Muskies are escaping reservoirs over dams; flashing lights or bubbles might not stop them

By on June 14, 2014
The opposite of the problem that prompted Stewart's study: a muskie trying to jump Vilas Dam (Credit: Richard Hurd)

As many as 25 percent of the muskie stocked in some reservoirs are escaping over dams and swimming downstream, away from their intended fisheries. A new study shows that the standard first line of defense for deterring fish movement may not be enough to corral them.

A 2013 study estimated that a quarter of the muskies in Lake Sam Dale in Southern Illinois escaped over its dam in the course of a year. It’s reasonable to assume that the same thing is happening in reservoirs across the midwest, according to Heather Stewart, faculty research assistant at Oregon State University and the Oregon Cooperative Fish And Wildlife Research Unit. That’s bad news for fishery manager and anglers alike.

“They’re fairly expensive to produce, so it gets to be costly when you’re constantly restocking these reservoirs so that people can fish them,” Stewart said. “It also affects their size structure when these larger fish are escaping and you just have these smaller fish that people aren’t really wanting to go after as much.”

It also introduces the predatory muskie into downstream habitats, where they can take a bite out of native species.

Fisheries and reservoir managers have ways of making fish go where we want them. Though physical barriers like nets can be expensive and vulnerable to floating debris, studies have shown low-cost strobe lights and bubble curtains can repel species such as Chinook salmon, largemouth bass and yellow perch.

Heather Stewart pictured here with one of her good fishing buddies

Heather Stewart pictured here with one of her good fishing buddies

But until recently, those methods hadn’t been tested on muskie. Prior to working at Oregon State, Stewart led research at the University of Illinois at Urbana–Champaign (partnering with the Illinois Natural History Survey) that tested how well a bubble curtain and strobe light could prevent juvenile muskies from topping a miniature dam built in the laboratory.

They pumped air through submerged, perforated PVC and flashed a strobe light once per second, both on their own and in combination. They watched with video cameras to stay out of the muskies’ sight to better judge whether the bubbles and light could keep the fish from swimming over the dam.

They couldn’t.

“We actually found that the strobe lights seemed to attract the fish to the barrier, which is not ideal,” Stewart said.

The model spillway used in the study

The model spillway used in the study

The muskies’ behavior before making the leap made it clear that the flow over the dam wasn’t just sucking up helpless fish. The muskies generally propelled themselves over, and some swam over to check the dam out a few times before before taking the plunge.

“Some of the fish actually jumped out of the water to go over the dam,” Stewart said. “To me that says fairly obviously that they wanted to get over.”

The researchers flashed the light as fast as their equipment allowed, so future research might find that more intense strobe might be more effective, Stewart said.

Stewart grew up in Illinois but did her muskie fishing in Wisconsin.

“Most of the muskie fishing I did in Illinois was electroshocking, so that doesn’t count.”

Top image: The opposite of the problem that prompted Stewart’s study:  a muskie trying to jump Vilas Dam (Credit: Richard Hurd, via Flickr)

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