STUDY OF FREE-RANGING SHARKS 447 



For short-term trackings (hours, days) it seems best to use attachment 

 methods that minimize initial trauma. Two proven methods usable on un- 

 captured, free-swimming sharks are (1) external, via a barbed dart thrust in 

 by an applicator pole, and (2) internal, by inducing the shark to swallow the 

 transmitter concealed in bait. The latter method is totally atraumatic and 

 does not appear to affect the shark's behavior at all. The former method 

 usually results in the shark dashing away after being tagged. In the case of 

 externally tagged blue sharks, however, normal behavior appeared to return 

 within 60 to 90 min (Sciarrotta 1974). Some individuals seemed almost 

 unaffected, circling back to the bait canister within seconds after applica- 

 tion (Figure 1). On the other hand, some sharks captured and tagged after 

 much struggling showed probably traumatic effects for many hours after 

 release. 



For longer term (weeks, months) studies it may be better to capture the 

 shark and carefully attach the transmitter to its skin or fin in a way that 

 minimizes longer term irritation. Stomach implantation eliminates irritation 

 but expected lengths of retention are not yet well enough known, e.g., some 

 sharks have regurgitated USTs within the first few days, another individual at 

 10 days. For long-term trackings the best method might be insertion of the 

 transmitter in the body cavity via an abdominal incision. 



Tracking— Tracking operations normally begin immediately after the 

 unit is applied to the shark and are maintained either continuously or inter- 

 mittently until the end of the mission, at which time an attempt is some- 

 times made to recover the transmitter. The signal is detected using one of 

 several tunable, narrow-band receivers, some of which are waterproof and 

 designed for use in wet weather or by divers under water (Figure 18). When 

 tracking from a small boat, the operator maintains signal contact using a 

 directional hydrophone, the simplest method being manually holding the 

 staff-mounted unit over the side of the drifting boat. It is much preferred, 

 however, to utilize a streamlined gunwale or bow mount for the hydro- 

 phone, as described by Stasko (1976), Stasko and Polar (1973), and Lawson 

 and Carey (1972), which permits reception while the boat is under way at 

 moderate speeds. 



When reception is good (strong signal, low noise) an omnidirectional 

 hydrophone can be used to maintain signal contact; this gives the trackers a 

 rest from the tedium of manually maintaining proper aim of the directional 

 hydrophone. When signal strength becomes marginal, its direction is deter- 

 mined and the boat moved closer and again allowed to drift. Locations of 

 the shark are plotted, and the telemetered data is stopwatch decoded or tape 

 recorded for later computer reduction. 



If the shark's location is determined relative to the boat, then the boat's 

 location must be determined in order to plot the shark's true position. 

 During the day, standard visual positioning methods usually suffice, using 

 shoreline reference marks or special marker buoys deployed for this purpose. 

 The primary problem occurs at night, especially in remote areas without 

 lighted landmarks. Small-boat radar is one answer, if the shorelines are of 



