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tit June 1990 e Tyus and Nikirk-Abundance, growth, and diet of [ctalums punctatus 191 were> 500 mm TL, even though sampling with baits presumably selected for larger fish (Ran- dolph and Clemens, 1976). Although sample size of older fish was too small (one to seven fish) for a realistic approximation of incremental growth, average annual growth increments for the first 15 years ranged from 17.2 to 53 mm TL. Growth was greatest in the first year and declined subsequently. Fish attained av- erage lengths >400 mm at age 9 and average lengths > 599 mm by age 17. Mean back-calcu- lated lengths at each annulus indicated that growth in the Green River system was much less than that of channel catfish in the midwestern and southwestern United States (reviewed by Car- lander, 1969, and Allen and Roden, 1978). How- ever, the length-weight relationship we obtained in the Green River basin (log WT = 3.12 log TL - 5.41) was similar to that reported for other locations (Carlander, 1969), suggesting the fish were healthy. The long life span (maximum 22 years) of our fish was remarkable. Even though ages of almost 40 years are reported (Moyle, 1976), a maximum of 6 to 10 years is usual (Davis, 1959; Moyle, 1976; Robison and Buchanan, 1988). Twenty- four percent of the fish we aged (n = 89) were judged older than 10 years. Slow growth of channel catfish in the Green and Yampa rivers may be due to limited re- sources, suboptimal temperature regimen, short growing season, and other unfavorable riverine conditions. Channel catfish do not grow well at water temperatures below 21 to 220C (Canfield, 1947; McCammon and LaFaunce, 1961; An- drews and Stickney, 1972; Randolph and Cle- mens, 1976), and water temperature in the Green River exceeds 210C only from mid-July to early September (ReMilliard et al., 1988). We as- sumed that little or no growth would occur from October through May and that growth may be slight in years when average daily water tem- peratures do not reach 21 DC or do so for only a few days. In addition, because the fish may ac- tually experience weight loss below 150C (Hei- dinger, 1975), some weight loss could occur in catfish in the Green River basin. Sizes of age 0 channel catfish captured in Oc- tober in 1979 to 1985 (Fig. 2) were inversely related to the river discharge (r = -0.83; P = 0.02), and positively related with water temper- ature (r = 0.88; P = 0.01) during the preceding July to September period (Fig. 3). The small size and low numbers of young channel catfish col- lected in October seine samples in 1982 to 1984 (average TL = 33 mm, n = 144; Fig. 2) was presumably due to inundation of shallow shore- line nursery habitats by unusually high summer flows (range of 108 to 253.6 m3/s), rather than a direct response to increased water velocity. These shoreline embayments were about 1.5 times more numerous during years of low-to-average dis- charge (years = 1979 to 1981 and 1985; discharge = 62.4 to 80.2 m3/s) and the young fish were larger and more abundant during these years (av- erage TL = 47.3 mm, n = 460; Fig. 2). Aerial photographic mapping by the Bureau of Recla- mation in 1986 to 1988 also revealed that em- bayments were reduced in area when flows in the Green River increased above average summer flows (M. J. Pucherelli, pers. camm.). Growth response to Green River temperatures was sim- ilar to that reported by others, and average tem- peratures recorded during the summer growth period (18 to 220C, Fig. 3) did not approach the 30 to 35DC optimum reported by Layher and Maughan (1985). We detected no difference in growth (for ages 1,3,5,7, and 9; ANOYA; P= 0.48) or condition factor (ANOY A; P = 0.24) between low and high gradient river reaches that varied greatly in hab- itat conditions. This suggested either that channel --1 FIG. 2-Size of age-O channel catfish captured in the Green River in October, 1979 to 1985. Collections in low-to-average water years (upper) were made with July-September flows as follows; 1979 = 78.9 m3/s, 1980 = 67.1 m'ls, 1981 = 62.4 m'ls, 1985 = 80.2 m'/s. Collections in high flow years (lower) were made as follows: 1982 = 108 m'ls, 1983 = 253.6 m3/s, 1984 = 157.7 m'/s. Discharge data from U.S. Geological Survey gauging station, Jensen, Utah. FIG. 3-Mean length of age-O channel catfish captured in October, 1979 to 1985, relative to average of daily water temperatures (upper) and river discharge (lower) during the preceding July-September growth period for each respective year. Discharge and daily temperatures from U.S. Geological Survey gauging station, Jensen, Utah.