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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Reservoir Fishery

In 1993, CDOW voiced concern over the possible loss of kokanee through
higher spring and summer releases. It's believed their assumption was
that increased releases would result in increased losses of kokanee
salmon. ereel census data collected during the past three years has
indeed shown that harvest rates have declined nearly 59 percent. More
than 255,000 kokanee were harvested in 1993 compared to only 105,000
in 1995. During this period stocking rates from Roaring Judy Hatchery
have actually increased from roughly 1.4 to 1.6 million kokanee each
year.

Declines in the number of kokanee harvested (-34%) also mimicked the
population estimates developed from our hydroacoustic measurements
(-31%) which probably provide the most accurate data regarding adult
kokanee. Similar, surveys done by CDOW showed comparable declines
(Pat Martinez eDOW personal communique). Actually, limnological
conditions combined with the thermal sensitivity of this life stage
made conditions ideal to survey and calculate the harvestable portion
of the population. Based on our calculations, the adult kokanee
population of Blue Mesa Reservoir was between 586,000 and 780,000 fish
in 1994 (August). This corresponds with CDOW's estimate of 746,895
kokanee (Martinez 1995). Estimates for 1995 were slightly lower at
around 454,000 fish. These estimates represent the total pelagic
fishery_ Kokanee salmon represented 97 percent of the pelagic fish
community based on vertical gill netting conducted in August 1994
(Johnson et al. 1995). It appears that the rainbow trout fishery also
dropped (Sherman Hebein eDOw, unpublished data), from nearly 63,000
rainbow trout harvested in 1993 compared to only 35,000 in 1995.

While these harvest 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). Angler success rates (epUE) are normally regarded as a
more accurate indicator of the fish abundance (Hubert 1983) .

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