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Tracing habitat utilization of Muskellunge (Esox masquinongy) in the St. Louis River and Lake Superior using stable isotope ratios
Citation:
Hanson, G., J. Pinkerton, E. Schaeffer, K. Okeson, L. Miller, AND J. Hoffman. Tracing habitat utilization of Muskellunge (Esox masquinongy) in the St. Louis River and Lake Superior using stable isotope ratios. Minnesota-Dakotas Chapters of the American Fisheries Society, Fargo, ND, February 25 - 27, 2019.
Impact/Purpose:
Habitat-specific movements for long-lived migratory fish are important to characterize to better understand the effect of habitat quality on population dynamics and consequently ecosystem services. But, few studies have identified approaches that could be used to assess intra-population effects from habitat-specific contamination. We combined two techniques stable isotope analysis and genetic strain analysis to study movements of individual Muskellunge (which support a high-value recreational fishery) between a highly contaminated coastal tributary and relatively clean nearshore habitat. We demonstrate how the technique can be used to identify intro-population risk factors for increased exposure to contaminated habitat, and thereby affect ecosystem services.
Description:
Muskellunge (Esox masquinongy) are a migratory fish species that were stocked in the St. Louis River estuary (SLRE). However, Muskellunge migratory behavior within the SLRE and between the SLRE and Lake Superior is largely unknown, and abundance in the river system at any time influences its carrying capacity. Our goal was to use an intrinsic tag (carbon and nitrogen stable isotope ratios [SIR]) to determine diet contributions from different habitats in the SLRE and Lake Superior, and from this infer migratory behavior. We sampled fin tissue from a combination of angler- and survey-captured Muskellunge from 2015-2017 for carbon and nitrogen SIR. Fish were characterized by genetic strain (Minnesota vs. Wisconsin), size, and sex. Among the 350 fish sampled, we found a wide range of SIR values, corresponding to a diet based in the upper estuary, near Duluth-Superior, or in Lake Superior, as well as to diets based on a varying mixture of locations. Strain and size, but not sex, were significant factors influencing carbon SIR. That is, larger fish and Minnesota strain fish had SIR values corresponding to diets based on Lake Superior and adjacent habitat, while smaller fish and Wisconsin strain fish had SIR corresponding to diets based mostly within the SLRE. Carbon SIR distributions also indicate size-specific habitat utilization by Muskellunge within the SLRE. Angler-captured fish had a reduced SIR range compared to survey captured fish, indicating a sampling bias associated with summer angler behavior. We conclude that St. Louis River Muskellunge are feeding in Lake Superior waters but that the SLRE is their most commonly used feeding ground, and that both stocked strain and size influence habitat utilization.