402 MECHANICAL AND ACOUSTICAL SENSES 



more attractive than a third signal with 5 pulses/s, but whose pulses were 

 also 50 ms (i.e., 250 ms of energy). 



Behavior of Sharks Subsequent to Attraction 



As an ethologist, I am pleased that attraction studies have provided knowl- 

 edge in areas other than that concerned simply with the acoustical factors 

 underlying attraction per se. Acoustic attraction has provided an excellent 

 background for studying the behavioral activities of various species of sharks 

 in their natural environments; in most cases, the only environment where 

 that is possible, based on present inability to maintain the animals under 

 conditions appropriate for their health or for observation (Gruber and 

 Myrberg 1977; Myrberg, 1976). Although each field observation may be 

 brief, the knowledge gained over many periods can aid, for example, in 

 placing appropriate laboratory findings in reasonable perspective (Banner 

 1972, Evans and Gilbert 1971). Acoustic attraction also reduces dependence 

 on fortuitous encounters with sharks or on situations that often involve in- 

 tense feeding activities (e.g., when food is used to attract animals). Such 

 situations often result in rapid movements by sharks and preclude either 

 the observation or the occurrence of numerous behavior patterns exhibited 

 under less highly motivated conditions. 



Although the behavioral activities noted during sonic attraction must be 

 associated with that context, such activities often relate to other contexts. 

 For example, the final approach to a loudspeaker may result in sharks 

 striking, biting, and even swallowing the entire apparatus (Banner 1968, 

 Myrberg et al. 1969, Nelson and Johnson 1972). This clearly suggests that 

 such animals need not perceive chemically or visually a familiar (food?) 

 object before attacking. This contrasts with earlier claims that complete 

 feeding patterns are elicited only in the presence of complimentary stimuli 

 involving different sensory modalities. Also, specific motor patterns that 

 have been performed by various species of sharks during encounters with 

 man, e.g., "hunching" (Johnson and Nelson 1973, Myrberg and Gruber 

 1974), have been noted several times directly in front of a transducer at the 

 end of a rapid approach (Nelson and Johnson 1972). 



These quite differing contexts, as well as others with similar patterns, 

 appear to possess one common feature— the condition favoring conflict 

 between the tendencies of approach and withdrawal. The apparent result is 

 hesitance in carrying out either activity. This suggests that "hunching" may 

 be an expression movement rather than a ritualized social display that is 

 released only by a specific stimulus (configuration). These few examples 

 point out how observations may lead either to better understanding of the 

 probable reasons for the occurrence of specific activities or, at least, to 

 predicting and possibly even controlling the behavior of these predators. 



Many species-typical action patterns by a variety of sharks have been ob- 

 served in the vicinity of a sound source. Many of these patterns have been 

 described by Myrberg and Gruber (1974); the rest are explained in the actual 

 accounts (Banner 1968, 1972; Myrberg et al. 1969, 1972, 1975a; Nelson and 



