>4 to 5 kg are extremely difficult to capture and 

 transport, it is unlikely that specimens larger 

 than this will be tested in the foreseeable future. 



Second, the SMR includes the energetic cost of 

 osmoregulation and cardiac work. The energy re- 

 quirement of both processes comprises a sig- 

 nificant fraction of the SMR (Heath 1964) and 

 more importantly, the energy demand of these 

 processes is dependent on swimming speed (Rao 

 1968; Farmer and Beamish 1969; Nordlie and 

 Leffler 1975). Therefore prediction of energy de- 

 mand as a function of swimming speed may not be 

 adequately determined by simple addition of the 

 SMR and the energj' cost of swimming based on a 

 theoretical estimate of hydrodynamic drag: an es- 

 timate of the increased internal work, due to activ- 

 ity, should also be included. 



Third, the scatter in the SMR's presented in 

 Figure 2 is due, in part, to the difficulty of working 

 with animals such as skipjack tuna, which are 

 both highly active and physiologically delicate. 

 There are, however, also at least two distinct sub- 

 populations of skipjack tuna that occur around the 

 Hawaiian Islands ( Sharp-' i. It is reasonable to sus- 

 pect the SMR of individuals from the various sub- 

 populations might be significantly different when 

 measured under identical conditions. Again, 

 reasonable caution in application of the data pre- 

 sented here is urged. 



■Acknow ledgments 



I thank the following people for helpful criti- 

 cisms of the manuscript and useful discussions: 

 Andrew Dizon, Gary Sharp, Don Stevens, Causey 

 Whittow, and Carol Hopper. Randolph Chang, 

 Douglas Davies, and Victor Honda provided tech- 

 nical assistance. 



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