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spontaneous rates. Beyers and Plampin (Report C) measured metabolic rates of Colorado pikeminnow in <br />a swimming respirometer and reported that at 1.5°C, 42- to 46-mm TL fish could swim continuously for a <br />minimum of 6 h at a velocity of 1 bl/s, but not at 2 bl/s. <br />Bioenergetics Model Component <br />Bioenergetics modeling predictions suggest that overwinter survival of age-0 Colorado <br />pikeminnow may be negatively affected if fish activity increases in response to human-induced changes <br />in the environment. Simulations showed that fish mass and condition consistently decline when water <br />temperatures are below 5°C. Mass and condition of fish decline faster when activity is increased because <br />energetic reserves must be used to offset the cost of higher metabolic rate. <br />Activity rates of age-0 Colorado pikeminnow in the Green River during winter are unknown <br />because direct observations of fish are difficult to obtain. Consequently, the approach used in this <br />investigation was to evaluate outcomes of realistic ranges of potential conditions including water <br />temperature regimes, activity rates, and food consumption rates. Of the factors investigated, fish activity <br />rates had the greatest influence on overwinter survival of age-0 Colorado pikeminnow. When activity <br />rates were at a relatively low spontaneous level, or at a moderate level of 0.5 bl/s, fish survived to the end <br />of the 118 d winter period. When activity was a relatively high level of 1 bl/s, age-0 fish did not survive <br />to the end of the winter period regardless of their size. <br />xv