Relationship of fish catch and composition to water quality in a suite of agriculturally eutrophic lakes

We examined the fish community, water quality, and morphometry of 32 agriculturally eutrophic lakes. Our purpose was to explore the relationships between eutrophication and fish catch per unit effort by weight (CPUE _w) and fish community composition of the six most important species in this suite of the world's most nutrient-rich lakes. We found that the CPUE_w of the sum of all species increased with lake trophic status measured as chlorophyll a (r = 0.45, p < 0.009). By dissecting total fish CPUE_w into individual species and functional groups, we found that only common carp (Cyprinus carpio) and benthivore CPUE_w increased significantly with trophic status (p < 0.03 and 0.001, respectively). Sport fish (principally piscivores) decreased as a proportion of total CPUE _w by approximately 50%, while benthivores, primarily common carp, increased by approximately 80% over an increase in cholorophyll a from 10 to 100 μg·L^-1. Common carp CPUE_w was correlated with and may have a negative influence on CPUE_w of bluegill (Lepomis macrochirus) and black crappie (Pomoxis nigromaculatus) and a positive influence on white crappie (Pomoxis annularis). Our study suggests that species other than benthivores may be unable to exploit increased energy availability in hypereutrophic systems or are competitively excluded from using this increased production.