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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early sieve netting when icing of the net might be minimal, could add
some valuable data to determine transport of overwintered kokanee.

Based on our preliminary findings and information from other sources,
fish losses appear to have less of an impact on the reservoir fishery
than possibly other factors such as actual harvest or predation. This
is not to say that significant losses couldn't occur in winter or
early spring, or under different operational and physical reservoir
conditions (i.e., surface spills or lower reservoir elevations).
Further monitoring and study are needed.

Fish Behavior and Facility Operational Considerations

Sieve netting below the powerplant indicated that the majority (96%)
of fish leaving the reservoir were small (30-120 mm) kokanee salmon.
This suggests that actual impacts to the creel may be delayed,
possibly as long as 2-3 years, the time necessary for these young fish
to reach harvestable size (CDOW reference). If the 1994 and 1995
harvest declines did occur due to higher spring releases, young
kokanee would have had to have been transported in 1992 and 1993.

Hydroacoustic technology provides a valuable tool for measuring and
describing a pelagic fishery. Like all sampling techniques it
possesses specific strengths and weakness that need to be recognized
when reviewing the data. For instance, we 1I1ooked atll tens of
thousands of fish during the four field trips measuring actual fish
density (fish/mJ) and gathering information and relative fish size.
This simply would not be practical using conventional sampling
techniques. Also, fish found within the sound beam cannot evade
detection. Recent studies comparing acoustical and trawling
techniques showed that population estimates derived from acoustical
systems were typically 1.8 to 3.3 times greater than those calculated
from trawling data (Parkinson et al. 1994). Lower trawling estimates
were attributed to fish avoidance.

However, this technology does exhibit some "blind" spots. Fish found
within the littoral zone (<10 m), those found within 1.5 m of the
surface, 1 m of the bottom, or near submerged cover are not detected.
We are confident that adult kokanee population estimates accurately
describe those fish found in pelagic habitats at depths greater than
1.5 meters.

During August surveys, we observed large numbers of small kokanee
feeding near the surface where the zooplankton were swarming. Young
of the year kokanee can tolerate warmer temperatures than their adult
life stages. Fast growth during their first year must be attributed

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