470 



MECHANICAL AND ACOUSTICAL SENSES 



(tilt switch) may be incorporated to activate the radio when the package 

 detaches from the shark and assumes an upright position. 



The transmitter housing includes an accurate digital timer and release 

 circuit that detaches the unit from the shark (Figure 19). At the predeter- 

 mined time, an SCR switch closes, and battery current flows through the 

 breakaway wire, deplating it to the breaking point within a minute or so. 

 Upon link breakage, the package separates from its expendable baseplate, 

 unfolds a counterweight arm, and floats to the surface where it maintains 

 an upright position with the antenna vertical (Figure 23). 



An additional use for this radio system is to ensure recovery of ultrasonic 

 telemetry packages in case sonic contact is lost during tracking. A timed- 

 release, multichannel UST fitted with a radio beacon is shown in Figure 24. 



Data recording— Although the radio units previously described are 

 location-only transmitters, devices may be included in the recoverable pack- 

 ages which would record sensor data during the entire period between attach- 

 ment and release, e.g., depths vs time. See previous section on data storage 

 transmitters. 



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Figure 24 A multichannel ultrasonic transmitter (twin-tube 

 type) fitted with a radio beacon to facilitate location after 

 detachment from a shark. Demonstrated attached to the dorsal 

 fin of a 2.2-m white shark. 



