Using Models to Evaluate Predator/Prey Balance (or imbalance) In the Great Lakes Ecosystems

Great Lakes ecosystems are stressed at multiple trophic levels.  Some key recreational fisheries (i.e., Chinook salmon in Lake Huron) have experienced dramatic declines in recent years, and prey fish populations in several systems are declining to levels of biomass not observed in the past 30 years.  Recent surveys of lower trophic levels have revealed marked changes in zooplankton community composition and declines in spring phytoplankton densities.  Possible mechanisms to explain these changes include excessive consumption by piscivores (Chinook salmon), invertebrate planktivores (Bythotrephes) or invertebrate herbivores (dreissenid mussels) as well as “bottom-up” driven-changes wrought by declines in phosphorous loading.  Models that incorporate trophic dynamics allow some of these mechanisms to be evaluated.  Speakers in this symposium will use these models with the goal of providing an ecosystem perspective to fishery managers to explain some of the recent ecosystem changes that may have affected or will affect Great Lakes fisheries.  Because ecosystem-based fishery management is being increasingly advocated among fishery managers and scientists across the world, the modeling approaches discussed in this symposium will have broad application beyond the Great Lakes region.