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Fishery Bulletin 90(4|. 1992 



yellowfin tuna^ or spotted dolphins^, and CONSjnd is 

 wet weight in grams of food consumed, estimated as 



CONSind = C™ax*Pval*WWg, 



where C^ax is maximum possible consumption (ex- 

 pressed as a fraction of wet weight) for the largest 

 yellowfin or dolphin, estimated as 



r ^ r *WW cti 



where ^Ca = 1.2 and ^Cb = -0.22 for yellowfin, or ^Ca 

 = 3.98 and 8Cb = -0.29 for spotted dolphins. 



Pvai is an iteratively fitted unitless value in the 

 range 0-1 that, when "correct," results in the simu- 

 lated growth curve matching the observed growth 

 curve (University of Wisconsin Sea Grant 1989), and 

 WWg is body wet weight in grams. 



Respiration (yellowfin tuna) Specific rate of respir- 

 ation (Rspi calories respired • calories of animal "^ • 

 day~^) for yellowfin tuna was estimated as 



Rsp = (STD„-(-ACT„)*(20650/CD), 



with energy costs of standard (STD^^.) and active 

 (ACTw) metabolism expressed in watts. The factor 



^Energy density of yellowfin food was based on an assumed diet of 

 70% fish, 20% squid, and 10% inverteljrates (Olson and Boggs 1986). 

 with undigestible fractions of 0.124, 0.066, and 0.025, and caloric 

 densities of 1440, 1260, and 1000 cal/g wet wt, respectively. Average 

 ingested energy density (including the undigestible fraction) is 1380 

 cal/g wet wt. 



'Energy density of spotted dolphin food changes with age (size). 

 Spotted dolphins nurse throughout their first year (Perrin et al. 

 1976). They do not begin to ingest solid food until their second year, 

 and they do not stop nursing entirely until their third year when 

 they are ~145cm in length. In this simulation, dolphins up to 1 yr 

 of age were assumed to consume only milk (2855 cal/g wet wt) 

 (Pilson and Walker 1970). Diet during the second year was assumed 

 to be the same as that for yellowfin tunas, with an ingested energy 

 density (CD,) of 1380 cal/g wet wt. 



''Based on the assumption that maximum specific feeding rate for 

 very large yellowfin tunas (95000 g wet wt) would not exceed 10%/ 

 day, then solving for the intercept C^ (i.e., C,, = 0.10/(95000-"") 

 yields 0^= 1.2. In practice, the exact value chosen for C„,„ is flex- 

 ible, as higher values simply reduce the fitted value of P^j, , and 

 vice versa. 



''By analogy to walleye Stizosledion vitreum (Kitchell et al. 1977). 



'Assuming maximum possible ration for adult spotted dolphins 

 (~75kg) would not exceed 15% of body weight/day (Sergeant 1969), 

 and with C„„ = 0.15, WW =85000g, and C„= -0.29, then C,,= 

 3.98. 



"As a compromise between the unresolved arguments of Kleiber 

 (1961; Cb= -0.25) and Heusner (1982; 0^= -0.33) for scaling of 

 metabolic rate with size in mammals. This compromise was chosen 

 because consumption is not strictly a metabolic rate. While 

 Huesner's argument for metabolic rate is supported by data for 

 metabolic rate changes with size (see formulation for dolphin respira- 

 tion), no such data exist for consumption rates. 



20650 converts watts to cal/day. Dividing by caloric 

 density of the animal (CD) produces the specific rate. 

 Weight-specific energy cost of standard metabolism 

 for yellowfin was assumed constant for all sizes of 

 yellowfin (Boggs 1984) as 



STDw = 0.464 watts/g wet weight. 



Energy cost of active metabolism (watts/g wet wt) 

 was estimated using Boggs' (1984) equations and data 

 for energy costs of activity in yellowfin, 



ACT^. = F*VLG*FLH, 



where VL is velocity in cm/sec and F( = 1.59 £"■*), 

 G( = 1.64), and H(= -1.28) are fitted parameters de- 

 rived from Boggs' (1984) laboratory studies on 

 yellowfin energetics. 



Yellowfin were assumed to swim at length-specific 

 optimum-sustained cruising speeds, with velocity scal- 

 ing to fish length as 



VL = VLa*FLVLb, 



where 9VLa = 20.6, and i"VLh = 0.4. 



Respiration (spotted dolphins) Specific rate of re- 

 spiration (Rsp; calories respired ■ calories of animal "^ 

 ■ day"^) for spotted dolphins was estimated as 



R. 



sp 



(ACT,p + STDsp + HL,3p), 



where ACTgp is specific rate of swimming activity, 

 STDgp is specific rate of standard (basal) metabolism, 

 and HLrsp is specific rate of residual heat loss. 



Specific rates of swimming activity and standard 

 metabolism are estimated as 



and 



ACT.p = ACT,ai/CAL 



STDsp = STDeai/CAL 



Caloric cost of standard metabolism was estimated 



as 



STDeal = Sa*WW Sb, 



"Intercept estimate based on lOOcniFL yellowfin swimming on 

 average 130cm/sec in situ (Holland et al. 1990). 



'"Slope estimate based on theoretical and empirical studies by Weihs 

 (1973, 1981). 



