Recent Invasive Species Induced Changes to the Saginaw Bay Food Web: Insights from Bioenergetics Analyses

Saginaw Bay, Lake Huron, has historically supported economically important commercial and recreational fisheries for numerous species, including walleye and yellow perch.  However, over the past 15 years Saginaw Bay’s ecosystem has been altered by a series of dramatic shifts among key invasive species, which have in turn impacted native fish stocks and their associated fisheries.  Alewives, until recently the dominant planktivore in Lake Huron, have collapsed; dreissenid mussels have declined, with quagga mussels (Dreissena bugensis) replacing the previously dominant zebra mussels (D. polymorpha); round gobies have increased in abundance; and the predatory zooplankton, Bythotrephes longimanus, has seemingly proliferated.  Coincident with, or perhaps in response to, these changes among invasive species, dynamics of Saginaw Bay percid populations have shifted.  Walleye, previously supported through stocking, now successfully recruit naturally, and a relatively large walleye population supports a thriving recreational fishery.  In contrast, while yellow perch also enjoy high early-life survival, young perch experience poor growth and are recruiting to the adult population with limited success, leading to reduced adult population size and poor catch rates.  We use a series of bioenergetics-based models to elucidate the mechanisms and consequences of these recent alterations to the Saginaw Bay ecosystem.  We couple contemporary measures of walleye, yellow perch and round goby diets in Saginaw Bay with bioenergetics models to evaluate potential top-down impacts on lower trophic levels and consequences for fish growth.  In addition, we use a 3-dimensional water quality model to drive a spatially-explicit individual-based model of walleye and yellow perch and evaluate how various ecosystem changes may impact percid growth, recruitment success and subsequent population abundance.   Collectively, these analyses demonstrate how changes among invasive species have had dramatic impacts on multiple components of the Saginaw Bay food web.  The restructuring of the Saginaw Bay food web is likely an on-going phenomenon that may not reach fruition before the next dramatic change to the bay’s ecosystem.