Bio Station, Salish and Kootenai join forces on lake trout study

by Ian Withrow
| September 23, 2020 2:45 AM

Up until the late 1800s, around 10 native species of fish patrolled the waters of Flathead Lake, the most notable of which included westslope cutthroat trout and bull trout. Beginning in 1890, fisheries managers began introducing nonnative species to the food web to ‘improve’ Flathead Lake and generate more recreational fishing appeal. Since then, the biological community of the lake has been greatly and forever changed by the presence of nonnative species.

Today, the introduced species of lake trout, lake whitefish and Mysis shrimp dominate the food web, so much so that nonnative species—including bull trout and westslope cutthroat, Montana’s state fish—have declined dramatically.

In 2014, the Confederated Salish and Kootenai Tribes began aggressively removing nonnative lake trout from Flathead Lake in the hopes of restoring the populations of native fishes. To support local communities and help offset some of the costs of this effort, the harvested fish are sold around the US and help supply local food pantries.

On the surface, it all seems like a win-win-win…but there’s a caveat: The Flathead Lake food web has a mercury problem.

While the presence of mercury can be relatively common in certain rocks and soil, the mercury in Flathead Lake is likely due to atmospheric deposition from both human and natural sources. The mercury concentrations being observed here are similar to conditions being observed in the Antarctic, Arctic, and the Pacific Islands, where the only possible source is from global air movements. Once ingested by microorganisms, the mercury is subsequently consumed in increasing concentrations as it travels up the food web. This means that lake trout, now the dominant predator in the lake, have the highest concentration of methylmercury.

Once ingested by microorganisms, the mercury is subsequently consumed in increasing concentrations as it travels up the food web. The longer the food web (which is at times lengthened by the arrival of nonnative species), the more opportunity for increased concentrations of mercury. This means that lake trout, now the dominant predator in the lake, have the highest concentration of methylmercury.

Today, FLBS environmental economist Nanette Nelson and her FLBS colleagues, Bob Hall and Erin Sexton are joining forces with the CSKT Natural Resources Department and Salish Kootenai College with the aim of answering two questions: 1) How will the removal of lake trout affect methylmercury concentrations in other fishes in Flathead Lake, and 2) Does access to lake trout at local food pantries result in beneficial health outcomes?

The research project is being funded by the Environmental Protection Agency (EPA), which just last week announced the distribution of over $2 million in grants to 14 organizations, universities and government agencies in Washington, Oregon, Idaho and Montana. These grants are the first to come out of the Columba River Basin Restoration Funding Assistance Program, established by Congress in 2016 as an amendment to the Clean Water Act to address water quality issues by reducing pollution, including toxins that can accumulate over time in water, sediment and fish tissues.

Nelson said project results will be shared with the Tribes who will ultimately determine the use of the newly acquired data. One possibility might be the development of consumption guidelines for additional fish species, depending on research results.

“Our project will culminate with a half-day workshop,” she said. “We’re going to assemble tribal natural resource managers, health professionals and decision makers to develop a plan on how best to use the newly acquired data to benefit both human and ecosystem health.”

If the old adage is true, if we really are what we eat, then I for one rest easier in the knowledge that these significant research efforts are underway as an investment in food safety and the future of our complex yet incredible Flathead Lake food web—of which we are, if nothing else, tangentially a part.