Research about Flathead Lake

USGS2026

Foodweb transfer and associated human exposure to methylmercury in Flathead Lake, Montana, USA

Reintroducing traditional foods into Indigenous contemporary diets can improve human health outcomes but may increase exposure to toxins, such as methylmercury (MeHg) in fish. This study examined the Confederated Salish and Kootenai Tribes (CSKT) Lake Trout ( Salvelinus namaycush [Walbaum, 1792]) suppression program in Flathead Lake, Montana, USA, a management strategy to restore the native fishery that may affect the food web and MeHg biomagnification rates. CSKT sells harvested Lake Trout ≤610 mm in length in local markets, donating a portion to local food pantries. We asked 1) To what extent do length and trophic level control MeHg concentrations in Lake Trout, Lake Whitefish ( Coregonus clupeaformis [Mitchill, 1818]), and Bull Trout (Salvelinus confluentus [Suckley, 1859]) in Flathead Lake? and 2) What are the health outcomes for Tribal women of childbearing age consuming fish fillets donated to local food pantries by CSKT? We calculated the MeHg biomagnification slope; modeled relationships between fish length, trophic position, and MeHg concentration; used probabilistic modeling to assess safe fish-consumption levels; evaluated fish-consumption habits of Tribal women; and estimated a benefit–risk quotient (BRQ) for Lake Trout. The MeHg biomagnification slope was 0.18 (CI: 0.17, 0.19), similar to oligotrophic, temperate lakes where Lake Trout are the top predator. Fish length and C and N isotope ratios explained 88% of the variation in log e (MeHg) concentration in Lake Trout. Fish-consumption rates among Tribal women were below federal MeHg exposure limits. Our models suggested 1 serving of Lake Trout per week poses minimal risk of exceeding MeHg intake guidelines. However, to meet essential fatty acids (EFA) intake recommendations, our BRQ analysis suggests Lake Trout should be consumed alongside fish with higher EFA and lower MeHg. Our interdisciplinary analysis suggests CSKT’s natural resource management strategy is likely a key factor in influencing MeHg accumulation in the Flathead Lake food web and subsequent transfer to people.

Montana↗

USGS2016

Lake trout ( Salvelinus namaycush ) suppression for bull trout ( Salvelinus confluentus ) recovery in Flathead Lake, Montana, North America

Non-native lake trout Salvelinus namaycush displaced native bull trout Salvelinus confluentus in Flathead Lake, Montana, USA, after 1984, when Mysis diluviana became abundant following its introduction in upstream lakes in 1968–1976. We developed a simulation model to determine the fishing mortality rate on lake trout that would enable bull trout recovery. Model simulations indicated that suppression of adult lake trout by 75% from current abundance would reduce predation on bull trout by 90%. Current removals of lake trout through incentivized fishing contests has not been sufficient to suppress lake trout abundance estimated by mark-recapture or indexed by stratified-random gill netting. In contrast, size structure, body condition, mortality, and maturity are changing consistent with a density-dependent reduction in lake trout abundance. Population modeling indicated total fishing effort would need to increase 3-fold to reduce adult lake trout population density by 75%. We conclude that increased fishing effort would suppress lake trout population density and predation on juvenile bull trout, and thereby enable higher abundance of adult bull trout in Flathead Lake and its tributaries.

Montana↗

USGS1982

Seismic reflection study of Flathead Lake, Montana

A seismic reflection survey of Flathead Lake, Montana, was carried out in 1970 to study the geologic structure underlying the lake. Approximately 200 km of track lines were surveyed resulting in about 140 km of useable data (Fig. 1). A one cu. in. air gun was used as the energy source. Navigation was by a series of theodolite sitings of the boat from pairs of shore-based control points.

Montana↗