Isotope and Diets for Perch and Goby Suggest Site-Specific Diet Specialization in Saginaw Bay

Many fish species, including yellow perch and round goby, display highly variable diet patterns, including spatial variation related to location-specific feeding patterns. Past analyses of yellow perch diets in Saginaw Bay, Lake Huron demonstrate consistent spatial differences in diet constituents. Such patterns may suggest that the Saginaw Bay food web is composed of spatially distinct sub-compartments. On the other hand, diet data are reflective of recent prey consumption and if individual fish move throughout the system, long-term diet variation among individuals may be negligible. Moreover, local prey specialization may not be consistent across species and life-stages. To evaluate site-specificity, we analyzed carbon, nitrogen, hydrogen and oxygen isotopes to look for long-term trends of fish residence. Our analysis of isotopes found that carbon and nitrogen differed significantly among sites. These isotopes are strongly related to diets of an individual and support our hypothesis of site-specific feeding fidelity. We often view aquatic systems to have homogenous fish populations, however our recent work supports the prevalence of smaller, separated sub-groups. This could have implications for management of Great Lakes fish, which most often occurs within a larger regional management unit.