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13 <br />Thermal units were then integrated into the monthly lake cove <br />temperatures to determine the approximate spawning dates. Fertilization <br />and 0°C were used as thresholds of time and temperature. <br />3.7 Physical Hydrodynamics <br />The effects of water level fluctuations on egg survival were <br />estimated by examining the intensity of spawning effort at various <br />depths in spawning areas. Observations were made from a bluff <br />overlooking a 40 m section of shoreline in Yuma Cove. Additional data on <br />the depth distribution of redds were obtained from Mueller et al. <br />(1982). Percent mortality of the hatch was estimated for each day of the <br />spawning season from the maximum water level decrease occurring during <br />the period required for hatching at respective monthly lake <br />temperatures. These water level decreases were then plotted against <br />depth distributions of redds to estimate the extent of dessication. <br />Hatching times were derived from laboratory studies, and water level <br />fluctuation data were provided by the U.S. Bureau of Reclamation. <br />Reservoir temperatures were again converted to thermal units (Heming et <br />al. 1982) for comparison with developmental thermal units calculated <br />from experimental hatching data. This aided in an assessment of the <br />interaction of development rates, temperature, and water level <br />fluctuations throughout the season. <br />3.8 Statistical Analyses. <br />Statistical analyses were performed with the SPSS (Nie et al. 1975) <br />statistical programs. Non-parametric statistics were used in length and <br />weight analyses. Kruskal-Wallis analysis of variance, Mann-Whitney <br />U-tests and Chi-square analyses were used where appropriate.