Wednesday, September 12, 2012

Lake Erie fish kills are weather-related

Moderate to large fish kills observed Tuesday off the Chagrin River, Perry Township Park, and Ashtabula Harbor all appear to be death by natural causes.

A combination of sour weather, normal and seasonal fish species migration and the mixing of the lake’s nearshore water column all contributed to the death of the fish, says a state fisheries expert.

“Think of Lake Erie’s Central Basin as a bathtub,” says Kevin Kayle, supervisor of the Ohio Division of Wildlife’s Fairport Harbor Fisheries Research Station.

 “During the summer we see algae blooms of various kinds in the upper parts of the water column. As the algae dies, it sinks to the lake’s bottom where there is colder water.”

At the lake’s bottom lives bacteria, which consumes oxygen as it decomposes the algae, Kayle says.

“What happens in late summer is that the dissolved oxygen levels are reduced because the bacteria is using it all up,” Kayle said.

“And when you get a weather event like we saw last weekend with the severe storms that produced high wave action, there was a lot of mixing of the water.”

Many fish could not then quickly escape the low-oxygenated water, Kayle says.

Kayle did say that the vast majority of the dead fish were either fresh-water drum (sheepshead) or else gizzard shad; species of lesser concern to both sport anglers and commercial fishermen.

And each of these species is more vulnerable to such weather-and seasonal-related stresses “simply because of their location, which is near the bottom and near shore,” Kayle said.

“If we see more storms we could see more fish kills like this episode, too, and until the lake’s water fully mixes,” Kayle says.

- Jeffrey L. Frischkorn
Twitter: @Fieldkorn

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