WWRC 87-11
Modified Habitat Suitability Index Model for Brown Trout in Southeastern Wyoming
Abstract
The habitat suitability index (HSI) model for brown trout Salmo trutta in stream
systems, developed by the U.S. Fish and Wildlife Service, was tested with data from 30 reaches
on nine streams in southeastern Wyoming. The HSI was not significantly correlated (P > 0.05)
with brown trout standing stock. We analyzed 14 individual suitability index variables from the
HSI model plus 25 other habitat variables for their relation to standing stock. Two HSI model
variables and seven of the additional variables had significant correlations with brown trout standing
stock. When these nine variables were used in multiple regression analysis, the best model (R2 =
0.52) for predicting standing stock (S. kg/hectare) of brown trout included measures of cover and
flow regime: 5 = 1.71MTCR + 114.3V14 - 0.60; MTCR is a measure of cover availability and
V14 is the average annual base flow expressed as a percent of average annual daily flow. An index
of fishing pressure was also developed and found to significantly influence brown trout standing
stock.
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