376 MECHANICAL AND ACOUSTICAL SENSES 



well covered by Dijkgraaf (1963a) and by some of the authors in Cahn 

 (1967). 



There is now considerable anecdotal evidence that sharks are strongly 

 responsive to disturbances created in the water, but the type of response 

 seems to depend on the shark, the disturbance, and the observer! For ex- 

 ample, some divers (e.g., Eibl-Eibsfeldt and Hass 1959) believe that a loud 

 shout made underwater will deter a shark attack (the "scream theory"); 

 others regard this advice as "little short of criminal" (Cousteau and Cousteau 

 1970) because they believe that sharks will actually be attracted. The fact 

 that sharks are lured by underwater disturbances has been noted for some 

 time and has apparently been exploited by Solomon Island fishermen who 

 attract sharks by creating noises with coconut shells that are said to simulate 

 the clapping sounds made by lobster tails (Coppleston 1962)! The wide- 

 spread observation by divers that sharks respond rapidly to struggling 

 speared fish has resulted in recent attempts to examine the acoustic re- 

 sponses of sharks. This type of research is hampered, however, by the dif- 

 ficult technical problems associated with underwater sound, the large size of 

 the fish involved, and the difficulty of establishing just which is the respon- 

 sive sense organ. Much of this work, which is reviewed in detail elsewhere in 

 this volume can, for present purposes, be summarised as follows: 



1) Studies on sharks housed in small tanks: (Mustelus (Parker 1909); 

 Scyliorhinus (Dijkgraaf 19636); Negaprion (Wisby, Richard, Nelson, and 

 Gruber 1964; Nelson 19676)) 



2) Studies on large sharks in pens (Carcharhinus (Kritzler and Wood 

 1961); Carcharhinus and Sphyrna (Davies, Lochner, and Smith 1963)) 



3) Field studies, by divers or with underwater television systems, made on 

 numerous species (Banner 1968; Richard 1968; Myrberg, Banner, and 

 Richard 1969; Myrberg, Ha, Walewski, and Banbury 1972; Nelson 1967a; 

 Nelson, Johnson, and Waldrop 1969; Nelson and Johnson 1972). 



When taken together, these studies have revealed that sharks respond to 

 low-frequency vibrations (<1000 Hz), which if pulsed can be strongly attrac- 

 tive (see Nelson and Johnson 1972). Such detection can certainly take place 

 over long distances, for Nelson (1969) reports a response by a shark 183 m 

 from a sound source, but as very few of these studies, except for those in 

 group 1, have been combined with nerve or sense organ ablation, it is not 

 possible to designate the responding system. However it should be possible, 

 on the basis of what is known of the lateral line and the ear, to speculate 

 reasonably about the likely roles of each sense organ under field conditions. 



A clearer understanding of the types of disturbance created by an object 

 moving in water has come from the writings of Pumphrey (1950), Harris and 

 van Bergeijk (1962), Harris (1964), and van Bergeijk (1964). An object 

 moving in seawater sets up simultaneously displacement and compression 

 waves. These two disturbances are called near-field sound and far-field sound 

 because the amplitude of the near field declines more, the greater the dis- 

 tance from the source. The near field is the dominant stimulus at distances 



