Tr. Maret et al., FISH ASSEMBLAGES AND ENVIRONMENTAL CORRELATES IN LEAST-DISTURBED STREAMS OF THE UPPER SNAKE RIVER BASIN, Transactions of the American Fisheries Society, 126(2), 1997, pp. 200-216
Fish assemblages and environmental variables were evaluated from 37 le
ast-disturbed, 1st- through 6th-order streams and springs in the upper
Snake River basin, western USA. Data were collected as part of the ef
forts by the U.S. Geological Survey National Water Quality Assessment
Program and the Idaho State University Stream Ecology Center to charac
terize aquatic biota and associated habitats in least-disturbed coldwa
ter streams. Geographically, the basin comprises four ecoregions. Envi
ronmental variables constituting various spatial scales, from watershe
d characteristics to instream habitat measures, were used to examine d
istribution patterns in fish assemblages. Nineteen fish species in the
families Salmonidae, Cottidae, Cyprinidae, and Catostomidae were coll
ected. Multivariate analyses showed high overlap in stream fish assemb
lages among the ecoregions. Major environmental factors determining sp
ecies distributions in the basin were stream gradient, watershed size,
conductivity, and percentage of the watershed covered by forest. Lowl
and streams (below 1,600 m in elevation), located mostly in the Snake
River Basin/High Desert ecoregion, displayed different fish assemblage
s than upland streams (above 2,000 m elevation) in the Northern Rockie
s, Middle Rockies, and Northern Basin and Range ecoregions. For exampl
e, cottids were not found in streams above 2,000 m in elevation. In ad
dition, distinct fish assemblages were found in tributaries upstream a
nd downstream from the large waterfall, Shoshone Falls, on the Snake R
iver. Fish metrics explaining most of the variation among sites includ
ed the total number of species, number of native species, number of sa
lmonid species, percent introduced species, percent cottids, and perce
nt salmonids. Springs also exhibited different habitat conditions and
fish assemblages than streams. The data suggest that the evolutionary
consequences of geographic features and fish species introductions tra
nscend the importance of ecoregion boundaries on fish distributions in
the upper Snake River basin.