Condition and diet of yellow perch in Saginaw Bay, Lake Huron (1970-2011)

In Saginaw Bay, Lake Huron, yellow perch (Perca flavescens) constitute an ecologically important component of the ecosystem and support both recreational and commercial fisheries. Over the past 40 years, Saginaw Bay has experienced multiple ecosystem-level changes (e.g., non-indigenous species introductions, reduced nutrient loading and variable temperatures). In turn, abundances and growth rates of yellow perch and their predators and prey have fluctuated. Recent changes to Saginaw Bay and Lake Huron foodwebs have potential to influence prey composition and subsequently, growth and condition for yellow perch; but a complete description of yellow perch diet composition across seasons has not been undertaken in recent years. We calculated mean relative weight (Wr), an index of condition, of age-1 and older yellow perch in Saginaw Bay annually for 1970-2011. We found high interannual variation in condition and documented low mean Wr during 1978-1991. We developed regression models to explain this variation using phosphorus load, temperature, forage fish density, and yellow perch density as potential explanatory factors. Patterns of Wr were associated with changes in yellow perch densities, although interannual variation was not significantly associated with any of the available explanatory variables. Diet analysis of yellow perch collected in 2009 and 2010 demonstrated that age-1 and older yellow perch consumed a fundamentally different diet from a previous study (1986-1988), exhibiting a greater reliance on non-indigenous prey (e.g. Bythotrephes longimanus).