STUDY OF FREE-RANGING SHARKS 477 



speed increase" (speed sensor) might turn out to be an event representing 

 a shark chasing a certain type of prey. A different event might consist of 

 "tight circling, slow speed" at a different depth, and this might indicate 

 feeding on some other prey. Specific events of these types, even though they 

 may occur only briefly and infrequently, would be readily apparent on 

 computer printouts of continuously recorded data. 



Courtship and Mating— While little is known about natural feeding 

 behavior in sharks, even less is known about social behaviors such as court- 

 ship and mating. Courtship in sharks has never been described and even 

 copulation itself has been illustrated in the literature only from aquarium 

 observations of two small, bottom -dwelling species. For the large active 

 species, almost nothing is known of mating, except for what can be in- 

 directly inferred from evidences such as mating scars (tooth marks) on 

 females or sperm in the claspers of males. Questions as to where, when, 

 and how often mating occurs in the natural environment remain com- 

 pletely unanswered. It is intriguing to consider the possibility of approach- 

 ing these questions with telemetry. 



One way would be to search for some specific event believed associated 

 with mating, such as flexing of the claspers. At the beginning of the sus- 

 pected season of mating, mature males would be captured and fitted with 

 long-term memory transmitters with sensors to detect clasper flexion. 

 Data storage (as opposed to continuous tracking) would seem the most 

 feasible initial technique, since the researchers would have very little idea 

 of when or how often to expect the clasper events. The various units would 

 be relocated and interrogated at intervals, e.g., daily, perhaps only weekly. 

 When clasper activity was indicated, a shorter term memory might be used 

 to determine more accurately the time and place of the behavior. It would 

 then be feasible to begin continuous trackings to obtain the most detailed 

 telemetry account of the behavior. If conditions warranted, attempts at 

 direct observation of the behavior might be made then by receiver-equipped 

 personnel using scuba or submersibles. 



Physiological Monitoring 



A good example of the use of acoustic telemetry for monitoring physio- 

 logical responses in free-ranging marine animals is the work of Carey and 

 Lawson (1973) on thermoregulation in large tunas and sharks. Here the 

 advantage of telemetry was that it allowed the use of the ocean as a 

 "laboratory," making it possible to work on large, fast-swimming species 

 impossible to maintain in existing experimental aquariums. Furthermore, 

 the ocean had the thermal structure necessary for the experiment, which 

 involved determining whether the animals actively regulated body tempera- 

 ture when moving through gradients of water temperature. The experi- 

 menters found that, if necessary, they could induce the animal to dive into 

 colder waters by running the tracking boat directly overhead, as was done 

 with one telemetered dusky shark. 



