FIGURES

   1. Map showing location of study sites, ecological regions, and TWINSPAN site groups

2-4. Graphs showing:

2. Principal component analysis plot of site scores on the first two principal components derived from the environmental variables for sampling sites in the Sacramento River Basin, California

3. Plot of scores on the first two axes from the canonical correspondence analysis for sampling sites in the Sacramento River Basin, California

4. Plot of detrended correspondence analysis site scores derived from fish species percentage-abundance data from sampling site in the Sacramento River Basin, California

TABLES

1. Site name, site code, and year(s) sampled for study sites in the Sacramento River Basin, California

2. Common name, species code, scientific name, origin, species group, trophic group, tolerance,and percentage of fish caught in each TWINSPAN site group for all species captured in the Sacramento River Bsin, California

3. Principal component loadings for habitat and water-quality variables from principal component analysis of physical data from 14 of the 22 sites sampled in the Sacramento River Basin, California

4. Mean and range of selected water-quality and habitat variables for the four site groups resulting from TWINSPAN analysis of fish species percentage abundance in the Sacramento River Basin, California

5. Results of canonical correspondence analysis relating fish percentage abundance data to environmental variables in the Sacramento River Basin, California

6. Median and range of selected fish community metrics for TWINSPAN site groups in the Sacramento River Basin, California

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.

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For additional information          Copies of this report can be 
write to:                           purcahsed from:

District Chief                      U.S. Geological Survey
U.S. Geological Survey              Information Service
Placer Hall, Suite 2012             Box 25286
6000 J Street                       Federal Center
Sacramento, CA 95819                Denver, CO 80225

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