Certain low frequency sounds were produced by the sudden 

 movement of the yellcwfin's tail below and at the surface of 

 the waterc No sounds emanating from either yellowfin or 

 tunny were detected over a frequency range of 1 to 70 kilo- 

 cycles per secondo 



RESPONSE OF TUNA TO SOUND STIMULI 



Procedure 



It was planned to investigate the reaction of tuna to 

 Cl) steady sound of various frequencies^ (2) interrupted sound 

 of various frequencies j, and (3) complex sounds of short dura- 

 tion. Unfortunately J difficulties with the equipment and the 

 eventual death of the experimental fish^ prevented the program 

 ftom being corapleted„ Such observations as were made pertain 

 to Cl)? onlyo 



The experiments were started in the concrete tank, and 

 were later removed to the pond„ For stimuli over the super- 

 sonic range g the OCP-1 equipment was used in the concrete 

 tanko For stimuli at lower frequencies, the P-H equipment was 

 used in both the concrete tank and the pondo 



In the latter experiments., the N3L hydrophone was also 

 used at a fixed distance (17 feet) from the transducer o This 

 distance 3, half the length of the tank, was maintained when 

 the experiments were performed in the pondo The 60-watt 

 anplifier of the P-H equipment was adjusted until the sound 

 became audible at this distance^ 



To enable any reactions of the tuna to be measured in a 

 roughly quantitative manner, the time which the fish spent in 

 Areas S (sound) and Q (quiet) was recorded under control and 

 experimental couditionso The areas are indicated m figure 17o 

 The sound stimulus was audible (through the hydrophone -ampli- 

 fier system) in all parts of Area S, but not in Area Q, except 

 near the boundary o It was assumed that the tuna„ if attracted 

 or repelled by a sound, would spend relatively more or less 

 time in area S than when there was no sound stimulus. 



In the tank, under control conditions, the times spent by 

 the tuna in Areas S and (J should be equal „ However, in the 

 pond under control conditions, the time spent in Area Q would 

 be much longer than that spent in Area S because of the rela- 

 tively greater size of the former area and because, normally 

 the tuna circles the pond turning at the west end within Area 

 S, and turning at the east end at varying distances within 

 Area (Jo 



63 



