Lack of a unimodal relationship between fish growth and macrophyte cover in 45 north temperate lakes

Abstract

Macrophytes have several important roles for fish populations in lakes. Theory and experimental evidence support the hypothesis of an optimal intermediate macrophyte cover for fish foraging and growth. However, few multi-lake studies of this relationship have been conducted at the whole-lake scale in north temperate lakes, and results to date have not been consistent. We examined the relationship between macrophyte cover and fish growth for two fish species that are tightly linked to macrophytes, largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus). We conducted our study on 45 thermally stratified north-temperate lakes using nine macrophyte cover metrics at both the whole-lake and littoral-zone scales. We found little evidence to support the hypothesis of an optimal intermediate range of any macrophyte cover metric for fish growth. However, growth for some ages of both species was negatively related to some of the macrophyte metrics at each spatial scale. These results should help direct more holistic management of lakes by informing the management of both macrophytes and fish, and serve as a caution to ecologists and managers attempting to extrapolate theoretical and experimental results to the whole-lake scale.