STUDY OF FREE-RANGING SHARKS 



453 



suffices for trackings using one-channel transmitters. Multichannel data can 

 also be field decoded in this manner if they are slow-multiplexed (Figure 5). 

 Manual timing, however, is adequate only for pulse rates that are relatively 

 slowly changing and cannot be used to measure rapid-multiplexed data or 

 other kinds of rapidly changing pulse rates. A storage oscilloscope or record- 

 ing paper oscillograph can be used to decode these kinds of data in the field. 

 The full potential of multichannel telemetry is realized only with rapid 

 multiplexing, continuous tape recording of data, and subsequent computer 

 reduction and analysis. The CSULB multichannel system was designed to 

 detect brief, infrequent behavioral events as well as longer term changes. 

 With all eight transmitter channels sampled within about 2 s (1 s if four 

 channels used), even relatively brief events show up clearly in the data. For 

 events likely to have durations of less than 1 or 2 s, the sensor should have a 

 certain degree of "persistence" (see section on sensors). 



Computer Processing— In the CSULB system, data from the receiver 

 are first conditioned by pulse-amplitude and length-discriminating circuitry 

 for initial noise rejection (Figure 20). The resulting uniform pulses are re- 

 corded, along with coded time-of-day information, at slow tape speed on an 

 analog instrumentation recorder. Later these tapes are played at much higher 



Figure 20 Apparatus for field recording of multichannel telemetry data prior to 

 computer processing. The analog instrumentation recorder is fed from the pulse 

 conditioner (black box). The telephone dial is for manual placement of time-of-day code 

 on the tape (decimal code). 



