Effects of Changes in the Zooplankton Assemblage on Growth of Bloater and Implications for Recruitment Success

Abstract

Abstract Historical variation in the abundance of bloater Coregonus hoyi in Lake Michigan may have involved a link between growth rates of juvenile bloaters and the species and size distributions of zooplankton. These distributions have varied dramatically in response to fluctuations in abundance of alewife Alosa pseudoharengus. Bloater recruitment was poor from the mid1960s to the mid-1970s. If bloater growth rates were reduced when large zooplankton were rare, as in the mid-1960s, juvenile bloaters would have been exposed to size-dependent mortality sources longer and, hence, would have experienced poor survival. Two sets of experiments were used to test this hypothesis. First, we investigated changes in prey size selectivity during the ontogeny of bloater. Our experiments showed that the size of prey that elicited significant positive selectivities increased from 0.3 mm in 20-mm bloaters to 2.3 mm in 100-mm bloaters. These results were then used to predict the outcome of 30-d growth experiments involvi...