Later, day and night observations showed that these sounds 

 were caused by tuna in the following manners 



(1) The low frequency sound of very short duration was 

 caused by the sudden movement of the tail of the yellcwfino 

 \Bien getting underway^ the first one or two movemsits of the 

 tail created enough pressure in the water to produce sound 

 waves which were picked up by the hydrophone,, Vfhether this has 

 any biological sigiificance from the point of view7schooling is 

 a matter of conjecture,, Certainly^ in the large pondj the 

 speed undergoes sudden chai.ges while the tuna is swimming its 

 lengthy and this is also likely to occur in the open seao It 

 further suggests the possibility that tuna may react to sound of 

 very low frequencyo 



(2) The second sound was produced when part of the tuna's 

 tail came above the siorface of the water^ As occasionally tuna 

 are observed to jump and play at the surface, this sound may also 

 be produced in the natural habitats 



C3) The third sound was produced when the tuna accidentally 

 rubbed against the hydrophone o 



No additional sounds were detected when two yellowfin and 

 one tunny were present in the tanko 



During one of the tests, one of the yellowfin suddenly went 

 beserk, and began bumping and scraping itself against the walls 

 of the tanko Ylhen it died, its skin was almost conpletely eroded^ 

 However, even during this period of frantic acti\'ity, no sound 

 of moderate or high frequency range (1 to 10 kilocycles) was 

 heard with the hydrophone in use at the time (OAY) o 



It was decided that a test should be conducted to explore 

 the possibility that tuna might be emitting sound in the super= 

 sonic range o A o-hour trial with the 0CP=1 apparatus gave nega- 

 tive resultso Further trials were not conducted because the 

 apparatus was no longer available o 



The NEL equipment was also used to investigate sound product- 

 ion by tuna in the pondo Many different sounds were heard,, but 

 none could be identified with either the yellowfin or the tunnyo 



Summary 



Over 100 hours were spent in listening to the sounds picked 

 up by the hydrophone placed in the tank and the pond contair mg 

 tunao The listening periods were staggered so that all hours of 

 the day and night were covered o 



62 



