Size and species selection of zooplankton by larval and juvenile walleye (Stizostedion vitreum vitreum) in Oneida Lake, New York

Abstract

Young-of-the-year walleye (Stizostedion vitreum vitreum) ranging from 7 to 38 mm in total length were collected from Oneida Lake, New York, from 14 May to 11 June, 1989. Stomach contents were analyzed to document feeding strategies employed during their early life stages. A distinct change in both type and size of prey was evident as the walleye progressed through their first 4 weeks of life. The diet of 10- to 13-mm walleye consisted of 77.3% (by number) cyclopoid copepods; walleye 13–19 mm in total length consumed calanoid copepods (96.1%), while the diet of older juveniles, 29–38 mm in total length, consisted of mostly cladocerans (Daphnia spp.) (88.3%). The smallest size class of fish consumed zooplankton 0.50–1.50 mm long, the second class of fish consumed 1.25- to 2.00-mm zooplankton, and the third class consumed 1.5- to 2.00-mm zooplankton. Electivity calculations from both field and laboratory studies revealed that these changes were a result of active selection by the young walleye. The smallest walleye consumed zooplankton as large as their mouth gapes would allow. As the larvae increased in size they began to consume zooplankton of intermediate size (mouth gape approximately 2.0 mm) and remained consistent in their choice thereafter. We suggest that young-of-the-year walleye foraged in a manner that optimized growth. Both species and size of zooplankton were important components of their feeding strategy.