Ugly Discovery at Swan Lake

Ugly Discovery at Swan Lake

The Fish and Wildlife Commission takes an unprecedented step to stop illegal fish introductions after walleyes are found in a scenic northwestern Montana lake. By Tom Dickson.

This story is featured in Montana Outdoors May-June 2016 issue

Last October Leo Rosenthal was working with a commercial netting crew to remove lake trout from Swan Lake. As the workers pulled fish from a mile-long gill net used to capture lake trout spawning on shallow underwater reefs, a crew member called out to Rosenthal that he’d found a walleye in the mix. Never before had that species been documented in Swan Lake. “Of course it was disappointing,” says Rosenthal, FWP fisheries biologist for Swan Lake. “But I can’t say I was surprised.”

Disappointing, because the 17-inch walleye—along with another of the same size netted a week later—could indicate the presence of a reproducing population in the scenic lake, which sits across the Mission Mountains from Flathead Lake in northwestern Montana. If they became established, walleyes could threaten the lake’s famous kokanee salmon and bull trout populations. Both species are already under siege from overabundant non-native lake trout. FWP has been testing removal techniques on the voracious lakers by contracting with commercial netters for the past seven years.

Rosenthal’s lack of surprise came from knowing that illegal fish introductions are increasing. FWP has documented more than 500 illegal introductions in lakes, reservoirs, ponds, and rivers since the 1980s. The Swan Lake planting is the 11th illegal walleye introduction that FWP has documented west of the Continental Divide, and it’s likely other attempts have been made but remain undetected. “Far too often we’ve seen non-native fish show up in lakes where they’ve never before been found, putting existing fisheries at risk,” Rosenthal says.

Swan is one of only a handful of lakes in Montana containing a robust population of bull trout, a federally threatened species. The lake is also home to a popular kokanee fishery. The small salmon, averaging 10 to 12 inches long, are considered delicious and often bite eagerly.

The only good news from Swan Lake is that the two walleyes did not originate there. When FWP scientists analyzed chemicals in the growth rings of the fish’s ear bones, or otoliths, they found that the three-year-old walleyes did not grow up in Swan Lake. Rosenthal says that if the fish had originated from Swan Lake, that meant a reproducing population had established itself. “That’s not to say there isn’t one there now,” he says. “But at least it’s still only a possibility and not a certainty.”

FWP biologists are comparing chemical traces in otoliths of fish in other Montana lakes to those in the two walleye otoliths to see if they can learn where the illegal fish originated. “Then we can focus attention on that lake and see if we can find out, maybe through a call to our TIP-MONT hotline, who made the illegal introduction at Swan Lake,” says Mark Deleray, FWP regional fisheries manager in Kalispell.

Worrisome trend
Other illegal fish introductions have threatened fisheries across western Montana, particularly in the Seeley-Swan Valley. In 2014 smallmouth bass were illegally placed in Seeley Lake. Northern pike were unlawfully dumped into Salmon and Seeley Lakes in the early 1990s. The pike have since spread downstream into the Blackfoot and Clark Fork Rivers, where they feed on brown, rainbow, and cutthroat trout. Illegally planted non-native brook trout have damaged Clearwater Lake, one of Montana’s top westslope cutthroat fisheries.

In Noxon Rapids Reservoir, on the lower Clark Fork near the Montana-Idaho border, illegally introduced walleyes threaten the lake’s renowned smallmouth bass, largemouth bass, and perch fisheries, as well as west-slope cutthroat and bull trout populations. Biologists report that walleyes and other predator species have already put a big dent in forage fish populations such as peamouth, yellow perch, and northern pikeminnow.

Deleray says anglers who illegally introduce new predator species might believe that the new species simply provide additional recreation. “But those fish actually decrease fishing opportunities by taking food away from existing fish,” he says. “These lakes already have a natural balance between predator and prey fish. Add more hungry predators like walleye to Swan Lake and they could impact the kokanee population, a food source for bull trout.”

New species can ruin existing fisheries, robbing other anglers of recreational opportunity and threatening native fish populations and federally protected species. “When we are forced to go in and try to fix the problem, it’s extremely expensive work, and then all anglers get stuck with the bill,” says Bruce Rich, head of the FWP Fisheries Division.

Cash for convictions
Alarmed over the threat to popular, economically valuable fisheries, the 2011 Montana Legislature doubled the fine to $10,000 for those convicted of illegally introducing fish. Lawbreakers could also face jail time.

Unfortunately, catching someone in the act is difficult. Most lakes are in sparsely populated areas, where fish can be easily transferred from one lake to another without notice. To encourage citizens to turn in skofflaws who illegally transport fish, major conservation groups and outfitting organizations have pledged a total reward of more than $20,000 for information leading to successful prosecution. The Fishing Outfitters Association of Montana, Invasive Species Action Network, Montana B.A.S.S. Federation Nation, Montana Pike Masters, Montana Trout Unlimited, Montana Wildlife Federation, Walleyes Forever of Montana, and Walleyes Unlimited of Montana contributed to the reward. Another $1,000 is available through FWP’s 1-800-TIP-MONT violation report line. Montana Trout Unlimited is also offering an additional reward of $10,000 for tips leading to the conviction of those who illegally introduced walleyes into Swan Lake, walleyes into Noxon Rapids Reservoir, or smallmouth bass into Seeley Lake.

Bruce Farling, TU Montana director, says his members are angry. “We’ve spent decades working with landowners, FWP, communities, and other anglers to protect and restore coldwater fisheries, and then all that work is compromised by the selfish acts of a few criminals,” he says. Bob Gilbert, executive director of Walleyes Unlimited of Montana and a former state legislator, notes that his organization has long denounced illegal fish planting. “We adamantly oppose anyone taking the law into their own hands,” he says.

Playing hardball
In December 2015, the Fish and Wildlife Commission took an unprecedented step by requiring anyone who catches a walleye in Swan Lake to kill it immediately and then turn the entire fish over to FWP. “The regulation is meant as a major disincentive,” says Deleray. The new law prevents anglers from taking their catch home to eat. And those who prefer to catch walleyes and then release them to grow larger won’t benefit either because the new must-kill requirement prevents establishment of an illegal trophy fishery.

“This is hardball, no doubt about it,” says Deleray. “It shows how seriously the commission and we in FWP take this issue. To those thinking about making illegal fish introductions, this regulation is saying, ‘Don’t take the risk, because you won’t get what you want out of it.’” Bear bullet

Tom Dickson is editor of Montana Outdoors.