WWRC 85-15
Winter Stream Conditions and Brook Trout Habitat Use
on the Snowy Range, Wyoming
Abstract
As demand for water increases in Wyoming, water diversion from high
mountain areas is being considered more often. Instream flow assessment
methods are based on summer and fall flows, but low base-flows extend into
winter. Little is known of winter conditions in high mountain streams or the
instream flow requirements during winter. The objectives of this study were:
(1) to describe winter habitat conditions on streams at elevations above 8,000
feet, (2) to determine the effect of decreasing elevation on the amount of
potential habitat excluded by ice, (3) to verify brook trout use of stream
habitats at elevations above 8,000 feet, and (4) to determine brook trout
winter habitat associations in such streams.
Above 9,000 feet, snow insulated the study streams and habitat exclusion
by ice was minimal. As elevation decreased, snow depths increased and ice
formation increased. Ice depths and the amount of ice-excluded habitat were
greatest at the lowest study site (7,500 feet). Stream conditions were
harshest and most variable at mid-elevation sites (8,300-8,800 feet) where the
streams were partially ice and snow covered and subject to anchor ice
formation.
Brook trout remained active in streams above 9,800 feet throughout the
winter. Current velocity was the most important variable governing habitat
selection of adult brook trout with the fish showing preference for areas with
a mid-stream velocity of less than 6 inches/second. Water depth and substrate
did not appear to influence trout distribution under deep snow. Flowing water
is needed during winter in high mountain streams for incubating trout eggs,
enabling young-of-year trout survival and preserving stream invertebrate
production.
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