been developed to homogenize nnilk, mix oils, 

 and precipitate snnoke particles. The high 

 frequency sirens have also been used to kill 

 bacteria, fish, frogs, and other small organ- 

 isms. They are effective only at extremely 

 short range (50-60 mm.) with almost no 

 "spread" and require trennendous operating 

 power. These machines are for aerial use 

 only, the orgsinisms being held in containers 

 directly in the sound blast. As yet no under- 

 water "death ray" has been produced because 

 of the difficulty of transducing energy into the 

 water. 



To the average fishery biologist, the diffi- 

 culties of experimenting with sound waves 

 seem alnnost insurmountable. Efficient, con- 

 tinuous, sound wave production lies almost 

 entirely within the realm of electronic war- 

 fare. The equipment used to produce controlled 

 sound is for the most part comprised of 

 complex power amplifiers and underwater 

 speakers containing electromagnetic, magneto- 

 striction, or crystal oscillators. This is not 

 a conti adiction of the definition of sound 

 given earlier. In devices of this type, the 

 amplifier develops the power to operate a 

 signal generator which in turn sends elec- 

 tronic impulses to the mechanical oscillator, 

 or diaphragm. The vibrating diaphragm im- 

 parts sound waves by alternately compressing 

 and rarefying the water. Electronic hydro- 

 phones measure the sound field by reversing 

 this system. 



There are, however, simple mechanical 

 means of making underwater sounds. One of 

 the most productive is the turbine driven 

 with water and air. There are many types of 

 underwater bells, clappers, organ pipes, 

 whistles, and sirens. It is possible to release 

 air and steam to cause noise in the water, 

 and finally, there are explosives. Fishery 

 investigators have experinnented with nearly 

 all of these types to obtain response in several 

 kinds of fishes. Most of the investigators were 

 unaware of the need for knowing how much 

 sound energy they were creating in the water. 

 Moorhouse (1932) used a tapper, a buzzer, 

 a bell, and a motor horn inside a rectangular 

 can at one end of an aquarium. He found that 

 the nervous system of the perch is quite 

 capable of building up a conditioned reflex 

 to sound and that some species of fish were 

 affected more than others. 



The point to be made is that experimentation 

 with sound need not necessarily involve com- 

 plex equipment. Experiments such as those of 

 Moorhouse could be duplicated by anyone. A 

 simple device such as a pneumatic drill 

 operating in a submerged tank might 'prove 

 effective as a fish "scare." It would then be 

 the province of the electronics experts to 

 measure the sound and repi^oduce it in a 



controlled manner for the purpose of guiding 

 snnall fish. 



Although it has been mentioned in the litera- 

 ture that fish tend to be attracted to low 

 frequency sound waves, such statennents ap- 

 parently are not based on more than single 

 observations. The majority of the research 

 work in relation to sound and fish has been 

 concerned with the ability of fish to be con- 

 ditioned to respond to a sound stimulus. Such 

 experiments have shown that most fish con- 

 dition readily and serve as evidence that fish 

 are capable of sound perception. There is, 

 however, little if any indication that fish are 

 consistently attracted or repelled by sound 

 waves of any frequency or amplitude. 



The evidence that the four pieces of pro- 

 fessional sound equipnnent described in this 

 report failed to produce a marked forcing or 

 guiding response in young salmonoids does 

 not detract from the desirability of presenting 

 the methods and results of the experiments, 

 nor should investigators consider that the 

 frequencies tested have been exhaustively 

 covered by these tests. Sound wave qualities 

 and the kinds of transducers used to force 

 this energy into the water are so diverse 

 that the present work must be considered as 

 only exploratory. 



EQUIPMENT AND METHODS 



Rainbow trout from 4 to 9 inches in length 

 (fig. 1) and l/2-inch brown trout were used 

 in most of the tests. The fish were all normal 

 healthy hatchery trout, taken for the most part, 

 from natural raceways. 



The physical equipment set up to measure 

 the reaction of fish to sound by actual count 

 is shown in figures 2, 3, 4, and 5. This con- 

 sisted simply of a 1/2-inch mesh wire trough, 

 100 feet long and 3 feet wide by 3 feet deep 

 with just enough wood framing for support of 

 the wire, plank gangway, and the nine gates 

 separating the trough into 10 sections 10 feet 

 long each. No unnecessary wood was used 

 under water because of possible reflection 

 of sound waves from structural members. 

 The bottom seams of the wire trough were 

 joined by hog rings at 2-inch intervals (fig. 2), 

 so that the entire trough was literally sus- 

 pended from the 1x4 longitudinal members, 

 with the wire bottom a foot above the mud 

 bottom of the pond. The nine gates separating 

 the trough into 10 sections were so rigged 

 that all could be raised or dropped simul- 

 taneously at the beginning and end of each 

 trial. Figure 5 shows the gates down. In 

 figure 4 they are all raised and held in posi- 

 tion as during a sound or control run. The 

 pond in which this structure was built is 450 

 feet long and 60 feet wide. The bottom and 



