ANCHOR 

 PLATE 



RUBBER BAND 



Figure 1. — Ultrasonic transmitter and tagging apparatus, a. Temperature sensing 

 transmitter, b. Anchor plate, c. Rod for applying anchor plate, d. All items as- 

 sembled. 



the fish alongside as quickly as possible. When the 

 fish was alongside the boat, its condition was 

 checked and its size was estimated. If the fish ap- 

 peared to be in good condition, the tag was inserted 

 and the fishing line was cut to release the fish. 



Many of the people of the sportfishing community 

 took an active interest in the tracking project. As a 

 result several fishermen offered to donate their mar- 

 lins. Upon receiving radio communication that a 

 fisherman was willing to donate a hooked marlin. 

 Christel transferred the tag. harpoon, and sometimes 

 a crew member. Tagging operations on the other 

 boats were similar to those aboard Christel. 



Tracking Procedures 



During the catching and tagging operation Charles 



H. Gilbert was positioned 200-300 m away from the 

 fishing boat. Upon release of the fish, the following 

 data were recorded at 5-min intervals: time, ship's 

 heading, relative bearing of the hydrophone, tilt 

 angle of the hydrophone, and pulse rate of the tag. 

 Ship's position was determined and recorded at 

 half-hour intervals. Because of poor signal-to-noise 

 ratios, it was not always possible to measure the 

 pulse rate. Because of a malfunction in the tilt angle 

 indicator during the 1972 operations, the observer 

 was sure of the tilt angle only when the hydrophone 

 was at 0° or 90°. 



The ship was guided to maintain a distance of 

 approximately 800 m from the estimated position of 

 the tagged marlin. Actual distance between ship and 

 fish continually varied from about 400 to 1 ,200 m for 

 the following reasons: (1) the minimum forward 



266 



