During most of the work the apparatus was installed as 

 indicated in figure 17o In attempting to discover if tuna pro- 

 duced any soundj the hydrophones of either the OAY, CXJP-l, or 

 NEL apparatus were suspended 18 inches below the surface of the 

 water near the middle of the tank (about 17 feet from the end), 

 or 17 feet from the inner (unscreened) gate ports at the seaward 

 end of the pondo Sounds in the water were thus detected, anpli- 

 fied, and heard using either earphones or a loud speaker. In 

 attempting to discover if tuna responded to sound stimuli, the 

 transducer of the OCP-1 (a hydrophone used as a transmitter) and 

 of the P-H apparatus were suspended 18 inches below the siurface 

 of the water at the south end of the tank, or at the inner gate 

 ports of the pond. The reactions of tima were noted and recorded 

 under control and experimental conditions o 



SOUND PRODUCnON BY TUNA 



Procedure 



Using one or another of the three hydrophone"-amplifier sys- 

 tems, over 100 hours were spent in listening to noises emanating 

 from the tank and pond, and in attempting to ascertain their 

 causes Because of the possibility of sound production from tuna 

 occurring at some hours and not at others, the observations were 

 spaced to cover all hours of the day and nighto 



Results 



In the tank the hydrophones of the NEL and OAT equipment 

 picked up many sounds, but two were distinctly noticeable over 

 the background noise,, One sounded like the snapping of a dry 

 twig and the other was complex^ somewhat like that coming from a 

 beaker of violently boiling water. 



The snapping sound was identified as that of shrimpso This 

 was established Ly bringing the hydrophone near a group of shriisps 

 hiding behind one of the comer baffieso The conplex sound was 

 for a time thought to be coming from either the tuna or liie 

 maninio It was later determined that this sound,, and the other 

 background noises, were caused by the water pun?)ing and tank 

 overflow systems. 



During one of the night observations, when one yellowfm was 

 present in the tank, three distinctly different sounds were 

 heard. One was a very low frequency so\and of very short duration 

 sounding somewhat like a window rattling in the windo The second 

 sounded like water suddenly stirred with a stick The third 

 sounded like a stick being dragged over a piece of sheet metal „ 



60 



