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Bear Lake’s sterile lake trout are headed to other Idaho lakes

Biologists looking to determine whether the lake’s fertile non-native trout have been reproducing.

(Photo courtesy of Utah Division of Wildlife Resources) Utah DWR fisheries technician Emily Wright displays a massive lake trout caught and released in Bear Lake during a gillnetting survey in 2019.

Lake trout have owned the top rungs of the Bear Lake food chain for decades, ever since the long-lived predatory species was introduced into the mountain lake straddling the Utah-Idaho state line.

These large trout became a favored sport fish for the anglers who flock to Bear Lake, but the species is hard on the lake’s native fish, including four that live nowhere else. Since 2001, Utah fisheries managers have been stocking non-reproducing sterile lake trout in the hopes of keeping their numbers in check while maintaining the popular sport fishery.

But many questions remain, and this summer Idaho and Utah wildlife officials hope to get answers by netting hundreds of these lake trout for study and translocation to another Idaho lake.

The research project, funded mostly by Idaho, is designed to assess the effect of 20 years of stocking sterile lake trout on the size distribution, age and the portion of fertile to sterile fish in the lake trout population, according to Randy Oplinger, sport fisheries coordinator with the Utah Division of Wildlife Resources, or DWR.

“We have assumed, because there’s not a huge population of lake trout, that reproduction of lake trout is pretty minimal. What we don’t have a firm grasp on is, are these fertile fish actually reproducing,” Oplinger said. “That would be an issue because if they’re reproducing, It means that we’re still having a handful of these fertile fish and we’ve got the potential for future reproduction.”

Lake trout were first introduced in Bear Lake in 1911 and the state has continued to stock them over the years.

“We were just looking to add a sport fishery. We weren’t considering some of the native fish issues at the time,” Oplinger said. “Bear Lake would be a classic lake trout-kind of fishery, cold deep water.”

(Tribune file photo) The Bear Lake Marina is a popular and busy place during the summer months.

Because of the lake’s chemistry and lack of spawning habitat, however, it has been assumed that this lake trout population would die out without stocking. But is that assumption accurate? This summer’s study is hoped to determine whether Bear Lake’s fertile lake trout have been reproducing.

Bear Lake is also home to Bear River cutthroat trout, as well as four endemic fish: Bear Lake sculpin, Bear Lake whitefish, Bonneville whitefish and Bonneville cisco.

Lake trout can co-exist with these natives, but it requires careful management, according to DWR. Its goal for Bear Lake is for its lake trout population to be entirely sterile. The new study will document progress toward reaching that goal.

For about 10 days in June, a contractor will drag the lake’s waters with a gill net and pull up lake trout. The fish will be weighed and their blood will be test to determined whether they are fertile or sterile.

“The large nets and short timeframe will allow us to collect more fish, while minimizing any impacts to the lake trout collected, as well as to any other fish that we may catch in the nets,” said Greg Schoby, a regional fisheries manager with Idaho Department of Fish and Game.

Idaho will keep 400 sterile fish to stock in Stanley Lake in central Idaho. The rest of the netted fish will be returned alive to Bear Lake. The removed fish represent about 10% of Bear Lake’s adult population, according to Oplinger.

Most years, Utah plants about 17,000 young hatchery-raised sterile lake trout in Bear Lake. Through creel surveys, Oplinger said, DWR estimates anglers catch about 500 a year. The creel limit is two for Bear Lake’s lake trout.

“The mortality rate of the stocked lake trout is high,” Oplinger said. “They grow slowly and it normally takes 4 to 5 years for the fish we stock to reach a size where they are caught by anglers.”

(Brian Maffly | The Salt Lake Tribune) Stanley Lake in central Idaho.

Native to the Midwest and Canada, lake trout were introduced into the West’s high-elevation lakes, including Flaming Gorge Reservoir, where they have flourished, often at the expense of native cutthroat and nonsport species.

Yellowstone National Park has been struggling to rid its big namesake lake of illegally introduced lake trout for years, but without much success. The proliferation of lake trout has led to a decline in cutthroat trout, which in turn has disrupted not only a popular fishery, but also an important food source for bears and other wildlife.

Problem lake trout also roam central Idaho’s Stanley Lake in the Sawtooth National Recreation Area, where many visitors go specifically to fish for them. However, Idaho hopes to restore that lake’s endangered sockeye salmon run at the headwaters of the Snake River, but that may not be possible if the lake is dominated by a self-sustaining population of predatory trout, according to Carson Watkins, a fisheries manager with the Idaho agency.

So Idaho has been removing lake trout from Stanley Lake and intends to replace them with sterile adults harvested from Bear Lake.

“The idea is to replace the fish that were removed with a more benign alternative of stocked fish,” Watkins said. “We want to maintain that fishing opportunity, but we want to do that in way that we don’t compromise our sockeye recovery goals.”

Idaho is hoping to recover sockeye at three other popular lakes in the Sawtooths. Those lakes, however, are not burdened with lake trout.

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