Biomass Model of Reservoir Fish and Fish-food Interactions, with Implications for Management

Abstract

A mathematical model was developed to help evaluate trophic relations of fishes in reservoirs and to assess the effects of perturbations (e.g., reservoir operations, species introductions, stocking, and harvest) on reservoir ecosystems. The model estimates the production and food requirements of five functional groups of fish biomass, established according to the food supporting each group-(1) plants and detritus, (2) benthos, (3) zooplankton, (4) fish, and (5) terrestrial invertebrates. When applied to data collected from 1977 to 1980 in DeGray Lake, Arkansas, the model revealed that the biomass of fish supported by diets of plants and detritus (BSPD) was positively correlated with precipitation within and among years. The BSPD, expressed as a percent of the total standing crop, declined significantly from 1974 to 1977 and then stabilized at a low level from 1977 to 1980. In 1979, primary production was insufficient to sustain zooplankton production and BSPD from June to mid-August, and from late September to early October. The mean monthly biomass of benthos, estimated from food requirements of benthophagous fish, was within the range of published weights. Production of zooplanktivorous fish was limited by declining zooplankton production in late summer, and piscivore production was limited by the availability of prey fish in early spring and late summer.