Edwards Associated tunas and dolphins in eastern tropical Pacific 



681 



40 50 60 70 80 90 100 110 120 130 140 150 160 

 FORK LENGTH (cm) 



Figure 3 



Sizes and ages of yellowfin tuna Thunnus albacares caught 

 with and without dolphins in the eastern tropical Pacific 

 Ocean, and length-interval during the first year of life by 

 spotted dolphins Sterwlla attenuata. Data include all years 

 1975-84, all areas fished, all fleets (U.S. plus non-U. S.). (Un- 

 publ. data from Ashley Mullin, lATTC, La Jolla). 



meters, based on weight-length measurements from a 

 sample of 50 spotted dolphins ranging in size from 82 

 to 210cm TL. 



Equations Each model included equations for specific 

 rates of consumption (Cgp), respiration (Rgp; including 

 both swimming activity ACT^p , and standard metab- 

 olism STDsp), heat of digestion (specific dynamic ac- 

 tion, SDAgp), and waste losses (excretion plus eges- 

 tion; WLgp). Specific rate of growth is estimated sim- 

 ply as the difference between consumption and the sum 

 of energy expenditures. 



The form of the equation for each specific rate was 

 the same for both models, with the exception of Rgp , 

 which was estimated for yellowfin using Boggs' (1984) 

 experimental results. Rgp was estimated for dolphins 

 following Magnuson's (1978) procedure for estimating 

 cost of swimming by carangiforms. 



No effect of water temperature on consumption or 

 respiration rates appears in either model. Ambient 

 water temperature was assumed to be constant at 

 27°C, as most of the tuna-dolphin habitat occurs in 

 waters of this temperature. 



Fish. Sci. Cent., La Jolla, unpubl. data). Proportions 

 of nursing calves (ages 0-2 yr), adolescents (ages 3-14 

 yr), sexually adult males (ages 15 and up), and sexual- 

 ly adult females (ages 1 1 and up) in an average school 

 were 0.05, 0.40, 0.25, and 0.30, respectively. Propor- 

 tions of adult females not pregnant or lactating, lac- 

 tating, pregnant, and pregnant and lactating animals 

 were 0.05, 0.15, 0.08, and 0.02, respectively. 



Weight-length conversions The tuna model used, 

 as the calibration growth curve, the Gompertz fit de- 

 rived by Wild (1986) for yellowfin tuna from the ETP. 

 When necessary, body fork lengths in centimeters 

 (cmFL) were converted to wet weights in grams 

 (WWg) using the length-weight relationship (Alex 

 Wild, lATTC, La Jolla, unpubl. data for yellowfin tuna 

 from the ETP) 



The calibration growth curve for expected size-at-age 

 in spotted dolphins was derived from equations and 

 figures in Hohn and Hammond (1985) and unpublished 

 data (A. Hohn, Southwest Fish. Sci. Cent., La Jolla). 

 Weight-length conversions assumed the relationship 



WWkg = 1.4* 10-5 *TL2-95, 



where WW^g is wet weight in kilograms, and TL is 

 total length (tip of rostrum to fluke notch) in centi- 



Consumption Specific rate of consumption (Cgp; 

 calories food consumed • calories of animal "^ • day-^) 

 was estimated as 



C,. = CONS,,,/CAL.. 



-■sp 



CALan is total caloric content of an individual 

 yellowfin or spotted dolphin, estimated as a function 

 of wet weight in grams. 



CAL, 



CD* WW, 



g' 



where CD is caloric density (cal/g wet wt) of yellow- 

 fin tuna^ or spotted dolphins^. 



CONSea] is total calories consumed per individual 

 per day, estimated as 



CONSeal = CONSind*CDf, 



where CDf is caloric density of food (cal/g wet wt) for 



' 1440 cal/g wet wt (Boggs 1984). 



-CDj = 1860 cal/g wet wt; average caloric density of four dolphins 

 measuring 81-189cmTL. Caloric density of each animal was deter- 

 mined as the sum of calories contained in blubbler, muscle, viscera, 

 and bone divided by total animal wet weight in grams. Average 

 caloric density of individual dolphins ranged from 1985 cal/g wet 

 wt in the 81 cm animal, to 1760 cal/g wet wt in the large adult female 

 (189cmTL). Assuming constant energy density for spotted dolphins 

 is acceptable, as spotted dolphins do not appear to exhibit any signifi- 

 cant seasonal, and little age-related, changes in thickness of their 

 blubber layer. 



