Characteristics of fish assemblages and related environmental variables for streams of the upper Snake River basin, Idaho and western Wyoming, 1993-95

Fish assemblages and environmental variables
were evaluated for 30 first- through seventh-order
streams in the upper Snake River Basin,
Idaho and western Wyoming. Data were collected
as part of the National Water-Quality Assessment
Program to characterize aquatic biota and associated
habitats in surface water. Sampling sites represented
major stream types in the basin large
river, agricultural, and least-disturbed reference
streams and springs in forested and (or) rangeland
watersheds.

Twenty-four environmental variables representing
various spatial scales, from watershed
characteristics to instream habitat and physicochemical
measures, were used to examine relations
with fish assemblages. Twenty-six fish species in
the families Catostomidae, Centrarchidae, Cottidae,
Cyprinidae, Ictaluridae, Percidae, and Salmonidae
were collected. Detrended correspondence
analysis and canonical correspondence analysis
differentiated fish assemblages on the basis of site
type and showed that fish assemblages were most
strongly correlated with percent agricultural and
forest land uses, stream width, watershed size, and
elevation. Fish assemblages did not correspond to
the four major ecoregions in the basin. Comparisons
between multiple-year and multiple-reach
collections using Jaccard's coefficient of community
similarity index generally indicated little difference
in fish assemblages. Percent substrate fines,
percent embeddedness, and specific conductance
typically were higher for streams influenced by
agricultural land use than for reference streams in
forested and (or) rangeland watersheds. The number
of native species, percent introduced species,
percent omnivores, percent common carp, percent
salmonids, and percent coldwater-adapted species
varied according to site type. Percent omnivores
and percent common carp were higher for large
river and agricultural sites than for reference
stream and spring sites. The introduction of intolerant
salmonid species throughout the basin confounds
the use of introduced species as a measure
of environmental disturbance.

Analysis offish metrics identified some large
river and agricultural sites in the lower part of the
basin that did not support viable coldwater fish
assemblages. These sites characteristically were
dominated by tolerant, warmwater-adapted species.
The findings of this study support the waterquality-
limited designation for the middle reach of
the Snake River between Milner Dam and King
Hill and provide a framework for developing indices
of biotic integrity by using fish assemblages to
evaluate water quality of streams in the upper
Snake River Basin.