9299

• UCREFRP Catalog Number: 9299
• Author: Anderson, R. and J. Mumma.
• Title: Aspinall Studies
• USFW Year: 1999.
• USFW - Doc Type: Annual assessment of Colorado Pikeminnow Larval Production in the Gunnison and Colorado Rivers, Colorado 1992-1996.
• Copyright Material: NO

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Table 6. Seasonal drift densities for Lorna, Westwater and Moab and coefficient of
determination (r) between the three sites, and summer, fall and spring
densities of Colorado pikeminnow YOY seined in backwaters and the r2
between drift and backwater densities, and over-winter survival estimates
based on spring and fall densities.

YEAR DRIFT DRIFT DRIFT SUMMER FALL SPRING OVERWINTER
LOMA WW MOAB Mean Mean Mean SURVIVAL
#/1000m3 #/1000m3 #/1000m3 #/100m3 #/100m3 #/100m3 Percent
1992 6.6 1.1 8.8 17.9 14.2 4.7 33%
1993 3.6 2.5 11.5 3.2 8.6 0.87 10%
1994 3 0.53 1.08 3.8 1.1 2.5 214%
1995 12.9 1.46 41.7 0.07 1.0 0.10 9%
1996 2.4 1.64 22.6 78.0 37.6 No Data No Data
LOMA r2 - 0.0022 0.5712 0.2049 0.2285
WWr2 - - 0.0815 0.0087 0.0559
MOAB r2 - - - 0.0094 0.0022
SUMM ~ - - - - 0.9521

Drift densities at Loma and Moab, separated by over 100 miles, were more closely
correlated (R2 = 0.57) than Loma-Westwater or Westwater-Moab (Table 6). The strength
of the Loma/Moab relationship was due to the highest drift densities for both sites
occurring in 1995. 1995 was the highest flow year, which suggests that high flows may
stimulate increased spawning efforts and larval production in those reaches. Drift
densities were third highest in 1993 at both sites. The low flow years (1992 and 1994)
ranked fourth and fifth, respectively at Moab and second and fourth, respectively at Loma.
The lowest drift density at Loma and the second highest drift density at Moab occurred in
1996, the intermediate flow year.

Catch rates in fish/1000m3 were substantially higher at Moab than at Westwater
for all years, and higher than Loma in four of the five years. Total transport abundance
was higher at Moab than at Lorna or Westwater for all five years, which suggests some
spawning taking place below Westwater.

Non Native Cyprinid - Catch Characteristics and Backwater Density

A very strong relationship was found between spring runoff flows and density of
NNC for the four year period, 1992 to 1995. The two highest runoff years (1993 and
1995) had the lowest NNC densities in habitats sampled in the following summer, fall and
spring (pre-runoff) collections (Table 7). Mean NNC density was three times higher in
summer and fall samples in the two low runoff years (1992 and 1994) than the two high
years (1993 and 1995) (Table 7). The mean NNC density for the two low runoff years was
six times greater in the (spring) pre-runoff samples than the high year average.

Density estimates for NNC also varied seasonally. Non-native-cyprinid (NNC)
densities peaked in the fall indicating recruitment of young fish during the summer period.
Densities were reduced in the spring indicating over-winter mortality (Table 7). In the