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ISMP backwater sampling evaluation <br />Fish community and habitat relationships <br />We also explored the relationship between biotic and physical habitat variables and the <br />presence and abundance of green sunfish, largemouth bass, and the three non-native cyprinids. <br />Probability of fish presence as a function of four habitat variables, backwater area, mean depth, <br />maximum depth, the qualitative index of habitat complexity, and the year effect, was explored <br />with a binomial regression model with a logit link function. Abundance (density) of green <br />sunfish, largemouth bass, and the three non-native cyprinids as a function of four habitat <br />variables was explored with a general linear model (GLM). Backwater areal, mean depth, <br />maximum depth, and a qualitative index of habitat complexity were the independent variables in <br />the analysis. Because fish abundance data are divided by backwater surface area to yield fish <br />density, the backwater area covariate is expressed as a squared term to avoid confounding. The <br />response variable, estimated fish density (fish/lOm2), was transformed as log (x + 1). In models <br />that predicted non-native cyprinid density, predator density (the sum of the green sunfish and <br />largemouth bass densities in each backwater) was used as an additional covariate. <br />We also assessed the relationship between fish species richness in backwaters as a <br />function of four habitat variables, backwater area, mean depth, maximum depth, the qualitative <br />index of habitat complexity. A GLM that assumed a normal error distribution was used. We <br />also included river kilometer to determine if spatial location affected fish species richness in <br />backwaters. For the purpose of this analysis, a composite estimate of backwater species richness <br />was generated from the results of ISMP and DMR sampling. <br />We also plotted density estimates of the two centrarchids and three non-native cyprinids <br />obtained during 1986 to 1999 during the regular ISMP sampling that was conducted by other <br />-8-