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

I

I

I

I

I

I

I

I

I

I
I

I

I

I

I
I
I

I

I

on.2 Hl7

~elagic fish population estimates were calculated by two methods. One
method used the average fish density developed for the entire
reservoir while the second used average values produced for each
separate basin. These estimates were based on the following data or
assumptions:

. Fish were not randomly distributed throughout the reservoir, a
statistical analysis of survey means rather than transect averages
were most appropriate,

. Vertical gill netting data of kokanee (96% measured) represents an
accurate representation and proportion of the pelagic fish community
(Johnson et al. 1995).

Surface elevation of Blue Mesa reservoir during June, August, and
October 1994, was 2,289, 2,287, and 2,284 m respectively and 2,290 m
in 1995. The majority of fish were found at a depth between 20 and
35 m. We therefore, adjust the surface area to reflect the area used
by fish community to calculate units of fish per surface area
(fish/ha). Since the elevation range was similar, we chose to use
August's elevation to simplify calculations (2,287-20=2,267 m). The
surface area of elevation 2,267 m is 2,028 ha (5,010 acres) based on
existing area-capacity information (Bureau of Reclamation,1975).
Reservoir elevation in 1995 was higher, at 2,290 m, or a surface
elevation of 2,258 ha (5,580 acres).

Surveys (Figures 9, 10, 11 & 12)suggested that fish distribution was
not random, but sKewed or contagious, making it inappropriate to test
the variance of individual transect densities. However, we can set
confidence limits for the two data sets collected in both August and
October 1994.

The average fish density measured in the June 1994, survey was
485 fish/ha. Based on 2,028 hectares the reservoir's pelagic fish
population is estimated at 983,580 fish (Table 5). During the two
August fish surveys, average pelagic fish densities were measured at
344.3 and 329.8 fish/ha with an average of 337 fish/ha (STD=7.63).
using a Student's T analysis and a 90 percent confidence interval
(a=.10) the average fish density of Blue Mesa Reservoir was 337 ~ 48
fish/ha. The reservoirs pelagic fish population was estimated (337 ~
48 fish/ha X 2,028 ha) at approximately 683,436 ( ~ 97,344) fish,
based on a surface area of 2,028 ha. It's estimated with 90 percent
confidence the pelagic fishery is somewhere between 586,092 and
780,780 fish. October's estimate was 263,600 fish with a range of
14,200 to 513,100. The average density in 1995 was 201 fish/ha.
Estimated kokanee population for 1995 based on 2,258 surface hectares
was 454,000 fish.

23