The relationship between an index of fish production and submerged macrophytes and other habitat features at three littoral areas in the Great Lakes

An index of fish production was significantly higher in littoral habitats with abundant submerged macrophytes, as measured by percent bottom cover, than in adjacent areas with low macrophyte abundance. Plots of fish abundance versus fish size showed that vegetated sites had higher densities of fish, smaller fish, and greater species richness than unvegetated sites. Using information on fish biomass (B) and fish size (W), a production index (PI) was calculated as log(10) PI = -0.35 log(10) W + 0.90 log(10) B. The production index was significantly related to macrophyte density, phosphorus, slope of the littoral area, and fish species richness. The regression model explained 61% of the variability in PI if species richness was included but only 43% if habitat features alone were used. Fish numbers decreased, and conversely fish size increased, with increasing littoral slope and maximum exposure. Species richness was correlated with effective fetch, but in a nonlinear manner. Methods for increasing the precision of models for estimating fish production in littoral habitats are suggested. Conservation should be directed at protecting not only the productive vegetated littoral habitats but also adjacent areas which benefit from the high productivity as well.