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<br />211 The Southwestern Naturalist vol. 29. no. 1 <br />- <br />U 30 30 <br />0 26 26 <br />- <br />W 22 22 <br />a:: 18 18 <br />::> <br />~ 14 14 <br />a:: 10 10 <br />W <br />CL 6 6 <br />~ 2 2 <br />W <br />t- 350 A M J J A S 350 <br /> 300 300 <br />- <br />u 250 250 <br />Q) <br />~ <br />rt) <br />E 200 200 <br />- <br />W <br />~ 150 150 <br /><! <br />I <br />U <br />enlCO 100 <br />C) <br /> 50 50 <br /> <br /> <br /> <br />(!) <br />Z <br />Z <br />~ <br />a: <br />en <br /> <br />A M J J A S <br />1980 <br />(46) <br />- <br />6/16-8/2 <br /> <br />A M J J A S <br />1981 <br />(23) <br />-- <br />6/25-8/3 <br /> <br />FIG. 3.-Relationship of temperature (upper) and discharge (middle) to estimated spawning <br />periods of Colorado squawfish (lower). YampaRiver (April-Sept., 1980 and 1981). Refer to Fig. 2 <br />for explanation. <br /> <br />flow regime is an important limiting factor both for spawning and larval <br />survival. For example, peak flows in both the Colorado and Yampa rivers <br />in 1981 (Figs. 2 and 3) were approximately 310 and 160 m3/secs, respec- <br />tively, and were substantially less than those observed in 1980 (approxi- <br />mately 850 and 330 m3/sec). Similarly, only one larval squawfish was <br />collected in the Colorado in 1981 while 77 were collected in 1980. In the <br />Yampa, 23 were collected in 1981 while 46 were collected the previous years. <br />Importantly, sampling effort (i.e. number of samples) in 1981 was actually <br />greater than in 1980 (Table 1). <br />