loudspeaker produces audible signals which 

 aid in the interpretation of the returning 

 echoes. The signal -level indicator shows 

 the strength of the soundwaves being trans- 

 mitted by the sonic tag on the fish and in- 

 dicates very roughly the distance of the fish 

 from the echo -ranging system. An automatic 

 tracking receiver is shown installed in a Fish 

 and Wildlife Service boat in Fig. 3 . 



Portable Receiver 



Since it is not possible to use the auto- 

 matic tracking receiver in confined conditions 

 such as a fishway pool, a small portable bat- 

 tery operated receiver was designed to detect 

 the presence of a fish with a sonic tag attached 

 in restricted well-defined areas. This re- 

 ceiver was designed for use with a non- 

 directional listening hydrophone. The hydro- 

 phone in the water picks up the sound waves 

 transmitted by a sonic tag and amplifies them 

 through a loudspeaker in the receiver. Ear- 

 phones can be used when necessary to reduce 

 the interference of outside noises with the 

 signals from the sonic tag. Figure 4 shows 

 a portable receiver and listening hydrophone. 



ATTACHMENT OF TRANSDUCER 



A method of attaching the sonic tag to an 

 adult salmon was developed to minimize the 

 effect of the tag on the natural movements of 

 the fish. With this technique the tag is at- 

 tached to a fish underwater, without handling 

 the fish and without immobilizing it. 



Materials and Methods 



The transducer is attached to a fish by a 

 "hog-ring", 1-1/4-inches wide and 1/2 -inch 

 high, fabricated from nickel chromium wire 

 .064 inches in diameter, the ends of which 

 are beveled to a sharp edge . To make a 

 rigid connection with the sonic tag, the ring 

 is first centered in a hole in a brass rivet 

 and silver -soldered in place. The head of 



the rivet is then brazed to the outside of 

 the tag with aluminum solder . A sonic 

 tag with "hog-ring" is shown in Fig. 5. 



The tag is attached with special pliers 

 to an adult salmon while it remains in the 

 water. The salmon is led into a trap four 

 feet square, which contains 1-1/2 feet of 

 water. When the activity of the fish de- 

 creases and it maintains a constant position 

 in the trap, the tag is gently placed on the 

 back of the fish two inches behind the dorsal 

 fin and clinched shut in the flesh. This 

 procedure eliminates the necessity of 

 handling the fish with seines or dip" nets and 

 of manually holding the fish during the tag- 

 ging operation. The salmon is released 

 within 30 seconds after tagging and its 

 movements are followed with the receiving 

 equipment . The manner in which the sonic 

 tag is held by the pliers for attaching to a 

 fish is shown in Fig. 6. 



Effect on Natural Behavior 



In order to interpret data obtained with 

 the sonic, equipment it was necessary to 

 determine the effect of the tag on the natural 

 movements of adult salmon. Experiments 

 were conducted in a hatchery holding pond 

 located in a small stream where large 

 numbers of fish were trapped and held for 

 spawning purposes. The pond was 100 yards 

 long, 50 yards wide and averaged 3 .5 feet 

 deep. A rack at the upstream end of the 

 pond created an even flow of water the 

 velocity of which was estimated at one -half 

 foot per second. 



Sonic tags were attached to adult chinook 

 (O. tshawytscha ) and silver (O. kisutch) 

 salmon ranging in length from 1.5 to 2.5 

 feet which were released into the holding 

 pond. Fish which were active and not ready 

 for spawning were selected for tagging. 

 These fish were removed from a seine used 

 by hatchery personnel to obtain fish for 



