The Relationship between Aquatic Macrophytes and Sport Fish Production in Illinois Ponds: A Simple Model

Abstract

A model based upon simple assumptions about pond trophic dynamics was developed and used to examine the effects of various levels of plant control on sport fish populations. The model predicts a parabolic relationship between plant standing crops (mean concentrations) during the growing season in grams/m 3 and largemouth bass (Micropterus salmoides) production, implying the existence of an optimal target for macrophyte control efforts. Field data from experimental ponds were used to estimate model coefficients. As predicted by the model, invertebrate production and the production of insectivorous forage fishes were positively correlated with macrophyte population size, while piscivorous largemouth bass production was reduced at both high and low weed concentrations. Preliminary fits of the yield equation for largemouth bass gave an optimal macrophyte standing crop of 52 grams dry weight/m 3 for small ponds in central Illinois dominated by Potamogeton crispus and Najas flexilis.