The fish were allowed to "settle down", and 

 the 10 -second test was run. The transducer 

 was then raised, the pen was rolled back into 

 the well in the raft, and the number of fish in 

 the various compartments was recorded. Test- 

 ing from the raft was more time-consuming 

 than laboratory testing. 



RESULTS OF LABORATORY TESTING 



The laboratory phase of the research 

 covered the range of sound from 10 through 

 8, 000 c . p . s . (table 1) . Testing included the 

 use of continuous sound, various pulsed sound, 

 and other qualities and quantities of sound, such 

 as the siren type. More than 13, 000 young 

 silver salmon, 3 to 5 inches long, were tested 

 in The experimental tank in the laboratory. Some 

 of the exploratory testing was conducted upon 

 young Chinook salmon 2 to 3 inches long, but 

 these were not used for any of the systematic 

 testing. 



Although some frequencies looked more 

 promising than others, none of the frequencies 

 demonstrated either an attracting or a repelling 

 force great enough to be considered for further 

 investigation. A sample page of test results is 

 found in figure 9 . 



Early in our exploratory testing, it was 

 clearly established that young silver salmon 

 were capable of perceiving sound. Upon the 

 introduction of sound, the test fish always ex- 

 hibited a typical "start", or quick -swimming 

 movement. This act was almost instantaneous, 

 and the distance covered, being only an inch or 

 two, was negligible. After the initial "start", 

 there was no other noticeable reaction by the 

 fish, and it was assumed that they had become 

 conditioned or adjusted to the presence of the 

 sound. This result was common for all the 

 laboratory testing. Even the various types of 

 sounds, such as the siren, pulsed or continuous, 

 made no apparent difference in the reaction of 

 the fish. The initial "start" was the only 

 noticeable response. 



As water is a much better medium 

 for transmitting sound than is air, it is 

 difficult to understand why sounds of the 

 intensities recorded in our investigation 

 did not cause the fish to react. Intensities 

 were measured with a hydrophone con- 

 nected to a vacuum-tube voltmeter. In- 

 tensity measurements were made at the 

 horizontal and vertical center of each com- 

 partment. Sound intensity in the water was 

 measured in millivolts and converted to 

 dynes per square centimeter. There was 

 considerable variation in intenn^ity among 

 the different frequencies, even though all 

 frequencies were being transmitted at the 

 same power input. TTie highest intensity 

 recorded was at a frequency of 1,810 c.p.s.; 

 in the experimental tank, this frequency 

 produced amplitudes as high as 7, 200 dynes 

 per cm2 in compartment No. 1; falling off 

 gradually to a level of 2, 800 dynes per cm2 

 in compartment No . 5. In contrast, some 

 frequencies were so low that a measure of 

 their amplitude was impossible with our 

 equipment . Some intensity levels at various 

 frequencies are shown in table 2 , 



Even though some frequencies were 

 so intense that comparable noise in the air 

 would be almost unbearable to the human 

 ear, there was no apparent reaction by the 

 fish. 



During a study of the sound patterns 

 within the experimental tank at different 

 frequencies, it was determined that particu- 

 larly in the low frequencies there was no 

 gradual fall -off or decay of sound away from 

 the transducer. As was expected, sound 

 intensities in the different compartments 

 varied with the frequencies. It was con- 

 cluded that in some cases the sound was 

 nondirectional, owing to reverberation and 

 standing waves . Sound patterns of this 

 nature were of little use in testing their 

 effect as either an attracting or a repelling 

 force . 



14 



