FIG. 2 An echogram from the Benmar DR-680 showing indi- 

 vidual targets of 3-in. long coho salmon. Water depth is 8 ft. 



TRANSDUCER 



REDWOOD 

 y' TANK 



Fig. 3 Transducer in test tank showing conical detection 

 volumes of original transducer (shaded) and the Webster wide 

 beam transducer. 



test tank. The transducer was mounted at the bottom 

 of the tank so that as much as possible of the water 

 at the top of the tank could be monitored for fish. 

 The sounder was activated for approximately 2.5 

 min once each hour by an electrical timer. The 

 resulting echograms revealed two distinct depth 

 behavior patterns: 1) during daylight hours the fish 

 were quite active and homogenously distributed 

 below 2 ft, 2) at night the fish concentrated at mid- 

 depth (2 to 6 ft deep) and were inactive. 



Individual targets of fish could have been 

 manually counted to quantify the percentages of 

 fish in specific depth intervals; however, this proved 

 to be difficult because there were approximately 

 300 fish in the test tank. 



COUNTER/PRINTER SYSTEM 



An electronic target echo counter and tape 

 printer system were designed and constructed so 

 that the numbers of fish at specific depth intervals 

 could be quantified and recorded automatically. 

 This system was constructed with standard tran- 

 sistor-transistor-logic gates on printed circuit 

 boards manufactured at the Prescott Facility. The 

 printer used was the Model B5-102 Moduprinter® 

 manufactured by Practical Automation, Inc. 



Two transducers were used with the counter 

 system so that a maximum volume of water inside 

 the tank could be sampled. One transducer was 

 mounted at the bottom of the tank; the other just 

 beneath the water surface. Four detection areas 

 were defined in the intersecting detection cones 

 (Fig. 4). Because the entire volume of the tank is not 

 sampled, all results of the tests are based on the 

 assumption of homogenous horizontal distribution 

 of fish in the tank. 



Basic operation of the counter/printer system 

 is illustrated by the timing diagram in Fig. 5. The 

 instrument can be programmed to generate a trigger 

 pulse once every 5, 10, 20, or 60 min. Whenever 

 this pulse occurs, it turns on the sounder, auto- 

 matically switches to the top transducer, and 

 initiates the control logic for the counting of a 

 sample. Forty sec after this pulse occurs, the con- 

 trol logic activates electronic counters #3 and #4. 

 During a sampling period of 1 sec, all fish echos 



FIG. 4 Detection areas inside the intersecting conical detection 

 volumes. 



Monitoring Vertical Distribution 21 



