FIGURE 28.-Sonie tag being attached to 7-pound steelhead 

 trout. One capsule contains mercury cell battery and 70-kHz 

 transducer; adjoining capsule houses oscillator circuit com- 

 ponents. Transmitting range is 1 to 2 miles in fresh water, 

 or about 1 mile in salt water. Battery life is 10 weeks. 



FIGURE 29.— A recently developed sonic tag is being inserted 

 through the mouth and esophagus into the stomach of a chinook 

 salmon. The procedure protects the tag and does not harm the 

 salmon because.it does not feed during its upstream migration. 



To observe the effects of dams on upstream migration, 

 more than 3,000 salmon and steelhead trout were tagged 

 with miniature sonic transmitters (fig. 28) at Bonneville 

 and McNary Dams. The sonic "tags," attached to the backs 

 of the fish or inserted in their stomachs (fig. 29), sent out 

 pulsed signals. As the fish moved upstream, the signals were 

 recorded by automatic monitors (fig. 30) along shore and at 

 the mouths of tributaries. Boat crews equipped with portable 

 receivers made weekly surveys. 



FIGURE 30.— Shore monitor which records passage of sonic- 

 tagged fish. Data include date, hour, direction of passage, 

 and repetition of lag pulses. Variations in the latter indicate 

 where and when fish was tagged. Monitor is completely auto- 

 matic; imils need servicing only once every 7 to 10 days. 



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