Prey Species- and Size-Specific Consumption By Lake Michigan Piscivores

Invasive Alewives (Alosa psuedoharengus) have been an important diet item for salmonids in Lake Michigan for the last 50 years, especially for Chinook and Coho Salmon. However, over the past twenty years Alewife densities, growth rates, and condition have declined, evidently due to high predation pressure from salmonids and reduced pelagic production and invertebrate prey availability. Concurrently, another invasive forage species, Round Goby (Neogobius melanostomus), has increased in abundance and has become the second most common prey for some salmonids in Lake Michigan. We evaluated Lake Michigan piscivores by forage species, region and season using stomach content analyses. In addition, we examined size-specific consumption and the potential for individual specialization on specific prey species or sizes of prey. Collectively, Alewife and Round Goby constituted 99% of prey fish biomass consumed by the five main salmonid species during 2015-2016. The long-term sustainability of this predator-prey system may depend not only on tempering overall predation pressure, but also the partitioning of prey resources by species and size. We will summarize these findings and discuss their implications in the context of sustainable fisheries.