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968 PETERSEN AND PAUKERT TABLE 5.-Final parameter values used in the bioenergetics model of juvenile and subadult humpback chub. Except for SDA, the consumption and respiration parameters, were based on Monte Carlo filtering of humpback chub growth at 24°C. The parameters for SDA, FA, and UA are from other species, so no variance was associated with these values. Parameter abbreviation Description Mean (SD) Coefficient of variation (%) Consumption CA Intercept 0.154 (0.027) 17 CB Slope -0.251 (0.028) 11 CQ Consumption Q10 2.39 (0.19) 8 CTO Optimum temperature 28.1 (2.3) 8 CTM Maximum temperature 31.5 (2.5) 8 Respiration RA Intercept 0.0049 (0.0026) 53 RB Slope -0.084 (0.039) 47 RQ Respiration Q10 2.42 (0.17) 7 RTO Optimum temperature 28.2 (2.3) 8 RTM Maximum temperature 31.6 (2.4) 8 ACT Activity 1.16 (0.41) 36 SDA Specific dynamic action 0.15 Excretion and egestion UA Proportion of excretion 0.1 FA Proportion of egestion 0.1 (Figure 3). Regardless of food availability, pre- dicted growth rates for juvenile and subadult humpback chub were zero or negative at temper- atures above approximately 31°C. For juvenile humpback chub, the predicted growth rate was fairly constant across a broad range of temperatures (-5-25°C) when food avail- ability was in the range of 0.4-0.6 (Figure 3A). For example, with a food availability of 0.5, growth rate varied little from 5 to 27°C. When food availability was relatively low (p < 0.3) growth rate was negative for all temperatures. For subadult humpback chub, growth rates were negative or zero when food availability was low (p < 0.5) for all temperatures examined (Figure 3B). The spe- cific growth rates predicted across a fairly broad range of food availability and temperature is con- sistent with observed growth rates from laboratory and field studies (compare Figure 3 and Table 3), suggesting the model is operating within the ex- pected range. Bioenergetic Simulations of a Potential Temperature Control Device Scenario Before the completion of Glen Canyon Dam in 1963, average monthly water temperature through the Grand Canyon ranged from about 5°C to 27°C (Figure 2). Since the dam was constructed, water temperature has varied across a narrow range (9- 12°C; Figure 2). Bioenergetic model simulations suggest that before the dam was built, juvenile humpback chub may have grown from 4 to 22 g during 1 year; since the dam, 4-g juveniles grow to only 12 g (Table 6). Over twice as much food was required to achieve the high rate of growth under high temperatures prior to dam construction (Table 6). When we assumed an increased summer- fall temperature from a TCD and average (p = 0.65) food availability, juvenile size at the end of 1 year increased 33% compared with the size pre- dicted with post-dam temperatures (12 g versus 16 g; Table 6). Juvenile humpback chub would have to eat about 76 g of food (+58% relative to post- dam average conditions) to achieve this increase in size. With a slight increase in prey availability (p = 0.75), juvenile humpback chub grew to 24 g (+100%), requiring 106 g of prey (+121%; Table 6). Predicted growth of subadult humpback chub differed little between pre-dam, post-dam, and in- creased temperature scenarios. The food required to maintain this constant size varied from 378 g for post-dam conditions to 516 g (+37%) and 709 g (+88%) in the increased temperature and pre- dam conditions, respectively, due to the higher temperatures in these simulations. If prey avail- ability increased (p = 0.75) during a TCD appli- cation, subadult humpback chub grew to 158 g (+28% relative to post-dam average conditions), requiring 657 g of prey (+74%; Table 6). Discussion Bioenergetics Model Development Estimating bioenergetic parameters using the Monte Carlo sampling procedure was relatively A 4 g start 15 B 119 g -tart 0.4 0.2 P? "I 15 FIGURE 3.-El range, 0.1-1.0) a growth of a (A) subadult (starting a bioenergetics over 365 d. Grov simple, and thi tions for other periled species, ing collecting p ple size becaus. individuals that appropriate size tions. Laborato may also be su types of experin tality rate for e gered, or imper great concern 1