FISHERY BULLETIN: VOL. 79, NO. 1 



2 3 4 



SWIMMING SPEED ( lengths-sec"' ) 



FIGURE 9.— Relation of rate of oxygen uptake per unit distance (VQj) swam to 

 swimming speed for skipjack tuna of various lengths. The x's indicate characteristic 

 swimming speeds of fish in the present study. Sopt is the optimum speed for covering 

 distance in terms of minimum Vq^. The arrow at 1.43 lengths • sec ' is the optimum 

 speed predicted by Weihs' (1973b) model. 



characteristic of fish between 30 and 60 cm length 

 (Figure 10). 



In a subsequent paper, Weihs (1977) showed 

 that fishes' optimum swimming speeds on an 



absolute basis ought to be proportional to L"^^. 

 The characteristic speeds of our tuna, when com- 

 puted in centimeters per second and treated as a 

 power function of fish length, are proportional to 



100,000 



100 



;]-3800g 58 cm 

 ;]-2800g 54 cm 



;>l800g 48 cm 



i>-800g 38 cm 



3 4 5 6 7 



SWIMMING SPEED ( lengths- sec -' ) 



10 



Figure lO. — Comparison between the measured oxygen uptake relationship extrapolated between 

 and 8.5 lengths sec~* (broken lines) and the theoretically expected power consumption (solid 

 lines) for four skipjack tuna. Triangles (▲) are the theoretical power consumption based on a 

 detailed analysis of drag forces for a 40 cm, 1,003 g skipjack tuna (Magnuson 1978). Points (•) are 

 based upon a detailed analysis of thrust forces (Magnuson 1978). Length measures are fork length. 



44 



