FISHERY BULLETIN: VOL. 74, NO. 1 



Figure 3. — Buoy deployed with detection and recovery gear. 



180° 



Figure 4. — Typical signal level as function of aspect angle 

 for a single fish. 



Storage was therefore limited to include data 

 from a maximum of seven fish. The number offish 

 counted per sample and depth of each fish (to the 

 nearest meter) are stored in a serial shift register 

 memory, as are data on buoy identification and a 

 data synchronization code. These data are stored 

 in a format which makes telemetry noise and 

 false counts easily recognizable and therefore 

 easy to eliminate. 



After all data from one acoustic pulse are 

 gathered and stored they are automatically 



shifted through the telemetry system for trans- 

 mission to the monitoring ship. Frequency-shift- 

 keying (FSK) through the audio inputs of com- 

 mercially available transceivers is currently 

 used. The frequency response of the audio chan- 

 nels limits the bit rate to 100 Hz. A reliable te- 

 lemetry range of 15 km in fairly rough seas has 

 been achieved using this technique. A 6-MHz 

 telemetry system has been developed which will 

 increase the useful range to 100 km and will 

 allow the use of radio direction finding equipment 

 found aboard most seagoing vessels for buoy 

 recovery. 



In the current configuration, the buoys will 

 operate continuously for 5 days before battery 

 recharging is necessary. The acoustic and logic 

 systems were carefully designed to minimize 

 average power drain. COSMOS elements were 

 used in logic design, and transmitter and receiver 

 standby current is very low. Battery life is there- 

 fore limited by the telemetry system. The rela- 

 tively low data rate requires that the transmitter 

 be on for 0.6 s/sample. However, the redesigned 

 telemetry system can increase data rate by an 

 order of magnitude which will increase buoy life 

 between charges to more than 6 wk. 



The shipboard system consists of a telemetry 

 receiver, a data synchronizer with buffer storage, 

 a printer, and a digital tape recorder. Data from 

 up to 10 buoys can be received and processed at 

 the monitoring ship. Real time readout is pro- 

 vided by the printer. The digital tape recorder 

 provides data storage for later computer analysis. 



FIELD OPERATIONS AND RESULTS 



The acoustic buoy system has been operated in 

 the Adak area during the summers of 1972, 1973, 

 and 1974. The 1972 operation suggested sig- 

 nificant design changes in the electroacoustic 

 portion of the system. These modifications were 

 accomplished during the winter of 1972-73. The 

 results of the 1973 operation indicated that spe- 

 cial attention had to be given to system sensitiv- 

 ity and field calibration which was done prior to 

 the start of the 1974 field season. The present 

 configuration represents an essentially final de- 

 sign with only minor modifications to be made in 

 the future. 



Whenever feasible, the acoustic buoys have 

 been operated at the same station and at the 

 same time as the purse seine in order to obtain 

 comparable data. This was not always possible. 



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