Effects of Zooplankton Density on Survival of Stocked Walleye Fry in Five Pennsylvania Reservoirs

Abstract

ABSTRACT Over the past several years, management agencies in the United States have stocked billions of larval walleyes to augment natural reproduction, yet success of these programs has generally been limited by poor first-year survival. We conducted a two-year field study of five impoundments in western and central Pennsylvania to determine if seasonal zooplankton density was related to first year survival of stocked walleye larvae. Using sampling methods that could be easily replicated by state fisheries management agencies, we assessed the magnitude and timing of spring zooplankton blooms in relation to first-year survival of stocked walleye larvae. Our findings showed that although zooplankton production may vary widely among study waters and across years, fry survival was highest when the combined density of large-bodied clasdocerans and adult copepods exceeded 100 organisms/L. When peak zooplankton densities were less than 100/L, few walleye fry survived.