FISHERY BULLETIN: VOL. 74, NO. 1 



of the total drag on the test animals was derived 

 relative to his graphed observations as a function 

 of Re. From Re, one can determine the approxi- 

 mate coefficient of total drag (C^) from the 

 relation: 



Cd= 0.262 e -4-805 X 10- i?. 



(4) 



Gooding also reported respiration data for 

 skipjack, ranging from 45 to 53 cm, swimming at 

 or near Vioo where S^otai = 1.403 mg Oa/h. These 

 test animals had also been deprived of food for 

 24 h. Assuming / = 50 cm: 



Wmet= 523.5 g; Vioo = 70.5 cm/s; 

 Re = 3.525 x 10^ 

 S„ = 156 mg Oa/h; 



Cd = 0.262 e-^-^^^ " "^'^ '^-^^^ ^ '°' = 0.048. 

 /.S, = 2.59 X 10-5 (50)2(70.5)3(0.048) 

 = 1,233 mg Oa/h. 

 Ss+Sn, -S,,,,i = {1,233 + 156} mg O2 



= 1,389 mg Oa/h, (expected) 

 where S total = 1,403 mg 02/h, (observed) 

 leaving 14 mg 02/h, (difference). 



The Relation (4) we have used for Q as a function 

 of Re appears to be adequate for our purposes. 



Within the factors M^ and C^ there are an in- 

 separable pair of modifying effects which must 

 be accounted for, but which are essentially in- 

 determinate at the present state of the art. One 

 is the mechanical propulsion efficiency, and the 

 other is the effect of the short-term flux of the 

 rates of acceleration due to caudal fin position 

 and velocity wdthin a single tail beat cycle on 

 the "average" calculations of M^ and C^. The Me 

 and Q values are continuous variables within 

 the tail beat cycle and are inextricably bound 

 together. Where in the integration and estima- 

 tion of these two values the trade off is made is 

 inconsequential due to the equal and direct 

 effect of the estimate of one on the other value. 

 Until either value is measured and fixed, the 

 other coefficient is relative and therefore not 

 necessarily realistic. 



The effect of velocity on propulsion efficiency 

 is probably great in tunas (and other large 

 organisms) due to several processes, including 

 local heating phenomena and subsequent con- 

 traction rate increases of the muscle fibers 



(Walters 1962; Sharp and Vlymen^). The graded 

 increase in utilization of white muscle fibers as 

 velocity is increased should result in generalized 

 heating and increased overall efficiency of the 

 energy conversion processes in the muscles. This 

 and other effects may indeed account for the con- 

 siderable efficiency changes in work done as com- 

 pared to respiration rate when extended periods of 

 white muscle utilization are monitored (Kutty 

 1968). 



The higher scombrids {Auxis, Euthynnus, 

 Katsuwonus, and Thunnus) have incorporated, 

 in various designs, a subcutaneous vascular 

 system which is the distribution mechanism for 

 transport of arterial and venous blood to and 

 from the warm swimming musculature (Kishi- 

 nouye 1923). The direct transport of "warm" 

 venous blood to the fish's surface probably 

 affects the hydrodynamics of the fish and con- 

 tributes to the dynamic flux of the Cd value. Since 

 no data are available for these phenomena, they 

 have to be ignored in this treatment of the swim- 

 ming energetics, but future laboratory studies 

 should not ignore or delete these potential 

 effectors. 



Considering the range of possible error in 

 estimating both muscle efficiency and/or the co- 

 efficient of total drag, the close agreement be- 

 tween observed and expected respiration rates 

 indicates that we have useful estimates of energy 

 requirements. 



The only available respiration-activity data 

 from tunas is for K. pelamis. Assuming that 

 Magnuson's (1973) empirical relations and 

 density multipliers are representative of the 

 relative hydrodynamic status of the several 

 species, these relations should give a similarly 

 good approximation of energy consuming proc- 

 esses in T. albacares as they appear to give for 

 K. pelamis. 



The three continuous energy consuming pro- 

 cesses are, therefore, roughly accountable using 

 the previously described relations. The conver- 

 sion of oxygen consumption to caloric utiliza- 

 tion is made on the basis that 3.359 cal are avail- 

 able from 1 mg O2. Apparently the major energy 

 consumption process is swimming, including 

 feeding and flight behavior. The_energy ex- 

 pended is a function of the velocity Vjyp which is 



^Sharp, G. D., and W. J. Vlymen III. The relation between 

 heat generation, conservation and the swimming energetics 

 of tunas. Manuscr. 



42 



