WSP05499

• File Number: 8200.766
• Description: Gunnison River General
• State: CO
• Basin: Gunnison
• Water Division: 4
• Date: 4/1/1997
• Author: Mueller and Hiebert
• Title: Assessment of Kokanee Salmon Transport through Blue Mesa Powerplant - Colorado - During the Spring and Summer of 1994-1996
• Water Supply Pro - Doc Type: Report/Study

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the fish were found at depths >30 m at night while >30 percent of
the fish were detected at depths greater than that during day
light. From the distribution and passage information, it appears
that during the day, fish migrate to deeper depths which might
make them more susceptible to entrainment or passage. Fish
abundance during daylight hours increased at depths where the
highest (15 cm/s) intake velocities were measured near the dam.

Early in the spring, fish were generally found in the deeper
reservoir basins. Fish became more widely dispersed as the
reservoir warmed and with the release of kokanee from the Roaring
Judy Hatchery. The highest fish densities were found at the
upstream portion of the reservoir. By midsummer, the reservoir
became more stratified and thermally sensitive adults were again
restricted to the deeper and cooler portions of the reservoir. As
the reservoir cooled again in early fall, adult kokanee moved
into shallower, inflow or riverain habitat to spawn.

Population estimates declined through the summer as would be
expected. June estimates represented a mixture of young and
adult fish that were disbursed throughout much of the water
column. By August, adults were thermally restricted to the
deeper depths of the reservoir, which made it much easier to
detect larger kokanee from other fishes. This stratification of
the fishery allowed us to more accurately predict the kokanee
population at roughly 683,000 (z 15%)fish in 1994 and 454,000 in
1995. Population levels in 1995 were well below (-34%) 1994
estimates.

A similar decline (-31%) was reported for kokanee harvested
between 1994 and 1995. The decline is more dramatic if one goes
back to 1993 when 225,000 kokanee were harvested. Anglers
harvested 39 percent less kokanee in 1994 and 59 percent less in
1995 compared to 1993 levels. Similar declines were witnessed
for the rainbow trout fishery. Nearly 63,000 rainbow trout were
harvested in 1993 compared to only 35,000 in 1995. While these
declines appear large, they are largely influenced by angler
effort which dropped by nearly 50 percent over this 3-year
period. Angling success rates, the number of fish caught per
fisherman trip, did decline, but only by 6 percent
2.69-2.52 fish/trip). The reservoir fishery may have declined,
but not as dramatic as the harvest numbers would suggest.

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