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Researchers use dead fish to kill lake trout embryos

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JACKSON, Wyo. (AP) – Dead fish are being used to kill lake trout embryos in an experimental method to combat a threat to a native Yellowstone Lake species.

Researchers successfully killed all the embryos in an experiment using hundreds of lake trout carcasses, reported the Jackson Hole News and Guide.

If the method proves viable on a large scale, it could be a key tool in the fight to help cutthroat stage a comeback and rebound to their historical numbers. In turn, park managers hope to restore a multi-level trophic cascade that could, in theory, result in grizzly bears eating fewer elk calves.

Yellowstone Fisheries Supervisor Todd Koel introduced the carcass experiment.

“We were just trying to create an extremely negative environment for lake trout embryos to survive, and one idea was to use carcasses,” Koel said. “They caught 350,000-plus this year, and we dump them back into the lake anyway.”

The method could be used on a larger scale depending on its success.

“We were killing the embryos at up to a 100 percent rate inside of three weeks,” Koel said. “It far exceeded our expectations.”

Chris Guy of the Montana Cooperative Fishery Research Unit says fungus from the dead fish may be what killed 100 percent of the embryos in the experiment.

“We tried killing embryos just with a tarp, and we couldn’t get the dissolved oxygen to go down enough,” he said. “Now we put the lake trout carcasses on and we get 100 percent mortality in about three weeks and that, to me, corroborates fungus.”

Researchers including Northern Rocky Mountain Science Center biologist Bob Gresswell are also trying to track where lake trout spawn.

“What we’re learning is that we’re seeing some very site-specific places, and it’s much more dispersed than I originally anticipated,” Gresswell said. “Certainly we’re coming close to knowing more where the general spawning areas are, but the specifics within those sites is a little trickier. That’s the $64,000 question: Where are those spots? And can we develop some kind of technique that maybe is useful?”

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