STUDY OF FREE-RANGING SHARKS 



445 



Figure 16 Body-position sensor for measuring jaw 

 angle: (a) Rods sutured to skin, (b) Housing (attached to 

 case of rotary trimpot). (c) O-ring-sealed shaft (attached 

 to rotor of trimpot). (d) Cable to transmitter. 



events such as heartbeats could be telemetered by pulsed transmission at 

 long ranges. The main ECG spike as picked up by electrodes could directly 

 trigger the production of a standard ultrasonic pulse thereby making trans- 

 mitter pulse rate a direct duplication of heart rate. 



Of special interest in shark behavior is the telemetry of pH or temperature 

 from a stomach-implanted transmitter. Such data, in addition to its physio- 

 logical implications, could provide indications of individual feeding events. 

 When a piece of food and accompanying ocean water are swallowed, there 

 should be a noticeable change in stomach pH and a possible change in 

 stomach temperature, the latter especially in "warm-bodied" species. 



Nonresistive Sensors— The sensors just described that were designed 

 for use in the CSULB shark transmitters act as variable resistors, i.e., bulk 

 resistors, passing current in either direction. The transmitter circuit was 

 originally designed to use this type of sensor because, in multichannel ap- 

 plications, it is easier to multiplex sensors if they are all of one type. Since 

 some desired sensors were already resistive types (thermistors, photocells), it 

 was logical for the rest to be resistive. 



