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The high gradient reaches of strata C (6.8/100m2), D (4.9/100m2) and G <br />(0.5/100m2) had lower catches (Table 2). <br />Hatching of Colorado squawfish was associated with declining water <br />levels following peak spring runoff, and lasted about 2-6 weeks, depending <br />on water flow. Hatching occurred earlier in years of lower peak discharge <br />(e.g., 1981 and 1987), and later in years of higher peak discharge (e.g., <br />1983-1984, Table 1). Hatching dates of larval Colorado squawfish were <br />related to peak spring flows. Fish captured in the Yampa and upper Green <br />rivers hatched about 54.0 d (range = 20 to 74) after maximum flows (r = <br />0.092, P = 0.01) and larvae in the lower Green River hatched about 40.0 d <br />(range = 8 to 55) after maximum flows (r = 0.88, P = 0.11). In both <br />spawning areas, earlier peaks and larger flows tended to lengthen the <br />time before hatching, whereas later peaks and smaller flows tended to <br />shorten the hatching response time. <br />Habitat Use.-Catch of young Colorado squawfish in 1979-1981 was <br />greatest in backwaters (18.8/100m2), shorelines (1.6/100m2), side channels <br />(1.5/100m2), runs (0.3/100m2), and eddies (0.3/100m2, Table 3). In all <br />years combined (1979-1985, 1987 and 1988), the catch of age-0 Colorado <br />squawfish averaged 13.3/100m2, or about 6.7 fish/backwater (range = 0- <br />316). The fish was absent in 37% and 59% of backwaters in the lower <br />nursery area (strata A and B) and upper nursery area (strata E and F), <br />respectively. <br />In autumn, Colorado squawfish occupied backwaters that were warmer and <br />deeper (t-tests, P < 0.05), and more turbid (G-tests, P < 0.01, Table 4). <br />Backwaters in which Colorado squawfish were present averaged about 2° <br />warmer than those with the fish were absent, regardless of average <br />9 <br />