It’s just before 8 a.m. on August 6 when the boat reaches the first gillnet of the day. I’m on Swan Lake volunteering with a recently revived effort to knock down the lake’s invasive lake trout population and stem the decline of its famous bull trout. We’re into fish from the get-go. Tom Short, an employee for Hickey Brothers Research, operates the commercial net hauler, while his partner picks lake trout from the netting that the duo set the night before. This first net was set to target small lakers—and every couple of seconds, one of them rises from the deep.
Carter Fredenberg, a biologist for the U.S. Fish and Wildlife Service (USFWS), measures each catch, while Kassandra Cole, his counterpart on the Montana Fish Wildlife and Parks staff, marks the numbers down. Then, Fredenberg either bonks the live fish and gives them to volunteers to gut or throws the already-dead ones in a cooler. The fish caught alive will be donated to local food pantries in northwest Montana, while the already-dead ones will go to a raptor recovery center. I’m one of the volunteers wielding a fillet knife on the back of the boat.
It's a fast-moving, efficient operation, and within the first hour, we’ve processed over a hundred nonnative fish. Soon, we’ll move to nets targeting bigger specimens. Over the span of three weeks, the operation will remove more than 2,000 of them from the glacial lake. But will it work?
The History of Bull Trout in the Swan Valley
The bull trout, like brook trout, are actually a species of char. The fish is native to the Pacific Northwest, Canada, and Alaska. It grows to epic proportions compared to other trout and often preys on small cutthroats. It’s one of the most iconic species in the Northwest U.S.—and one of the most imperiled.
That's because bull trout are particularly sensitive to rising water temps, predation, and competition from nonnative species. They're also heavily impacted by pollution, low flows, and physical barriers that prevent them from migrating from large lakes and rivers, where they winter, into the small tributaries where they spawn. The migratory behavior of the fish is one reason summer gillnetting doesn’t lead to significant bycatch.
The USFWS listed bull trout as Threatened under the Endangered Species Act in 1999, which closed most angling opportunities for the species. But there was one exception from the listing in the state of Montana—a historic stronghold for bull trout. That was Swan Lake, a 3,300 acre glacial lake between Seeley Lake and Bigfork, Montana. At the time, it was the crown jewel recreational bull trout fishery in the region and for a time, and the only one in the area. Scientists were particularly impressed that the bull trout population remained strong given heavy logging in the area.
But that changed quickly after lake trout were first recorded in Swan Lake in 1998. Fisheries biologists introduced Mysis shrimp there in 1975 in a move meant to bolster a recreational kokanee fishery. But that inadvertently created conditions for lake trout to quickly grow large enough to prey on juvenile bull trout.
Bull trout numbers started to drop, evidenced by declining redd—or spawning bed—counts, which went from over 800 in the late 1990s to fewer than 400 in 2010. In response, federal and state officials instituted an experimental gillnetting program. They removed nearly 60,000 lakers between 2009 and 2016 when the program was discontinued because of a lack of funding and pushback from anglers who wanted to target the lakers. At the time, the lake’s bull trout population appeared to stabilize.
It didn’t last, though. In recent years, redd counts have continued declining to the lowest levels in decades—and officials say that the biggest culprits are nonnative lakers. “The lake trout population kept increasing, and it had a very negative effect on both kokanee and bull trout,” says Mike Hensler, FWP Region 1 Fisheries Manager. “We think we have a remedy. The gillnetting will help the kokanee, too, which is important. They’re like candy bars to the bull trout. And historically, people really loved to fish for kokanee here.”
What Makes the Revamped Program Different
The revival of gillnetting comes at a critical time for bull trout in the region. The other strongholds for the species in Montana—the South Fork of the Flathead River drainage and Lake Koocanusa, along the border of British Columbia—are experiencing declines too. Those places have issues with pollution and drought, and there’s not a lot that fishery managers can do to address those issues. Swan Lake, on the other hand, is a place where they can make a difference.
According to Fredenberg, the bull trout's declining status adds a sense of urgency to the work. “Having a redundancy of populations is important,” he says. “Losing a population is a loss in redundancy. When you have the possibility of whole populations blinking out, it makes each one more valuable.”
The current effort, supported through a federally-funded State Wildlife Grant, has several key differences from past gillnetting attempts. For one, FWP has a biologist specifically dedicated to it in Cole. In past efforts, officials placed nets in randomized areas as part of research projects; this time, experienced commercial anglers are placing nets to strategically catch as many fish as possible to focus on suppression.
The project has one “gold example,” Cole says. That’s Yellowstone Lake, where researchers have shown that it’s possible to limit lake trout populations to conserve native species—but that doing so requires a concerted and extended suppression effort. In Yellowstone, gillnetting efforts have saved scores of cutthroat trout from lake non-native trout predation; researchers hope similar impacts will apply to bull trout if they can remove a specific amount of lake trout biomass per hectare.
Related: Our River: Meet the Hunters and Anglers Fighting to Save the Klamath River Basin
This season, Cole says they'll exceed the goal, which is a good sign for the program’s prospects. “I grew up in Montana. My family is from here,” he says. “It’s not often that you have a fish that is so unique to an area. We want to bring back the opportunity for folks to encounter and experience this amazing fish for years to come.”
