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....... GROWTH AND SURVIVAL OF COLORADO SQUAWFiSH 691 TABLE I.-Estimated mean total lengths (TL) and mean annual growth increments by age for age-0-7 Colorado squawfish in the Colorado River. Mean length at hatching is from Snyder (1981). Mean TL at age I is from measured fish assumed to be I year old that were seined near river kilometer 87 (measured from the mouth of the Green River) on 28 June 1989. Mean lengths of fish age 2-7 are from measurements of fish aged by scales. Insufficient captures of age-2 fish precluded estimates of increments for ages 1-2 and 2-3. Increments for fish age 7-8 were not calculated because presumptive age-8 fish were not reliably aged. Growth Annual growth Age Total length (mm) period increment (mm) (years) N Mean Range SD (age) Mean SD 0 8 7.7 7.0-8.5 0.5 0-1 63.5 13.6 I 73 71.2 50-103 13.6 1-2 2 I 181.0 2-3 3 3 232.7 190-259 37.3 3-4 82.0 56.0 4 6 314.7 267-374 41.8 4-5 61.5 53.4 5 19 376.2 326-453 33.3 5-6 47.9 45.3 6 10 424.1 375-472 30.6 6-7 32.2 36.6 7 7 456.3 430-479 20.0 ble age distribution for constant survival rate s was calculated as Ni = Ni-I'S.(l - g), where Ni is the relative number of fish of age i and g is the annual rate of population growth. Sim- ulations were conducted to select lengths for each age from age-length distributions. Lengths were randomly selected for 10,000 fish of each age, and the number of fish in I-mm increments calculated by weighting the relative number in each age-class. Survival rates for which measured distributions did not differ significantly (Kolmogorov-Smirnov TABLE 2.-Estimated annual growth increments for Col- orado squawfish 400 rom total length (TL) and longer in the Colorado River. Mean increments are from measured changes in length of recaptured fish. Length-class is of fish at first capture. Mean growth increments with a letter in common are not significantly different (ANOV A, F = 13.63; df = 7, 119; P < 0.00001; Fisher's least significant difference, P < 0.05). A combined average increment for fish 550-899 mm TL is also shown because mean incre- ments among these sizes were not statistically different. Length- Growth age i to class age i + I (rnm) at age i (mm) N Mean Range SD 400-449 6 42.7w 28-52 8.1 450-499 17 30.1 x 5-68 18.9 500-549 24 19.8 Y 4-54 13.7 550-599 32 9.5 z 0-31 8.2 600-649 21 8.7 z 0-24 7.5 650-699 10 12.5 zy 3-24 7.9 700-749 6 14.0 zy 7-22 5.6 750-799 3 10.4 z 5-15 4.9 800-849 3 2.7 z 0-5 2.5 850-899 5 5.1 z 2-8 2.4 550-899 80 9.5 0-31 7.5 [K-S] one-sample test, P > 0.05) from stable length distributions were considered "suitable" estimates. Tests of assumptions.-Statistical tests were conducted to assess whether observed population structure of fish 550 mm and longer was consistent with the assumptions listed above. Comparisons between TL distributions in each year (1982, and 1991-1995) were made with the K-S two-sample test to assess constancy of age structure between years (see Figure 2). Stability in age structure would be consistent with constant recruitment into the youngest age-class of fish 550 mm and longer and constant survival among years and over ages and lengths. We compared length distributions of fish captured with trammel nets with fish that were electrofished (K-S two-sample test) to determine if all data could be used. We also used annual trammel-net catch rates of Colorado squaw fish 550 mm and longer to assess (ANOV A) if abundance was relatively stable (i.e., g = 0) during 1991- 1994. Though effort among net sets was unequal, average effort was assumed equal among years. Results Growth and Age Growth of Colorado squaw fish in the Colorado River was relatively rapid through about age 10, when fish averaged approximately 550 mm TL (Tables 1, 2). Our estimates of mean lengths by age were similar to reports by others, but only through age 10 (Figure 3). Our estimate of mean age for fish 600 mm was 15 years; 700 mm, 25 years; 800 mm, 32 years. Rate of growth slowed ,ftenge 10, >!though.. inurea.ein mte may OW" ~ when fi.h = betweeo 650 ..d gOO mm; beyond j