Fish Trophic Interactions As Indicators of Climate Change in the Great Lakes

Lake Erie resource management goals include sustaining populations of economically valuable cool-water species such as percids, in part, via regulation of nutrients to achieve mesotrophic conditions.  Via indirect effects on habitat, climate-driven increases in water temperature over the past half-century may impede efforts to achieve this goal.  To provide insights on potential future trophic status, we investigated distribution, diet, prey availability, and stable isotopes for fish communities from mesotrophic and oligotrophic sub-basins of Lake Erie during 2011 to 2013.  In general, spatial variation was greater than temporal variation, with trends of lower fish and zooplankton diversity, lower total biomass, lower diet overlap, and lower contribution of pelagic primary production in the oligotrophic sub-basin.  Seasonal effects were most prominent during hypoxic episodes, and in contrast with expectations of avoidance, hypoxia tended to concentrate fish and increase catch rates near edges of the hypoxic front.  In both sub-basins, non-native Rainbow Smelt exhibited a disproportionately high abundance relative to their intermediate trophic level, highlighting the hypothesis that they may exert middle-out control of the fishery food web in central and eastern Lake Erie.  Our findings have implications throughout the Great Lakes where various sub-basins are impacted by cultural eutrophication.