7835

• UCREFRP Catalog Number: 7835
• Author: Osmundson, D. B., et al.
• Title: Studies Of Colorado Squawfish In The Upper Colorado River, Final Reports.
• USFW Year: 1997.
• USFW - Doc Type: Recovery Implementation Program, Project No. 14,
• Copyright Material: NO

trammel nets were representative of the population, we assumed that they were because the
technique actively trapped all fish in confined areas, thereby greatly reducing or eliminating
the possibility for size selectivity, i.e., differential trap shyness, escapement ability, or
susceptibility to electric fields. Survival estimates were therefore calculated for fish z 550 mm
TL using only data from fish captured with trammel nets.
Estimates
For the combined years of 1991 through 1994, suitable survival rates ranged from 0.83 to
0.88 (P < 0.05). Only a relatively narrow range of estimates were not significantly different
from the measured distribution, even with P < 0.001 (Fig. 5). The best fit for the measured
distribution was for a survival rate of 0.86 (Fig. 6). Similar but broader ranges of survival
were estimated for individual years; these broader ranges and resulting variation among years
resulted from smaller sample sizes. When data from all years were combined, a range of
suitable survival rates narrowed to 0.84-0.86 (Table 3). For a theoretical population without
a stable age distribution, the effect on survival rate would be a change of approximately 1 %
for each percent of population increase or decrease (Table 4). Estimated survival rates were
the same when growth rates for fish _z 550 mm TL used in the calculations of the stable length
distributions varied by fish size (as shown in Table 2) or when they were assumed constant (as
in Fig. 3c). The 20 simulations of stable-age distributions conducted using different random
number sequences produced identical suitable survival rates, and nearly identical K-S d-value
test statistics.
0.6
0.5
a) 0.4
0.3
0.2
0.1
0
P = 0.001
-------------------- ------------ ---------
P = 0.05
0.6 0.7 0.8 0.9
Survival rate (fraction)
Figure 5. Kolmogorov-Smirnov d-statistic for test between stable size distributions and
measured distribution for Colorado squawfish Z 550 mm TL captured between 1991 and
1994. Dotted lines represent the d-value for P = 0.001 and P = 0.05. Lesser d-values have
lower significance levels. Examples of observed and theoretical length distributions of three
survival rates and associated statistics are shown in Fig. 6.
A-13