Flathead Lake: Trophic Cascade

Mysis relicta under microscope
Introduced species have altered Flathead Lake’s biological community dramatically over the last 100+ years. Of particular note was the introduction of Mysis diluviana. This freshwater shrimp’s introduction resulted in dramatic food web changes that were documented by FLBS scientists.
Introduced widely in the 1960s and 1970s throughout Western North America as a food source for salmon and trout, in Flathead Lake the Mysis shrimp voraciously consumed zooplankton, the food of the kokanee salmon they were introduced to help. This unexpected effect resulted in the collapse of the kokanee population, which eliminated a reliable food source for hundreds of bald eagles and bears that annually migrated to the kokanee spawning grounds in the Flathead River system.

At the same time, populations of nonnative lake trout and lake whitefish, which were themselves an introduced species, exploded with Mysis shrimp as a food source. With the increase in both Mysis shrimp and lake trout, native bull and cutthroat trout populations have dramatically declined, and Flathead Lake’s fish community is now dominated by nonnative species. Additionally, as Mysis shrimp consume native zooplankton which eat algae, the amount of algae in Flathead Lake has increased.

Therefore, the introduction of Mysis shrimp not only influenced the biological community of Flathead Lake but also directly affected the lake’s water quality.

FLBS researchers were among the first to empirically document this Trophic Cascade in a lake ecosystem, and they continue to track the ongoing ecological effects.

Publications
  • Spencer, C. N., B. R. McClelland and J. A. Stanford. 1991. Shrimp stocking, salmon collapse and eagle displacement: Cascading interactions in the food web of a large aquatic ecosystem. BioScience 41(1):14–21.
  • Stafford, C. P., J. A. Stanford, F. R. Hauer and E. B. Brothers. 2002. Changes in lake trout growth associated with mysis relicta establishment: A retrospective analysis using otoliths. Transactions of the American Fisheries Society 131(5):994–1003.
  • Ellis, B. K., J. A. Stanford, D. Goodman, C. P. Stafford, D. L. Gustafson, D. A. Beauchamp, D. W. Chess, J. A. Craft, M. A. Deleray and B. S. Hansen. 2011. Long-term effects of a trophic cascade in a large lake ecosystem. Proceedings of the National Academy of Sciences USA 108(3):1070–1075. Full text