male bonnetheads accelerated from a position just 

 above and behind a large female and scraped her 

 dorsum between the first and second dorsal fins 

 with their heads, often leaving similar scrapes 

 (Myrberg and Gruber 1974). Bite scars, often 

 consisting of a row of teeth marks, are inflicted 

 during courtship in some sharks (Stevens 1974; 

 Klimley 1980). The presence of these scarred 

 females raises the possibility that the scalloped 

 hammerhead schools may have a reproductive 

 function. Grouping for reproduction has been 

 speculated for Galeorhinus australis (Olsen 1954) 

 and Squolus aca?ithias (Jensen 1965). 



Other functional possibilities for the schooling 

 include: 1) migration I Olsen 1954; Kenney 1968), 

 2) protection from predation (Barlow 1974), and 3) 

 cooperative location or capture of prey (Coles 1915; 

 Bigelow and Schroeder 1948). Other than the 

 departure of tagged sharks from El Bajo, little 

 evidence for or against the first hypothesis can 

 be marshalled. The second hypothesis seems un- 

 likely due to the absence of known predators. We 

 do, however, have some evidence against the last 

 hypothesis. Feeding was not observed, although 

 scalloped hammerheads were often swimming 

 through large schools of fishes. No feeding re- 

 sponses were directed at baits placed either among 

 or above large numbers of scalloped hammer- 

 heads. Although fishing was carried out contin- 

 uously, only a single male was captured. Feeding 

 readiness was also tested by playing back sounds, 

 attractive to many species of sharks including 

 Sphryna sp. (Nelson and Johnson 1972), and 

 baiting immediately after encountering grouped 

 sharks. In 20 min of sound playback and 125 min 

 of baiting, only a single shark was attracted. 

 The phenomenon of grouped hammerhead sharks 

 presents a unique opportunity for the further 

 understanding of shark social behavior, since 

 the sharks are found in sufficiently clear water 

 for observation, shallow enough for free diving, 

 remain in a sufficiently limited area for prolonged 

 observations, and tolerate the approach of divers. 



Acknowledgments 



The authors thank J. McKibben, G. Pittenger, 

 T. Rulison, and J. Sullivan for assistance in data 

 acquisition. Flip Nicklin organized the cruise with 

 financial support from National Geographic Mag- 

 azine. The Juan de Dios Batiz, a research ves- 

 sel of the Centro Interdisciplinario de Ciencias 

 Marinas, La Paz, was kindly made available for 



the study by the director, D. Lluch Belda. Photo- 

 graphs in Figure 2 were taken by Jim McKibbn, 

 F. Nicklin, and D. Nelson. Partial support was 

 provided by ONR contract N00014-77-C-0113 to 

 the second author. 



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