TRIGGER PUESE 



SOUNOERON J 



IOP COUNT 



BOTTOM COUNT 



PRINT 



RESET COUNTERS 





10 B 30 » 50 60 



TIW (SECONDS) 



FIG. 5 Basic timing diagram of the electronic counter/printer 

 system. 



detected by the sounder in the lower half of the 

 tank are counted and stored in the counters 

 (Fig. 4). Sixty transmit pulses occur during this 

 sample period; therefore, a single fish in detection 

 area #3 for the sampling period would result in the 

 number 60 being stored in counter #3. Two fish in 

 the area would result in the number 120 being stored 

 in the counter. The sounder transmit pulse width is 

 50 psec. At a velocity of sound in water of 5000 ft/ 

 sec, this represents a distance of 3 in. Therefore, 

 two fish closer together than 3 in. could possibly 

 be detected as a single fish by the sounder. Fifty 

 sec after the trigger pulse, the bottom transducer 

 is automatically switched to the sounder and after 

 a 10-sec delay the second sampling period is used 

 for counting the number of fish echos in detection 

 areas #1 and #2 (Fig. 4). Seventy sec after the trigger 

 pulse the data stored in the counters is printed 

 on the chart paper. The counters are then reset 

 to zero and the sounder and control circuits are 

 turned off. When the next trigger pulse occurs, 

 the sequence is repeated. 



RESULTS OF TANK TESTS 



During 1974, separate tests were conducted 

 continuously for a week to monitor the diel depth 

 behavior of squawfish, smelt, crappie, and cutthroat 

 trout in the test tank. For these tests, the trigger 

 pulse was programmed to count a sample once an 

 hour, day and night. Fish depth data were recorded 

 by the automatic counter/printer system; the task 

 of manually counting fish echos was eliminated. 

 Data from the tapes were tabulated and standardized 

 to compensate for the unequal water volumes of the 

 detection areas (Fig. 4). Although some variation 

 was observed in the results of these tests, all species 

 generally avoided the top 2 ft of the tank and tended 

 to concentrate in the middle areas. The test tank 

 environment is obviously different from that of the 

 river; however, we did not have to contend with the 

 problem of false echos caused by other fish or 

 debris. 



These tests demonstrated that the Benmar® 

 sounder could be used effectively for monitoring 

 the depth of fish in shallow water. 



MONITORING THE VERTICAL DISTRIBU- 

 TION OF FISH IN THE LOWER COLUMBIA 



RIVER 



An attempt to use the sounder from a boat in 

 the river was unsuccessful. The presence of the boat 

 seemed to "spook" the fish and very few were 

 detected. Subsequently an array of 10 transducers, 

 mounted on an aluminum sled (Fig. 6), was placed 

 on the bottom of the river to overcome this problem. 

 An electronic sequencer, with transistor-tran- 

 sistor-logic gates and relays (Fig. 7), was designed 

 to serially switch the sounder output to each trans- 

 ducer. Fig. 8 is a block diagram of this unit. 



FIG. 6 Photograph of the 10-transducer array. 



FIG. 7 The electronic sequencer used with the 10 transducers. 



22 Marshall 



