In Lake Erie, walleye (Sander vitreus) fishery recruitment is controlled by physical and biological processes acting on early life history stages; however, the impacts of recent, recurring cyanobacterial (Microcystis aeruginosa) blooms on fishery ecosystem productivity are largely unknown. I hypothesized these harmful algal blooms (HABs) would negatively impact walleye recruitment in a trophic cascade framework by altering algal community species and size composition, limiting suitable food particles available to zooplankton and therefore decreasing zooplankton abundance and causing a shift in community composition. This would directly impact the prey resources available to larval fishes during critical life stages, affecting their growth, survival, and recruitment to the young-of-year (YOY) stage. I investigated the potential for Lake Erie HABs to impact YOY forage fish availability and walleye year class strength using fisheries-independent data from the annual western basin interagency bottom trawl survey and satellite-derived estimates of HAB severity for 2002-2014. I further assessed how HABs impact zooplankton and ichthyoplankton prey availability by sampling Microcystis, zooplankton, and larval fishes in the western basin in 2015 and 2016. HABs did not have a significant impact on walleye year class strength, but they did impact the distribution of YOY and larval fishes in the western basin, in particular clupeid species. However, HABs were associated with increased zooplankton production, suggesting HABs directly impact larval and planktivorous fishes, rather than indirectly decreasing their abundance by limiting the availability of zooplankton prey.
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