Physical and Biological Variables Useful for Predicting Population Characteristics of Smallmouth Bass and Rock Bass in an Ozark Stream

Abstract

Population characteristics of smallmouth bass (Micropterus dolomieui) and rock bass (Ambloplites rupestris) in Jacks Fork River, Missouri, were predicted from habitat and biological variables. We measured 32 variables at 20 sites that we believed might affect fish populations, and used multiple regression analysis to investigate relations between these variables and biomass, density, relative weight (Wr, an index of fish condition), and proportional stock density (PSD, an index of population size structure). Variability in density and biomass of both species was best associated with amounts of large substrate (boulders and cobble), undercut banks, and aquatic vegetation. Variability in Wr for both species was best explained by water temperature and the density of crayfish. Equations for both species were applied with satisfactory accuracy and precision to an independent data set. Variability in PSD was best explained by the presence of woody structure, aquatic vegetation, and large boulders; however, these equations were less satisfactory when tested on the independent data set. Management uses could include facilitating a stream inventory, estimating fish loss due to habitat modifications, and optimizing habitat improvement efforts.