AUTHORS: Heidi M. Rantala, MN Department of Natural Resources, Fisheries Research; Nick Peterson, MN Department of Natural Resources, Lake Superior Fisheries; David R. Burge, St. Croix Watershed Research Station, Science Museum of Minnesota
ABSTRACT: Minnesota tributaries to Lake Superior are unique systems with glacial relict fish communities, including Brook Trout (BKT). Fish habitat in these streams is vulnerable to change, given the sensitivity of the systems. With limited groundwater inputs, hydrology is driven by precipitation and snow melt, and the streams lack buffering capacity to warming temperatures. Stream conditions are favorable to the mat-forming diatom, Didymosphenia geminata, which was detected in multiple of the northern-most streams along the Minnesota shoreline since 2018. Here, we present analyses of diets from BKT, naturalized Rainbow Trout, and several other fish species in four North Shore streams from three seasons in 2023. Fish diets were sampled from resident and migratory individuals, both young-of-year and older fish, from above (BKT only) and below natural barriers between Lake Superior and upland waters. Additionally, two of the four streams had prolific, localized Didymosphenia mats during the sampling period. As expected, we observed spatial and temporal variability in the both the diet items and amount of prey through the sampling season, as well along a stream reach. These data provide baseline information for managers to increase understanding of the ecology and status of these populations in Minnesota waters.
