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Fishery Bulletin 91(3). 1993 



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WET WEIGHT (kg) 



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WET WEIGHT (kg) 



Figure 8 



(A) Relationship between fractions of total body wet weight com- 

 prising muscle, blubber, and bone, and total wet weight of body 

 in kilograms for 24 specimens of spotted dolphin {Stenella 

 attenuata) from the eastern tropical Pacific Ocean, both sexes and 

 all ages (sizes) represented. Lines through points are fitted regres- 

 sions. (B) Relationship between fractions of total body wet weight 

 comprising viscera and fins, and total wet weight of body in 

 kilograms for spotted dolphins (Stenella attenuata) from the east- 

 ern tropical Pacific Ocean, both sexes and all ages (sizes) repre- 

 sented. Lines through points are fitted regressions. 



metric trends for estimates of population energy flux 

 are not necessarily straightforward. Dolphins less than 

 about 3 years old represent only about 10% of the 

 population in these relatively long-lived and slowly re- 

 producing mammals; dolphins age 3-12 compose 

 about 40% and sexually mature adults about 50% of 

 the population (Barlow and Hohn, 1984; Hohn and 

 Hammond, 1985). Because they are so few and be- 

 cause their biomass is so small, ignoring allometric 

 effects when estimating energy fluxes for the younger 

 animals, or ignoring the younger animals altogether, 



will have little direct effect on population energy 

 budgets. 



However, the indirect effects may be consider- 

 able. To the extent that activities of older animals 

 are constrained by energy-related characteristics 

 of young dolphins, indirect effects of size-related 

 differences in estimated energy fluxes may be more 

 important than the absolute fluxes themselves, 

 through regulating behavior or ecological relation- 

 ships. For example, muscle fraction of body mass 

 in neonate dolphins (5kg) is about 30% less than 

 the muscle fraction in adults (70 kg; Figure 8A, 

 Table 4). Thus the power available for swimming 

 (as a function of muscle mass) is 30%> less than 

 would be estimated based on measurements from 

 adult animals. The estimated speeds that small 

 dolphins, with their smaller muscle mass, can 

 maintain will be slower than speeds estimated by 

 simply applying to neonates parameter values de- 

 rived from adults. 



Differences in estimated swimming speed may 

 be important because dolphins are schooling 

 mammals with apparently strong social ties and 

 prolonged periods of parental care for nursing 

 offspring. In order to remain within the same 

 school, the average speed for all individuals will 

 be constrained to the slower speeds that can be 

 maintained by smaller dolphins. Estimates from 

 tagging studies of spotted dolphins in the ETP 

 indicate that in fact the average cruising speed 

 of dolphin schools is the optimum for neonates 

 rather than for adults, despite the fact that 

 adults represent the majority of individuals in 

 the schools (Edwards, 1992, and references 

 therein). Using parameters appropriate for adult 

 dolphins in estimates for the smaller animals 

 would produce unreasonably high estimates of 

 sustainable power output (and therefore food con- 

 sumption) by the smaller animals (Edwards, 

 1992). School speeds, and therefore energy re- 

 quirements to maintain these speeds, may thus 

 be constrained by energetics characteristics of 

 small animals that cannot be extrapolated sim- 

 ply from measurements on adults. As cost of 

 transport is a large fraction of the total energy re- 

 quirements of a swimming mammal (active metabo- 

 lism in swimming homeotherms [including dolphins, 

 sea otters, and penguins] is generally 2 to 3 times 

 that of resting metabolic rates [Hui, 1987]), main- 

 taining reduced speeds should reduce energy costs 

 and therefore forage requirements for the school mov- 

 ing as a unit. This is particularly significant because 

 forage requirements are the most commonly esti- 

 mated energy flux used to estimate the impact of a 



