SWIMMING KINEMATICS OF SHARKS 1 



P. W. Webb- and Raymond S. Keyes 3 



ABSTRACT 



Video-tape recordings were made of locomotor movements of six species of free-swimming sharks. 

 The following kinematic parameters were measured, normalized where appropriate with total body 

 length (L): tail-beat frequency (/), specific tail-beat amplitude (A/L), specific wavelength of the 

 propulsive wave (A/L), specific stride length (S/L), and the rate of change of A/L with position along 

 the body. These parameters were measured over a range of swimming speeds up to 3.9 m/s (4 L/s) for 

 one species, the blacktip shark, Carcharhinus melanopterus. Data were obtained only over a narrow- 

 range of low swimming speeds for the other species, because they could not be induced to swim at 

 high speeds. For the blacktip shark, /increased with speed, but A/L, A/L, and, hence, S/L all de- 

 creased as speed increased. Among the six species, A/Land S/L tended to be larger for more fusiform 

 species, while A/L and /, at a given speed, appeared to be lower. This implies swimming move- 

 ments of more fusiform species generated more thrust per beat than elongate species and/or the 

 swimming drag was lower. The pattern of amplitude changes along the body length of sharks was 

 intermediate between that observed for elongate and fusiform teleosts. 



Thrust and swimming efficiency can be improved when discrete fins interact, as between the 

 dorsal and caudal fins of sharks. For this to occur, a phase difference of >0.5 n must occur between 

 the vortex wake shed at the trailing edge of an anterior fin and the leading edge motion of a more 

 posterior fin, which interacts with the upstream vortex sheet. The variations in swimming kine- 

 matics with speed, the differences among the species studied, and the conservative nature of body 

 form in sharks probably function to increase thrust and efficiency by such interaction between 

 median fins. 



Most studies on fish locomotion have concen- 

 trated on bony fish, especially teleosts. As a re- 

 sult, modern ideas on fish locomotor functional- 

 morphology are dominated by knowledge of only 

 one of the major groups of fish. However, there 

 are many unique features among cartilaginous 

 fish that suggest they have exploited some differ- 

 ent biomechanical possibilities. Sharks appear 

 to swim like elongate teleosts, but in contrast 

 they have discrete, often widely spaced median 

 fins more typical of fusiform teleosts. Lighthill 

 (1970) and Sparenberg and Wiersma( 1975) have 

 shown that this combination provides an oppor- 

 tunity for median fins to interact in such a way 

 that thrust and Froude efficiency (the ratio of 

 useful work to total work of the propellor system) 

 are improved. 



If shark locomotion were to utilize flow inter- 

 actions between median fins to hydromechanical 

 advantage, they would have to swim somewhat 

 differently from teleosts. For example, teleosts 



'Contribution No. 8104-SD from Sea World, San Diego, Calif. 



2 Southwest Fisheries Center La Jolla Laboratory, National 

 Marine Fisheries Service, NOAA, La Jolla, Calif.; present 

 address: School of Natural Resources, University of Michigan, 

 Ann Arbor, MI 48109. 



3 Sea World, San Diego, CA 92109. 



modulate tail-beat frequency with speed, but 

 sharks might also have to vary other kinematic 

 parameters, such as the length of the propulsive 

 wave and tail-beat amplitude. Therefore, the fol- 

 lowing experiments were performed to deter- 

 mine how swimming kinematics and phase dif- 

 ferences between fin motions varied with speed 

 for six species of sharks. While difficulties were 

 encountered in obtaining data over a wide range 

 of speeds, the results suggest that sharks vary 

 swimming kinematics to utilize interactions be- 

 tween median fins, as postulated by Lighthill 

 (1970). 



METHODS 



Observations were made on six species of free- 

 swimming sharks (Fig. 1). Three species, the 

 bull shark, Carcharhinus leucas; lemon shark, 

 Negaprion brevirostris; and nurse shark, Gingly- 

 mostoma cirratum, were approximately 2-2.5 m 

 in total length. They were contained in the public 

 display at Sea World, San Diego, Calif., described 

 by Weihs et al. (1981). Specimens of the other 

 three species were smaller; Pacific blacktip 

 shark, Carcharhinus melanopterus (total length, 

 L = 0.97±0.5 m; X ± 2SE; N = 7); bonnethead, 



Manuscript accepted February 1982. 

 FISHERY BULLETIN: VOL. 80, NO. 4. 



1982. 



803 



