Table 2. — Energy levels measured at the horizontal and vertical center 

 of the tank compartments at selected frequencies. (Cont'd.) 



Dvnes per cm.'^ 



**Decibels, with reference to the lowest reading, 25 dynes per cm. "^ calculated 

 by the formula Db = 10 Iogp2 where P^ is the reference level in Dynes per cm.^ 



and P2 is the level to be compared. 

 ***Produced by piezoelectric transducer; all other frequencies were produced by 

 the electromagnetic transducer. 



The results of the laboratory phase of 

 the research were not encouraging. There 

 was no indication that the sound waves either 

 attracted or repelled the young salmon. In 

 view of the fact that the experimental tank had 

 demonstrated definite limitations, we were 

 hopeful that the move into Lake Washington 

 would produce more promising results. 



RESULTS OF OPEN-WATER 

 TESTING 



Open -water testing in Lake Washington 

 covered the range of sound from 5 c .p. s. 

 through 20, 000 c.p.s. (table 1), and more than 

 23, 500 young silver salmon were tested while 

 covering this range. As we were aware of the 

 limitations of testing in the laboratory tank, we 

 felt it advisable to cover the entire range of 

 sound as originally planned. 



During the entire testing of the range 

 from 5 to 20, 000 c.p.s., there was never 

 any indication that the sound was either at- 

 tracting or repelling the fish. As in the 

 laboratory, fish responded to the sound with 

 the typical "start" reaction. This response 

 was more pronounced in the lower frequencies 

 than in the higher. When tests had reached 

 the level of approximately 15, 000 c.p. s. 



there was a noticeable decrease in the 

 " start" , and by the time 20, 000 c.p.s. 

 was reached it was seldom evident. Re- 

 sults of a typical open -water test are 

 shown in figure 10 . ' 



After studying the waters and the 

 natural noises contained within them, it 

 is not difficult to understand why fish do 

 not react to soundwaves. The volume of 

 sound to which fish are constantly sub- 

 jected is almost unbelievable. Until one 

 has had the opportunity to listen to tJie 

 natural noises in a lake, it is difficult to 

 realize the noise level which can be at- 

 tained. Because the fish are subjected to 

 such noises, it is understandable why the 

 addition of another noise, such as we were 

 introducing, does no more than give them 

 a "start". We do not feel that this reaction 

 is caused by fear as much as an alertness 

 to<a n€W and different noise. This reaction 

 lasts only momentarily, and then the noise 

 becomes just another part of the constantly 

 changing background to which the fish has 

 become adjusted. 



16 



