mocline, where it is hypothesized that thermal 

 stratification, and associated water density micro- 

 structure may lead to an aggregation of some part 

 of the fishes' food supply in thin layers. 



Acknowledgments 



This work was supported, in part, by the Na- 

 tional Marine Fisheries Service, NOAA, under 

 Contract 03-7-208-35037. The authors would like 

 to acknowledge the technical contributions of 

 David Doan and David Horton in the construction 

 of the electronics and the conduct of the measure- 

 ments. The advice, encouragement, and support of 

 Paul Smith, NMFS, is gi-atefully acknowledged. 

 Our appreciation is also extended to the reviewers, 

 both formal and informal, and the editor. 



Literature Cited 



Feller, W. 



1966. An introduction to probability theory and its appli- 

 cations. Vol. 2. John Wiley & Sons, Inc., N.Y.. 626 p, 



Hewitt, R. p., p. E. Smith, and J. C. Brown. 



1976. Development and use of sonar mapping for pelagic 

 stock assessment in the California Current area. Fish. 

 Bull.. U.S. 74:281-300. 



HOLLIDAY, D. V. 



1977. The use of swimbladder resonance in the sizing of 

 schooled pelagic fish, Rapp. P.-V. Reun. Cons. Int. 

 Explor. Mer. 170:130-135. 



Love, r. h. 



1977. Target strength of an individual fish at any as- 

 pect. J. Acoust. Soc Am. 62:1397-1403. 



Papoulis, a. 



1965. Probability, random variables and stochastic 



processes. McGraw-Hill, N.Y.. 583 p. 

 Revelle, R., and F. p. SHEPARD. 



1939. Sediments off the California Coast In P. D. Trask 



(editor), Recent marine sediments, p. 245-282. Am. Assoc. 



Pet. Geol. Tulsa. 



Squire. J, L., Jr. 



1972. Apparent abundance of some pelagic marine fishes 

 off the southern and central California coast as surveyed 

 by an airborne monitoring program. Fish, Bull,. U.S. 

 70:1005-1019. 



D, V, HOLLIDAY 

 H. L. Larsen 



Tracor, Inc., San Diego Laboratory 

 3420 Kenyan Street 

 San Diego. C A 92110 



THE EFFECT OF BODY SIZE ON 



THE STANDARD METABOLIC RATE OF 



SKIPJACK TUNA, KATSUWONUS PELAMIS 



The standard metabolic rate (SMR) offish is the 

 energy requirement of a postabsorptive animal 

 completely at rest (Beamish and Mookherjii 1964; 

 Fry 1971; Brett 1972). It approximates the energy 

 demand of all metabolic processes except swim- 

 ming and digestion. The SMR (and its relation to 

 fish size) is an important input parameter for 

 energetics, growth, and population models ( Kitch- 

 ell et al. 1974; Kitchell et al. 1977). The SMR may 

 also be used to predict optimal fish cruising speed 

 (Weihs 1973, 1977). I undertook this study to pro- 

 vide SMR measurements for skipjack tuna, Ka- 

 tsuwonufi pelamis. These measurements may be 

 incorporated into models such as those described 

 in Sharp and Francis 1 1976). Kitchell et al. ( 1978), 

 and Sharp and Vlymen (1978). 



The SMR is generally determined by extrapola- 

 tion of a metabolic rate versus swimming activity 

 curve back to a zero activity level (Beamish 1964; 

 Brett 196.5; Muir et al. 1965). However, because it 

 is difficult simultaneously to measure metabolic 

 rate and activity level of large, highly active, 

 pelagic species such as skipjack tuna, SMR was 

 measured directly. 



Methods and Materials 



Skipjack tuna, purchased from local fishermen, 

 were maintained at the Kewalo Research Facility 

 of the National Marine Fisheries Service (de- 

 scribed in Nakamura 1972). Fish were kept in 

 outdoor tanks from 2 days to several weeks before 

 use. Food was presented to all fish daily; however, 

 a fish was not fed for at least 20 h prior to its use in 

 an experiment. This allowed sufficient time for an 

 animal to clear its stomach and intestine and for 

 its blood glucose level to return to prefeeding 

 levels (Magnuson 1969). 



To reduce struggling and minimize injury dur- 

 ing handling, each fish was injected with the 

 neuromuscular blocking agent gallamine 

 triethiodide (approximately 1 mg kg '). The ani- 

 mal was then placed in a Plexiglas' flow-through 

 box respirometer, similar to that described in Ste- 

 vens ( 1972). The spinal cord was cut immediately 

 behind the skull to stop all overt muscular activity 



'Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



494 



FISHERY BULLETIN, VOL, 77. NO. 2. 1979. 



