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carp ~prinus car io, channel catfish Ictalurus punctatus, black bullhead <br />Ameiurus melas, smallmouth bass Microaterus dolomieu, green sunfish <br />Le orris cvanellus, bluegill L. macrochirus, mottled sculpin Cottus bairdi, <br />and mosquitofish Gambusia affinis. <br />Growth and survival.-Young Colorado squawfish averaged 40 mm TL in <br />October (range = 29.0-47.3 mm), and the average annual size was the same <br />in the upper and lower Green River (39.7 upper, range = 29 - 46.3 mm TL; <br />39.9 lower, range = 30 - 47.3 mm TL). However, mean TL was different <br />between the two areas for five of the nine years studied (t-tests, P < <br />0.01), and the fish were larger in TL in the upper area in four of five <br />years (Table 5). <br />The relative abundance (loge x fish/100 m2) of age-0 Colorado squawfish <br />captured in October was inversely correlated with late summer flows in the <br />upper (strata D, E, F) and the lower (strata A, B, C) Green River. (r = - <br />0.87, P < 0.01 for upper). r = - 0.84, P < 0.01 for lower). Fish TL was <br />also inversely correlated with late summer flows, particularly in the <br />lower Green River (r = -0.81, P <0.01 lower; r = -0.57, P = 0.11, upper). <br />We were unable to detect a pattern of overwinter mortality in age-0 <br />Colorado squawfish. Spring catches (range = 0 to 289 fish/1000m2) were <br />greater than catches the previous autumn in four out of eight cases, and <br />these ranged from 0.24-2.08 times higher in the lower and from 0.73-9.15 <br />times higher in the upper Green River. Young Colorado squawfish caught in <br />spring were larger (x_ = 45.2, N = 1,194) than those caught in autumn (x = <br />42.3, N = 1,243). When partitioned into upper and lower Green River, the <br />mean TL of fish in March and April {x = 46.9, N = 191 upper, _x = 44.7, N = <br />1,003 lower) were greater than fish sampled in the same areas the <br />11 <br />