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Field Data Inputs to the Model <br />Temperature regimes and energy expenditure associated with movement of individual fish were <br />obtained by radio-telemetry. Two sub-populations of pike were implanted with radio tags. Pike <br />from the Yampa River and the Ouray section of the Green River were implanted and monitored <br />for position and daily movement at least monthly. During May and June, pike greater than 350 <br />mm were captured, anesthesized with MS-222 and surgically implanted with internal radio <br />transmitters (30-40 MHz). Transmitters were placed in the body cavity through 30-35 mm <br />incisions that were sutured shut with catgut. Pike were released within one hour of implantation. <br />Movements were recorded at least monthly for all months except January 1994. Pike were <br />located by triangulation and positions were recorded by river mile. At least five pike were <br />followed continuously over a 24-h period on four separate occasions to determine diel movement <br />patterns. <br />Water temperatures were recorded whenever radio-tagged pike were located. Temperatures were <br />occasionally recorded over a diel sequence, and at least one temperature was recorded at one fish <br />position per month during May-November 1993. These temperatures compared favorably to <br />daily main channel temperatures measured at the Ouray National Refuge (US Fish and Wildlife <br />Service, unpublished data). Temperature records were entered into the model, and missing daily <br />values were interpolated by the model using a sine function. <br />Growth of northern pike was estimated by aging, measuring (total and fork lengths, mm), and <br />weighing (g) specimens collected during October 1993 and May-June 1994. Fish were captured <br />with electroshockers and trammel nets. Ages were interpreted by counting annuli on magnified <br />