AUTHORS: Brandon Gerig1, School of Freshwater Sciences, University of Wisconsin-Milwaukee, 600 E Greenfield Avenue, Milwaukee, WI 53204. Email: gerig@uwm.edu
Troy G. Zorn Michigan Department of Natural Resources Fisheries Division, Marquette Fisheries Research Station, 484 Cherry Creek Road, Marquette, MI 49855, USA. Email: zornt@michigan.gov
Kevin Pangle, Central Michigan University, Department of Biology, 1455 Calumet Court, Mount Pleasant, MI 48859, USA. Email: pangl1k@cmich.edu
Nick Peterson, Minnesota Department of Natural Resources, Lake Superior Area Fisheries, 5351 North Shore Drive, Duluth, MN 55804. Email: nick.peterson@state.mn.us
Henry Quinlan U.S. Fish and Wildlife Service, Ashland Fish and Wildlife Conservation Office, 2800 Lake Shore Drive East, Ashland, WI 54806, USA. Email: henry_quinlan@fws.gov
1Presenting author
ABSTRACT: Abstract Identifying streams that host scarce migratory salmonid life histories, such as coaster brook trout, is challenging due to the lack of inexpensive, non-lethal techniques for confirming Great Lake to stream migrations from observations of fish from a single sampling event. We examined prior foraging (and inferred residency) of brook trout using stable isotope analysis of fin clip tissue from 589 fish captured in Lake Superior or tributaries with vs. without access to Lake Superior. We observed strong isotopic separation in δ13C brook trout between Lake Superior and Lake-inaccessible reaches and developed a linear discriminant function (LDF) which assigned fish to these environments with over 97% accuracy. LDF and Bayesian stable isotope mixing models used to estimate stream and lake energy sourcing by brook trout collected from Lake-accessible reaches identified stream of origin and brook trout length as significant covariates influencing energy sourcing. Brook trout caught in Lake-accessible reaches had isotope signatures and sizes that were intermediate to fish from Lake-inaccessible reaches and Lake Superior, potentially indicative of Lake Superior to stream migrations or possibly an energy subsidy from adfluvial migrants in streams. The LDF was used to estimate the probability that recently grown fin tissue from brook trout collected in Lake-accessible reaches resulted from foraging in Lake Superior, with data on fish length and probability of Lake Superior assignment (Pr) used to identify tributaries with “likely” coaster brook trout. However, further research is needed to distinguish between Lake Superior-based foraging and subsidy effects from adfluvial fishes.
