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The objective of the NAWQA characterization of fish community structure is to relate fish community characteristics to physical, chemical, and other biological factors as part of an integrated assessment of the Nation's water-quality conditions. To accomplish this, fish community structure is described at sites representing selected environmental settings. In addition, spatial and temporal patterns in fish community structure are examined at local, regional, and national levels. An integrated assessment of water quality will provide information to address questions, such as:

1. What are the relations among fish community structure, benthic invertebrate community structure, algal community structure, physical habitat complexity, and water chemistry under varying environmental settings?
2. How do local natural and human factors influence these relations--for example, what is the influence of local agricultural practices on the relations of fish community structure, benthic invertebrate community structure, algal community structure, physical habitat complexity, and water chemistry?
3. What is the influence of regional characteristics on these relations?
4. What patterns exist in the relations among temporal changes in fish community structure, physical habitat complexity, and water chemistry?

An integrated database will also provide information to generate additional hypotheses and address specific questions at local, regional, and national levels.

Purpose and Scope

This document provides detailed procedures for use by trained biologists in evaluating stream fish communities as part of the U.S. Geological Survey's (USGS) NAWQA Program. These procedures allow standardization of collection methods and descriptions of fish communities to facilitate unbiased evaluations of relations among physical, chemical, and biological components of water-quality conditions. The methods presented in this document have been established as standard procedures for characterizing fish communities in streams ranging from headwaters to large rivers (Bagenal, 1978; Nielsen and Johnson, 1983; Bryan, 1984; Ohio Environmental Protection Agency, 1987; Britton and Greeson, 1988; and Plafkin and others, 1989).

This document describes the sampling approach to be used in characterizing fish communities. This approach considers availability of existing data, the selection of sampling sites, the sampling reach, and the sampling season.

Sampling procedures focus mainly on electrofishing and seining techniques, but other sampling methods are discussed. Sampling-related issues include collection of permits, concerns about endangered species, and coordination of activities with other ecologists.

The processing of samples covers taxonomic identification, physical measurements, examination of fish for external anomalies, and the preservation of specimens. Forms for recording these data are presented.