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 5. Correlations between peak flow, runoff season and drift season flow and
abundance of native, nonnative and Colorado pikeminnow larvae
estimated in the drift for the five study years.

Fish category Peak flow Runoff Season Drift Season
(mean of 31 (mean flow
highest flows) July 1 to Aug 15)
~ value
Native species 0.631 0.588 0.768
Nonnative species 0.313 0.347 0.160
Pikeminnow 0.394 0.383 0.838
r value
Native species 0.794 0.767 0.876
Nonnative species 0.560 0.589 0.400
Pikeminnow 0.628 0.619 0.915
Significance level (3df) at 0.05=0.878
Native species Rejected rejected Rejected
Nonnative species Rejected rejected Rejected
Pikeminnow Rejected rejected Not rejected
Probability for alpha
Native species 0.108 0.130 0.051 .
Nonnative species 0.327 0.296 0.504
Pikeminnow 0.257 0.266 0.029

UTAH COLLECTIONS (Trammel and Chart, 1999a and 1999b)

Colorado Pikeminnow - Catch Characteristics and Drift Estimates

The onset of spawning occurred earlier at Westwater than at Loma in 4 out of 5
years, probably a result of earlier warming, and indicates spawning is occurring between
Lorna and Westwater. However catch rates (fish/1000rn3), and estimates for total
transport abundance were lower at Westwater than at Loma in all five years (Table 6).

Seasonal drift densities for Colorado pikeminnow larvae at Loma were not
correlated with Westwater drift densities either in catch per 1000m3 (r2 = 0.002; Table 6),
or in total transport abundance (r2 =;; -0.43). The lack of strong correlations indicated
trends in abundance differed at these two sites. At Westwater the higher flow years had
higher Colorado pikeminnow densities with the highest in 1993, and the third highest in
1995, while in Loma this was reversed with the highest in 1995 and the third highest in
1993. The low flow years (1992 and 1994) ranked fourth and fifth, respectively in
Westwater but the ranking was second and fourth respectively at Loma. The largest
discrepancy in ranking was in the intermediate flow year (1996) which ranked second at
Westwater but was fifth at Lorna (Table 6).

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