Abstract

Twenty-two sites in the Sacramento River Basin, California, were sampled from 1996 to 1998 to characterize fish communities and their relation to water quality and habitat quality. The feasibility of developing an Index of Biotic Integrity (IBI) for the study area was assessed by evaluating six fish community metrics, including percentage of native fish, number of native species, percentage of intolerant fish, number of tolerant species, percentage of omnivorous fish, and percentage of fish with external anomalies. Of the 36 taxa of fish captured during the study, only 13 taxa were native to the drainage. Multivariate analyses identified four site groups that were characterized by four species groups. The distributions of fish species were correlated with elevation of a sampling site and substrate size; however, elevation was correlated with a suite of water-quality and habitat variables. Four of the fish community metrics—percentage of native fish, percentage of intolerant fish, number of tolerant species, and percentage of fish with external anomalies—were responsive to environmental quality. In contrast, number of native species and percentage of omnivorous fish were not correlated with environmental quality. Fish communities in the Sacramento River Basin appeared responsive to environmental gradients, and several of the metrics tested reflected these relations. These results suggest that IBI-type indices can be developed for the basin.