FISHERY BULLETIN: VOL. 80. NO. 4 



0-3 



0-4 



0-5 



06 



0-7 



\ [A k Carcharhinus 



>i <r\ i me f° no P ferus 



\ \ Blacktip shark 



\ \\ 0-22 m.s" 1 





0-6 



0-7 



0-8 



0* M £ 



Sphyrna 

 tiburo 



Bonnethead shark 

 0-57 m.s" 1 



Triakis 

 semifasciata 



Leopard shark 

 0-56 m.s 



Figure 2.— Tracings from videotapes 

 of three species of sharks swimming at 

 three different speeds to show typical 

 body movements. The times above 

 each tracing are in seconds. 



fin trailing edge amplitudes tend to be constant 

 at about 0.2 L (see Hunter and Zweifel 1971). 



In those cases where specific amplitudes and 

 tail-beat frequencies have been related, their 

 product (JA/L) is linearly related to speed. A 

 similar relationship was calculated for this prod- 

 uct using the relationships derived for Triakis 

 by Hunter and Zweifel (1971) and was similar, 

 but slightly curved for the blacktip shark (Fig. 

 3E). The product fA/L also increased with speed 

 for the other species (Fig. 3F). The free-swim- 

 ming sharks thus showed frequency and ampli- 

 tude modulation with speed. This contrasts with 



Triakis henlei in a water tunnel where only tail- 

 beat frequency was modulated, perhaps due to 

 the presence of walls in the water tunnel. The 

 modulation of both tail-beat frequency and 

 amplitude with swimming speed explains the 

 differences in the kinematics-swimming speed 

 relationships between teleosts and sharks. It ap- 

 pears that the shark propulsive system is more 

 plastic than that of bony fish. 



Because of the interrelationships between tail- 

 beat frequency, specific amplitude, and specific 

 swimming speed, stride length also varied in- 

 versely with swimming speed for the blacktip 



806 



