Habitat associations of fish assemblages in the Sulphur River, Texas

Abstract

As part of an instream flow study, information on summer distribution of fishes and habitat variables was collected from six sites at each of three flows in the Sulphur River, Texas. I evaluated (1) spatiotemporal relationships between instream habitat features and fish assemblage structure, (2) variation in fish assemblage structure explained by combinations of hydraulic and structural instream habitat features at three levels of habitat aggregation (coarse, intermediate, fine), and (3) the potential to accurately describe summer habitat associations for fishes in southern prairie rivers. Most fishes occurred in a variety of habitats in the Sulphur River and did not reveal discrete habitat associations. The range of explained variance was relatively low for relationships among species and habitat variables across three levels of habitat aggregation. Variation in fish assemblage structure explained by habitat changed from 24, to 30, and to 36 percent as the level of aggregation changed from coarse, to intermediate, and to fine. After accounting for the variance explained by hydraulic variables, the remaining variance explained by structural habitat variables was 7.2% for the coarse aggregation, 13.2% for the intermediate aggregation, and 19.3% for the fine aggregation. In this river, where pools were predominant, microhabitat variables independently explained greater variance in species distribution (6.1%) than did mesohabitat (3.7%) or location (2.3%) variables at the intermediate aggregation level. The ability to describe summer habitat associations for fishes in southern prairie rivers, such as the Sulphur River, is complicated by poor stream access and by problems posed by gear-related biases in sampling a variety of instream habitat types. Identifying appropriate habitat criteria for instream flow studies on the Sulphur River poses a challenge due to the abundance of habitat generalists in this system.