Hearing and acoustic orientation in marine animals 4 | | 



sound. They found the auditory threshold to be approximately constant from W) 

 to 1600 c.p.s. at slightly above 0-01 dyne/cm- or approximately H)-"^ watt cm-. This 

 threshold energy flux corresponds closely to the minimum human threshold m air 

 (between 2000 and 4000 c.p.s.), but the catfish is considerably more sensitive at lower 

 frequencies. Above about 2000 c.p.s., on the other hand, this fish's threshold rises 

 much more steeply than the human threshold. 



AUTRUM and Poggendorf also demonstrated that the catfish's responses depended 

 upon sound pressure rather than amplitude or particle velocity. They confirmed the 

 earlier quaUtative findings of von Frisch et al. that fish without air bladders have 

 thresholds roughly 30 db higher than the catfish. Other experimenters have reported 

 that the Ostariophysii at least can discriminate between sounds dilTering in frequency 

 by as little as 1/4 octave (Wohlfahrt, 1939; Dukgraat and Vereijeb, 1949; and 

 Kleerekoper and Chagnon, 1954). Directional sensitivity, or the ability to localize 

 the source of an underwater sound, has not yet been adequately demonstrated, and 

 indeed both Reinhardt (1935) and von Frisch and Dijkgraaf (1935) obtained 

 negative results in attempts to demonstrate locaUzation of sound sources by stationary 

 fish. On the other hand, Kleerekoper and Chagnon concluded, on the basis of 

 extensive observations and photography of the movements of Semotilus in a tank 

 approximately one metre square, that these small members of the order Ostariophysii 

 could immediately turn towards the louder of two equidistant sources of 50 c.p.s. 

 sound. 



A possible case of echo-sounding in fish 



Having thus reviewed the overwhelming evidence for a high degree of auditory 

 sensitivity in fish, it must be admitted that very little critical evidence is available to 

 indicate what significance sound may have in fish behaviour. Rather than sum- 

 marizing unsatisfactory anecdotal evidence I shall merely describe one observation 

 that suggests the occurrence of echo-sounding by a deep sea fish, with the hope that 

 the need for substantial and imaginative investigation of auditory behaviour in fish 

 will thus be emphasized. I am indebted to Dr. J. B. Hersey of the Woods Hole Oceano- 

 graphic Institution for permission to make a detailed study of a series of underwater 

 sound recordings made north of Puerto Rico in water approxmiately 5100 metres 

 deep. Among many hours of recordings made far from land, that include noises of 

 biological origin, those made about 3 p.m. on March 7. 1949 contain several loud 

 calls, each followed after a short interval by a fainter repetition of itselt. n listening 

 to these sounds, it is difficult to avoid the impression that they are the calls of some 

 marine animal followed by echoes of these calls. While no similar ca Is and apparent 

 echoes have been noted subsequently, as far as 1 can ascertain, a briet analysis ot this 



'''?:^^^^. were a crystal hydrophone, amplifiers, filters, and receding 

 equipment sensitive to 5(^1200 c.p.s. The hydrophone was w.Uun ^^ -^ ;' ^^ 

 surface, and the background noise level was 75-80 db above O'^XX) d n . 1 h 



calls of what was dubbed the " echo fish " consisted of ^^-t notes lasn 1 3 o 

 seconds, and having a rather constant frequency of about 5(^0 _p.s^ J^^^^^ 

 was not precisely cahbrated, but the calls were typically two to thrc t.r^c the b ack 



ground noise level, and occasionally the -^^-''-^''^y^'Z^'^'^J^^^^^^ 

 TTie interval between the loud call and its faint repetition was quite constant, and 



