8177

• UCREFRP Catalog Number: 8177
• Author: Valdez, R. A., B. R. Cowdell and L. Lentsch.
• Title: Overwinter Survival of Age-0 Colorado Pikeminnow in the Green River, Utah, 1987-1995\
• USFW Year: 1999.
• Copyright Material: NO

(Table 2). Mean total lengths of the 1994 cohort for fall (43 mm) and spring (63 mm) were greater
than for all other cohorts, while mean total lengths of the 1995 cohort for fall (26 mm) and spring
(31 mm) were smaller. Increases in mean total length (Le., average overwinter growth) from fall to
spring for the 1987-95 cohorts, with exception of the 1995 cohort, ranged from 4 mm to 10 mm.
Increase in mean total length for the 1994 cohorts was 20 mm.

Overwinter survival index of age-O Colorado pikeininnow in Reach 3 was evaluated for
length of fish in fall; flow variability, expressed as cumulative flow slope; water temperature,
e:\pressed as cumulative temperature slope; average backwater depth; and fall density of non-native
fishes (Table 3, Figure 4), in order to test the four principal hypotheses presented earlier in this
paper. There was no apparent relationship between survival index and total length of age-O fish in
t'all (P=0.705), with a poor fit of the data to a linear model (i=0.024). Flow slope showed a negative
relationship to survival index (P=0.285), with a poor fit of the data to a linear model (i=0.146).
\Vater temperature slope showed a weak positive relationship to survival index (P=0.344) with poor
fit of the data to a linear model (r=0.007), and fall densities of non-native fishes showed a negative
relationship to survival index (P=0.350), with a poor fit of the data to a linear model (i=0.118).
However, there was a significant relationship (r=0.744, P=0.0417) between greater average
backwater depth and higher survival index. Backwaters deeper than 120 cm mean depth had
significantly higher survival of age-O Colorado pikeminnow than shallower backwaters. There was
a strong relationship (r=0.950, P=<O.OOI) between fall and spring CPUEs (Figure 5).

Table 3. Variables tested to evaluate overwinter survival ofage:-O_Colorado pikeminnow.
Year Class Survival Fall TL. Cummulative Cummulative Cummulative Non-Native
(Percent) (mm) Flow SlopeI Flow Variance I Temperature I Fish Density
(CPUE)
1987 23 34 0.359 1.239 0.356 10.5
1988 38 38 0.197 1.193 0.354 43.4
1989 45 36 0.191 0.285 0.471 31.2
1990 93 40 0.199 0.245 0.396 23.1
1991 38 37 0.281 0.314 0.498 31.8
1992 100 37 0.204 2.106 0.461 13.6
1993 61 37 0.343 0.614 0.386 11.4 .
1994 37 43 0.228 0.262 0.461 70.9
1995 49 26 0.201 0.221 0.486 14.3
I coefficient of variation

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