STUDY OF FREE-RANGING SHARKS 



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Figure 23 A prototype timed-release, radio-float transmitter designed for application 

 to free-swimming sharks. Upper photos: Unit in folded position attached to expendable 

 baseplate, showing breakaway wire and electrode plate. Lower left: After separation from 

 baseplate and unfolding of counterweight arm. Center right: Demonstrated on a 1.7-m 

 blue shark. Lower right: Demonstrated on a 2.2-m white shark. 



vertical fiberglass-covered whip antenna. The unit is set for a rather rapid 

 pulse rate of 4/s to facilitate recognition of the signal under conditions of 

 intermittent reception, e.g., signals blocked when unit is in trough of waves. 

 Length of the continuous-wave (CW) pulses is about 50 ms, and the current 

 drain during the pulse is about 1.5 mA. The 3V, 160-mAh mercury battery 

 will run the unit continuously for about 10 days. For popup times of several 

 days or less, therefore, the radio may be simply turned on prior to applica- 

 tion, remaining on until recovery. For longer durations, a mercury switch 



