weather last autumn and winter cold shut down bacterial activity. But the renewed hot weather and warmer waters this summer again have cranked up the outbreak in eastern lake areas.

So far this summer thousands more mud puppies - which grow to 14 inches and include fish in their diet - have been killed in the eastern basin.

Last week’s western basin fish kill, between South Bass Island and Catawba Island peninsula, is limited to what appeared to be one large school of three to four-inch drum - last year’s hatch, said Roger Knight, supervisor of the division’s Lake Erie Fisheries Research Station at Sandusky.

The fact that it involves just one species of fish in one size in one place leads him to strongly suspect that botulism is not involved here and now. Botulism would affect many species and sizes.

Nonetheless, about 200 of the dead drum have been frozen and saved for laboratory analysis.

"Pathogens exist in any environment, including aquatic systems like Lake Erie," said Knight. In short, he added, "fish can get sick - they’re just like us." Fungus and bacteria naturally are present in the water and if a fish’s resistance is low for some reason, an infection can set in.

Knight said that he has examined some of the dead drum and nothing is externally visible to suggest a cause of death. "They were too small to be caught and too many of them in one place to account for fishing mortality."

The biologist added that commercial fishing error cannot be blamed, either. Seining season ended June 14 and no trapnets are set in the area. Nor were any chemical spills noted. "For now I am leaning toward a natural phenomenon."

Juvenile fish such as the drum involved can be killed by thermal shock, involving extreme variations in water temperature, Knight explained.

A thermocline, unusual for early summer, had set up in the western basin because of the long, cold, wet spring followed by the sudden hot spell and calm weather of mid to late June. A thermocline is a marked layering of colder, heavier water beneath a much warmer upper layer.

The cooler weather and accompanying northeast winds that set in by Friday, however, are expected to stir and mix the shallow western basin and eliminate the current thermocline, Knight said.

"This has been a weird weather-year. It’s affected everything from turkey hunting [poorer than expected] to fishing."

State wildlife officers and biologists from Sandusky spent several days searching the western basin for additional sizable fish kills, without result.

"We want to know about mortalities," Knight stated. Fresh kills make the best samples.

The eastern basin kill of mud puppies has been "pretty impressive," said Don Einhouse, a biologist with New York’s Lake Erie Fisheries Research Station at Dunkirk. He said that a few reports of dead gulls also have filtered in, and more kills of drum and smallmouth bass, while not large, are conspicuous.

Wildlife pathologists still are testing samples from the eastern basin this summer, Einhouse said. No cause has been confirmed, but botulism is suspected.

One of the things complicating the situation is that periodic kills occur naturally, and they are related to temperature upwellings in the basin or low or no dissolved oxygen in some other areas of the lake, the New York biologist said.

"[But] clearly something different is in the mix now." Einhouse said it is puzzling why the botulism kills have been limited thus far to the eastern basin.

The best news is that two research projects, by researchers at Cornell University and State University of New York-Fredonia, have been initiated to explore the causes and pathways of the outbreak, Einhouse said. "There are a lot more questions than answers at this point."

Until the mechanism is known, an intervention - if at all possible - cannot be designed.

The bacteria are everywhere in the lake, so the question remains as to what special circumstances have coalesced to allow formation of the type E toxin that actually does the fatal poisoning.

Einhouse said that leading suspicions revolve around the changed food web in the lake in recent years, which involves prolific alien pest species, including zebra mussels and their deepwater cousins, quagga mussels, and round gobies, a small bottom-dwelling pest fish.

Gobies eat the mussels, and mud puppies and larger fish eat gobies.

Which brings the problem full circle back to the western basin., which is loaded with zebra mussels and gobies as well. "We’ve got mud puppies here and yet we’re not seeing kills," noted Ohio’s Knight.

Knight urges lake anglers to call in sightings and locations of large fish kills to the Sandusky Station, 419-625-8062. Biologists are not looking for the odd dead fish here or there, but a visible clustering of dead fish in a set area.
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