Historical changes in abundance and community structure of warmwater piscivore communities associated with changes in water clarity, nutrients, and temperature

Abstract

In this study, we assess changes in the piscivore community of four large, shallow lakes in the Kawartha Lakes region of central Ontario, Canada, over the period from 1980 to 2003 and relate these changes to temporal trends in phosphorus concentration, water clarity, and temperature. Over the 24-year period of data collection, there has been a regional-scale decline in the relative abundance of walleye (Sander vitreus) and an increase in the relative abundance of bass (Micropterus spp.) species. These changes were associated with reductions in phosphorus concentration and increases in water clarity and summer temperature. Results of a comparative field study conducted on 13 regional lakes indicate significant positive associations between concentrations of total phosphorus and chlorophyll a and zooplankton and walleye density. These data suggest that bottom-up effects are limiting walleye abundance either directly or in combination with abiotic conditions that favour bass over walleye.