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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