WWRC 91-17
Brown Trout Population & Habitat Response
to Enhanced Minimum Flow in Douglas Creek, Wyoming
Abstract
We assessed the biological significance of an increase in minimum
flow to brown trout (Salmo trutta) in Douglas Creek, Wyoming. Douglas
Creek is a regulated stream that underwent an increase in the required minimum
flow in 1986 to 5.5 ft3/second after 23 years of minimum flow at 1.0 ft3/second.
We compared population and habitat data obtained during the period when
minimum flow was 1.0 ft3/second (1972-1976) with data collected after the
minimum flow was 5.5 ft3/second (1988-1990). An increase in brown trout
standing stock in excess of natural fluctuation was observed at one site within
7.4 mi of Rob Roy Dam with more deep water for juvenile and adult fish at the
site. At a second site within 7.4 mi of Rob Roy Dam, the standing stock estimates
remained within the range of natural variation, but instream cover was probably
limiting at that site. There was no evidence of enhanced standing stocks at sites
more than 7.4 mi downstream from Rob Roy Dam where the effect of the low
minimum flow was reduced because of the addition of water from tributary
streams. The assumption that enhanced minimum instream flow for fisheries
should result in the production of more or larger fish was not supported at most
of the study sites in Douglas Creek.
KEY WORDS: Brown trout, diversion, habitat, instream flow, minimum low
flow.
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