Diet and trophic ecology of introduced salmonines at two south shore ports of Lake Superior, 2019

Abstract Introduced salmonines (Oncorhynchus spp. and Salmo spp.) are important components of recreational fisheries in the Great Lakes. These fishes were stocked heavily following the fishery collapse of lake trout (Salvelinus namaycush) due to sea lamprey (Petromyzon marinus) predation and commercial overharvest. While salmonine introductions occurred in all five of the Great Lakes, Lake Superior is less productive than the lower Great Lakes restricting most introduced salmonines to a small percentage of available habitat. This suggests the potential for high resource overlap between salmonines, yet little information has been published related to the trophic ecology of introduced salmonines in Lake Superior. Furthermore, hybrid splake (S. namaycush × S. fontinalis) are also stocked by various state agencies while little information on their trophic ecology exists. To address uncertainties associated with introduced salmonines, we assessed the diet composition and isotopic niche overlap of fish collected from two south shore ports of Lake Superior. Introduced salmonines consumed similar prey items including rainbow smelt (Osmerus mordax), coregonines, and three-spined stickleback (Gasterosteus aculeatus) in varying amounts, with a notable percentage of diet comprising terrestrial invertebrates. These results are further supported by stable isotope analysis which indicated high isotopic niche overlap among introduced salmonines suggesting a mixed diet attributed to benthic, pelagic, and terrestrial sources. Our characterization of the salmonine community provides important information that will inform fisheries research and management in Lake Superior.