Effects of Productivity Gradients on Fish-Community Structure in Lake Erie

Lake Erie has strong productivity gradients caused by nutrient distribution which may affect trophic levels. This study was designed to quantify how multiple productivity gradients affect energy flow to fish and the resulting fish-community structure. Water quality, zooplankton, benthos, and fish data were collected across several gradients in 2014; west to east, near-shore to offshore, and seasonal. We used classification and regression trees (CARTs) to determine which factors most influence total fish biomass and percent percid biomass (an indicator of desirable fish community). Region explains the majority of variance in total biomass whereas benthic and pelagic food web structure explains the majority of variance in percent percid biomass. This suggests overall productivity determines total fish biomass but biotic factors such as food availability determine composition. Informed by the CARTs we constructed a series of regression models (e.g. phosphorus-chlorophyll, chlorophyll-zooplankton biomass). These relationships were connected by a Bayesian network model. A positive relationship exists between productivity and fish abundance and a negative relationship exists between benthic biomass and percent percid biomass. However, the strength of the relationships varies with location along productivity gradients. This suggests that different management strategies would be needed depending on the location and desired fish community.