Electroshock experiment at Yellowstone Lake spawning beds seemed to work, biologist says

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JACKSON, Wyoming — Biologists are making their first use of electroshock in their efforts to save native cutthroat trout in Yellowstone National Park from another voracious species of trout.

The electroshock treatment is being done to kill off lake trout that have invaded Yellowstone Lake when the unwanted fish is still spawning and in the earliest stages of its life.

Adult lake trout in Yellowstone can top 30 pounds, living almost exclusively on a diet of cutthroat trout, according to researchers.

Until now, netting of lake trout has been the park's main method of suppression for the past decade.

But new tactics being employed this fall by crews headed by park fisheries supervisor Todd Koel target the non-native fish in their spawning beds.

"The two tools that we used are still prototypes," Koel said. "One of them is electroshocking. It's an array that you move along the bottom.

"The other tool that we have," he said, "it's a placer gold mining suction dredge system."

That means park officials are attempting to electrocute lake trout eggs and are also trying to suck them out of cobble below Yellowstone Lake.

The results aren't yet in, as the lake trout suppression boats weren't pulled from the lake until about a week ago.

But Koel was encouraged and said there was "really good evidence" the electricity method was working.

In places where biologists tried the suction method over already-electrified spawning beds, most of the thousands of eggs and fry captured were dead, he said. Where the electricity had not yet been applied, the spawn were mostly alive.

"We saw what seemed to be really significant results just by using that test," Koel told the Jackson Hole News & Guide (http://bit.ly/1zS5Fwx).

Overall, the efforts to reduce the impacts of predatory lake trout on Yellowstone Lake's cutthroat trout are going well, U.S. Geological Survey research biologist Bob Gresswell said.

"Ultimately, this isn't about killing lake trout," Gresswell said. "It's about restoring cutthroat. What we really want to see is a response from the cutthroat."

After declining to a fraction of historic levels, the cutthroat appear to be bouncing back, Gresswell said.

"Cutthroat are becoming more abundant," Gresswell said. "They were getting caught by anglers off the shore."

Cutthroat were historically a vital food for bears each spring, and their decline has worried park officials.

Someday, Gresswell said, spawning bed treatments may be an integral part of the attempt to hold lake trout at low levels.

But biologists believe eradicating lake trout from the 136-square-mile lake is impossible.

"Gill netting won't go away," Gresswell said. "It'll be part of the scene, but within five years or so I think you'll see it cut back to a spring and fall activity. That would be my prediction."

If it proves effective, spawning treatment will "slowly, incrementally" become part of the lake trout suppression effort, Gresswell said.

Koel stressed that there are a few years of testing ahead before the spawning treatments are deployed around the lake. This year crews were simply getting familiar with the equipment.


Information from: Jackson Hole (Wyo.) News And Guide, http://www.jhnewsandguide.com

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