600 ECOLOGY AND BEHAVIOR 



the fishermen than an added attraction for the sharks. A consideration that 

 might be worthy of ethnographic study is the extent to which (if at all) the 

 rituals of shark fishing serve to transmit and assure the most effective use of 

 procedures developed over many generations. Such cultural traditions would 

 obviously confer major benefits to the local society, but they have not yet 

 been adequately studied. 



Repulsion of Sharks by Sound— Although underwater sounds are 

 used most commonly, by far, to attract sharks, there are a few instances and 

 conditions in which sharks are reported to be repelled by sound. The evi- 

 dence is fragmentary, but it is all the more interesting because experimental 

 studies with controlled auditory stimuli have failed thus far to find a re- 

 producible method for repelling sharks by sounds. 



In Fiji, when netting fish ("busa") swimming near the surface, men dive 

 around the net to watch it underwater. Quite commonly, there are sharks 

 around them. (The shark species could not be identified from descriptions, 

 but lengths of 4 or 5 ft are said to be most common.) The divers knock two 

 oarlocks together underwater to scare the sharks away— a method said to be 

 very effective. 



This procedure has been used for a long time, in Fiji at least, for it is 

 reported that in earlier times stones rather than oarlocks were used for the 

 same purpose. The phrase "giria vata na roloka" ("ring together the stones") 

 is used to describe the method (Gatty 1978). 



Safety and Recognition of Shark Sounds— Safety precautions of 

 Pacific islanders include obvious consideration of the effects of acoustic 

 stimulation upon sharks. As noted above, fishermen use a variety of sounds, 

 even the sound of their own swimming, to lure sharks closer. Divers, on the 

 other hand, usually wish to avoid sharks, and hence try not to splash at the 

 surface. For example, Gilbertese divers are trained to slide into the water, 

 never to jump from their boats (Gatty 1978). Interestingly enough, despite 

 the recognition of the sensitivity of sharks to surface splashes, this safety 

 consideration has not been explicitly publicized among Western divers (e.g., 

 Gilbert 1963). 



One of the most remarkable achievements of divers in some parts of the 

 southwestern Pacific is their recognition of certain species of sharks, and 

 certain activity patterns of sharks, from underwater auditory cues. Expert 

 divers among the Gilbert Islanders claim to recognize at least three different 

 species of sharks from their characteristic swimming sounds. The tiger shark 

 (Galeocerdo cuvieri) is considered "easiest" to recognize, but the identities 

 of the other two were not clear from the descriptions. Gatty (1978), who 

 has spent much time underwater with Gilbertese divers, confirms that the 

 "throbbing" sound produced by tail motions of some large sharks can be 

 differentiated from ambient hydrodynamic sounds, but that these distinc- 

 tions were not clear to him until pointed out by the Gilbertese. 



In the same area, divers report that they can recognize two activity pat- 

 terns of large sharks by the characteristic swimming sounds. "Voyaging" 

 swimming is differentiated from "cruising, investigating, or hunting." The 



