Edwards: Allometry of energetics parameters in Stenella attenuate 



437 



WET WEIGHT (kg) 



Figure 9 



Relationship between energy density (per gram dry weight) of 

 blubber (11 specimens), muscle (9 specimens) and bone (5 speci- 

 mens), and total wet weight of body in kilograms for spotted dol- 

 phins {Stenella attenuata) from the eastern tropical Pacific Ocean, 

 both sexes and all ages (sizes) represented. Lines through points are 

 fitted regressions. 



cetacean population preying on a fisheries re- 

 source (e.g., Overholz et al., 1991). 



The practical significance of these results for a 

 given population's estimates will depend on 

 values chosen for a number of parameters in 

 addition to those presented here (e.g., ambient 

 temperature, average swimming speed, size 

 composition of the population). Such calculations 

 are beyond the scope of the present study, but 

 these results for spotted dolphins from the ETP 

 show that allometric trends should be considered 

 in such calculations. Similar effects probably oc- 

 cur in other cetacean populations and should be 

 investigated. 



Caveats 



The regressions presented here include data from 

 a number of "neonate" dolphins which were actu- 

 ally late-term fetuses rather than true neonates. 

 Specimens of true neonates are rare. But the rela- 

 tively smooth fit through data collected from near- 

 term fetuses and first to third-year juveniles im- 

 ply that the physical characteristics predicted for 

 the under-sampled size ranges from 5-30 kg wet 

 weight, if one uses the regressions presented here, 

 are likely to be accurate. 



The large water content of bone and blubber 

 in fetal specimens probably reflects conditions 

 that change rapidly after birth, when fetal nu- 

 trition changes from placental to milk-derived. 

 It is not possible with the present data set to 

 identify exactly how quickly water content de- 

 creases. However, errors in energetics estimates 

 resulting from inaccurate estimates of bone wa- 

 ter content will be negligible owing to the rela- 

 tively small contribution made to energy flux by 

 skeletal materials. Errors in estimates of water 

 content of blubber for spotted dolphins in the 

 weight range 5-30 kg wet weight could be more 

 serious. Although the true extent of the problem 

 cannot be determined from this data set, pos- 

 sible values for this size range vary from about 

 15% to 30% (Fig. 10). 



Changes in maternal body composition (and 

 thus energetics estimates) during pregnancy and 

 lactation may occur in spotted dolphins as they 

 do in large whales (Lockyer 1981, a and b) but 

 such changes, if they occur, are apparently much 

 more subtle in spotted dolphins from the ETP. No 

 dramatic differences in body fractions or energy 

 density of blubber or muscle were discernable in 

 the set of specimens analyzed during this study, 

 which were collected from a variety of times and 

 places. It is unlikely that major changes occur in 



