An analysis of the influence of annual thermal variables on the occurrenceof fifteen warmwater fishes

Multisource fish-sampling data and U.S. Geological Survey temperature data from streams throughout the United States were used to investigate the infl uence of derived thermal regime variables on the presence or absence of 15 common warmwater fish species. The 3-year average annual thermal regime was calculated for streams where presence or absence was known for these 15 sp ecies. Six variables estimated to be of biological importance to the winter and summer survival and recruitment of a species, including measures of fe eding and nonfeeding periods, were calculated from these thermal regimes. S tepwise discriminant analysis and multiple regression were used to select o ptimal variables for creating multivariate models. Parametric and nonparame tric multivariate discriminant analyses were then performed to test our abi lity to correctly classify presence or absence using the thermal variables. These statistical empirical models were able to correctly predict presence or absence with greater than 90% accuracy for 13 of 15 species. Nonparamet ric (Kth nearest neighbor) analyses had marginally more accurate prediction s than parametric (linear) analyses. This technique may allow for an improv ed estimation of potential changes in distribution under various global war ming scenarios.