ONTOGENIC DIET SHIFT IN LAKE ERIE AGE-O YELLOW PERCH (PERCA-FLAVESCENS) - A SIZE-RELATED RESPONSE TO ZOOPLANKTON DENSITY

Through field studies, we demonstrated that age-0 yellow perch (Perca flavescens) in western Lake Erie underwent an ontogenetic diet shift from exclusively zooplankton to mainly benthic prey during June through August. This shift coincided with a decline in zooplankton populations in the lake. Further, laboratory experiments on feeding ontogeny suggest that the diet shift was related to fish size. Yellow perch less than 30 mm total length did not consume benthic prey either during the feeding experiments or in the field studies, while fish greater than 50 mm did at low zooplankton densities. Interactions between fish size and zooplankton density, therefore, likely determine the ontogenetic diet shift in young-of-the-year yellow perch. Growth of yellow perch declined following the zooplankton decline. Reduced growth during this life stage may extend the period of vulnerability of yellow perch to its predators, thus reducing survival and, ultimately, recruitment.