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Last modified
7/14/2009 5:02:31 PM
Creation date
5/20/2009 10:22:15 AM
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UCREFRP
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
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study (Fig. 2). The stable age distribution for constant survival rate s was calculated using: <br />Ni = NFL*s*(1-9) <br />where Ni is the relative number of fish of age i and g is the annual growth rate of the <br />population. Simulations were conducted to select lengths for each age from the age-length <br />distribution. Lengths were randomly selected from these distributions for 10,000 fish of each <br />age, and the number of fish in 1-mm-TL increments was calculated by weighting the relative <br />number in each age class. Survival rates for which the measured distributions did not differ <br />significantly (P > 0.05) from the stable length distributions, using the Kolmogorov-Smirnov <br />(KS) one-sample test, were considered to be "suitable" estimates. <br />Tests of Assumptions <br />Statistical tests were conducted to assess whether the observed population structure was <br />consistent with the assumptions fisted above. Comparisons between length distributions of <br />fish captured in each year (1982, and 1991 through 1995) were made using the K-S two- <br />sample test to assess the constancy of the age structure between years. Stability in the age <br />structure would be consistent with relatively constant recruitment into the youngest age class, <br />and constant survival among years and over ages and lengths. We compared distributions of <br />fish captured with trammel nets with those captured with electrofishing (K-S two-sample test) <br />to determine whether all capture data could be used. Also, we used annual, trammel-net <br />catch rates of Colorado squawfish Z 550 mm TL as a measure to assess (ANOVA) whether <br />population abundance was relatively stable (i.e., g z 0) during 1991 through 1994. Though <br />effort among net sets was unequal, average effort of net sets was assumed equal among years. <br />RESULTS <br />Growth and Age <br />Growth of Colorado squawfish in the Colorado River is relatively rapid through about age 10 <br />(Tables 1 and 2). At this age, Colorado squawfish average approximately 550 mm TL. Our <br />estimates of mean lengths by age were similar to those reported by other researchers, but only <br />through about age 10 (Fig. 3a). Our estimate of mean age for fish 600 mm TL was 15 years; <br />for those 700 mm TL, 25 years; 800 mm TL, 32 years. Rate of growth slows after about age <br />10, although there may be a rate increase when fish are between 650 and 800 mm TL; beyond <br />800 mm TL, growth apparently slows again (Table 2). However, differences in mean annual <br />growth increments among all size classes > 550 mm were not statistically significant. Growth <br />rate differences among years (1991-1995) were not found for fish z 345 mm TL (ANCOVA, <br />df = 4, 71, F = 0.34, P = 0.85). Relationships between growth in one year and subsequent <br />years was not found for most individuals z 400 mm TL (df = 1, X2 = 0.024, P = 0.88). <br />A-8
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