WEBB and KEYES: SWIMMING KINEMATICS OF SHARKS 



lined caudal peduncle. Carcharhinus leucas, C. 

 melanopterus, and S. tiburo represent group 2. 

 Group 3 includes sharks with a low aspect ratio 

 tail, making a small angle to the horizontal, and a 

 less fusiform body, represented by G. cirratum, 

 T. semifasciata, and N. brevirostris. Group 4 in- 

 corporates the squaloid sharks, e.g., Centrolepis, 

 which were not available. 



Swimming movements were recorded on video 

 tape. Recordings were made above the free sur- 

 face of the public display facilities. Surface rip- 

 ples were small compared with the images of the 

 sharks and were therefore ignored. To avoid sur- 

 face problems, observations in the rectangular 

 tank were made from below through the trans- 

 parent bottom. Surface ripples did not deleter- 

 iously affect measurement accuracy because no 

 differences in data from the public facilities and 

 the rectangular tank could be found. 



Swimming records were obtained for as wide a 

 range of speeds as possible. In most cases, normal 

 variation in motor behavior due to the operation 

 of the park was exploited. For the large sharks, 

 observations were made before the display 

 opened, during normal hours, and during feed- 

 ing. Because of the possibility of injury leading to 

 mortality, other invasive methods to induce 

 higher speeds were not used. Similar procedures 

 were employed for the smaller sharks. Under- 

 water concussions, induced by dropping heavy 

 objects (fluid-filled metal kegs), and visual stim- 

 uli were used to induce higher speeds in these 

 sharks. Tactile stimuli were also employed to 

 generate a range of speeds in the rectangular 

 tank. 



Video tape was analyzed "frame-by-frame," 

 using manual advance to resolve movements to 

 within 1/60 s (17 ms). Because a large length 

 range was used, kinematic observations were 

 normalized, for convenience, with respect to 

 total length, L, measured from the tip of the nose 

 to the tip of the tail. Specific swimming speed 

 (speed/L), specific amplitude (amplitude/L), 

 and tail-beat frequency (/) were measured for 

 periods of steady swimming of two or more tail 

 beats. The speed of the propulsive wave (c) was 

 calculated from the backward displacement of 

 wave crests, and specific wave-length (k/L) was 

 calculated from e/Lf. 



RESULTS 



Representative swimming movements for 

 three of the species of sharks are illustrated in 



Figure 2. The body was bent into a wave that 

 travelled backwards over the body at a speed 

 greater than the swimming speed. The ampli- 

 tude increased caudally to reach maximum val- 

 ues at the trailing edge (the tip of the caudal fin). 

 In general, the form of propulsive movements 

 was similar to that of other fish, as originally 

 described by Gray (1933). 



Kinematic parameters varied among the six 

 species and with swimming speed. In practice, it 

 proved extremely difficult to induce the sharks 

 to swim over a wide speed range. This is consis- 

 tent with experiences of Johnson (1970) with the 

 brown shark, Carcharhinus plumbeus{= C. mil- 

 berti), and Brett and Blackburn (1978) with the 

 spiny dogfish, Squalus acanthias. Hunter and 

 Zweifel (1971) reported kinematic data for a sin- 

 gle leopard shark, Triakis henlei, swimming in 

 a water tunnel, but the speed range is not given. 

 Only the blacktip sharks swam over a speed 

 range large enough to permit examination of the 

 relationships between kinematics and speed. 

 Data for the other species was therefore simply 

 averaged (Table 1 ). The sharks also did not swim 

 at very low speeds. 



Tail-beat frequency increased linearly with 

 speed (Fig. 3 A), as found for other species of 

 sharks and for teleosts (see Johnson 1970; Hunter 

 and Zweifel 1971; Webb 1975; Aleyev 1977). How- 

 ever, frequencies increased at a higher rate with 

 speed than observed for other fish. Mean specific 

 speeds and tail-beat frequencies varied among 

 the six species of sharks. Compared with the 

 slope of the blacktip shark relationship, more 

 elongate species (e.g., nurse shark; group 3 of 

 Thomson and Simanek 1977) tended to have high- 

 er tail-beat frequencies at a given specific speed 

 than more fusiform fish (e.g., bull shark; group 2 

 of Thomson and Simanek 1977) (Fig. 3B; Table 1 ). 



Specific amplitude of the blacktip shark de- 

 creased with increasing speed (Fig. 3C) and 

 hence was inversely related to tail-beat fre- 

 quency. Specific amplitudes varied from 0.06 to 

 0.21 among species, with the more fusiform 

 sharks having lower values (Fig. 3D). With the 

 exception of the bull shark, mean specific swim- 

 ming speeds were greater for the more fusiform 

 species. Thus, for the interspecific data, specific 

 amplitude decreased with specific speed, similar 

 to the intraspecific observations on blacktip 

 sharks. Among teleosts, both tail-beat amplitude 

 and frequency may increase together at very low 

 speeds (Bainbridge 1958; Webb 1971, 1973). 

 However, over most of the speed range, caudal 



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