The great Flathead fish fiasco 

State and tribes disagree over how to handle invasive lake trout

The ding! is soft, but Capt. Rod’s response is Pavlovian, and he skips over to the charter boat’s console with a nimbleness remarkable for a man his size. “Fish on two!” he calls. He hurries back to the stern and pulls the appropriate rod from its sleeve, then hands it to me. “Okay, reel her in,” he says.

I steel myself for battle, but this particular fish, a lake trout, is blasé in the face of death. I reel. It resists a little. I reel again. It tugs, kind of. After a minute or so, Rod scoops the trout out of Flathead Lake and hands it to me. Jim Vashro, an avuncular biologist with Montana Fish, Wildlife and Parks, appraises it with a practiced eye.

“If you want to be respectable, say ‘Less than 10,’” he advises.

He means pounds, and he is certainly right. But respectable or not, my catch is still compelling. It is a prism of a fish: recreational bounty, invasive pest, windfall, scourge, everything between. And it is the subject of a spirited debate about how best to manage the species, not only because of its appetite for threatened fish, but also its absolute dominance here in Flathead Lake and west of the Continental Divide.

Such a fight over a flaccid fish. And here one hangs, its fate in my hands.

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  • Pumpernickel Stewart

Early in the 20th century, biologists believed only 10 species of native fish lived in Flathead, the West’s largest natural freshwater lake. But anglers and game officials had already introduced other species.

“It was a Johnny Appleseed approach,” Vashro says. “Throw in lots of stuff, see what makes it.”

In 1920, a shipment of kokanee arrived from Bonneville, Ore. By 1940, kokanee, which are landlocked sockeye salmon, had replaced cutthroat trout as the most-caught fish, and they remained dominant until the 1980s.

Meanwhile, the lake trout, introduced from the Great Lakes in 1905, bided its time. “There are many cases in which a species arrives and it just sits around,” says Daniel Simberloff, an authority on invasive species at the University of Tennessee. Then, he says, something changes to trigger a rapid expansion. In Flathead Lake, it was Mysis shrimp. Starting in 1968, state fisheries managers released the shrimp in several lakes of the Flathead watershed to enhance kokanee stocks; the shrimp moved downstream and reached Flathead Lake in 1981.

Instead of being a boon, though, Mysis competed with kokanee for their preferred food, zooplankton. The kokanee population collapsed. More importantly, younger lake trout feasted on shrimp, and the population soared. They ate nearly all of the remaining kokanee, as well as any other fish they could get their mouths around. Today, an estimated 1.6 million lake trout live in Flathead; more have since migrated and colonized most of the watershed.

Many of the remaining native fishes in Flathead Lake have dramatically declined, including bull trout, the top native predator. The Flathead watershed is the species’ regional stronghold, although it is found in cold streams and lakes from Montana to Oregon to the Yukon. As a fish, it is not especially flashy. Adults are olive-green with a creamy belly and light spots on their back and sides. (When they spawn, though, the green saturates almost to black, the belly to a smoldering ember orange.) But they share salmonids’ endurance. Some migrate to Flathead Lake from natal streams up to 130 miles away. There, they mature and grow before returning to their home streams to spawn; unlike Pacific salmon, they survive the journey, and may repeat it several times during their life.

Dams and logging hit bull trout hard, but lake trout were a new kind of threat, devouring young bull trout and outcompeting adults. The lake trout could also live 30-40 years to a bull trout’s 12-15, and spawn, as their name implies, in lakes.

By 1996, just 1,300 bull trout survived in Flathead Lake. Two years later, they were listed as threatened under the Endangered Species Act. Scientists now estimate that the population is slightly higher, with somewhere between 3,500 and 5,000 left.

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