SECT. 4] SOUND PRODUCTION BY MARINE ANIMALS 561 



Likewise undemonstrated is any possible role of sound in navigation, either 

 on a local scale (beyond what has been said of Tur stops) or in the long migra- 

 tions that many marine animals are known to make. 



9. Hearing as Related to Sound Production 



In all cases where sounds produced are for intraspecific communication 

 (including, of course, echo-location, which is talking to oneself), they must be 

 heard by the species producing them. In cases of interspecific communication 

 (for defensive and offensive functions) it would not seem essential that the 

 producer of sounds hear them. 



A list of fishes in which hearing has been demonstrated, together with the 

 frequency ranges observed, has recently been compiled by Lowenstein (1957), 

 and it is apparent that the spectral distributions of sounds so far studied 

 principally lie within the limits of fish hearing, which in general lie between 

 50 c/s and 1 to 3 kc/s, except in ostariophysan fishes which may hear up to 

 5 to 13 kc/s. (There have been few, if any, studies of hearing in sound-producing 

 fishes, but doubtless the studies made in other species can be safely extrapolated 

 to include the soniferous sorts.) It is not yet apparent what the correlation is, 

 if any, between the acuity of hearing and the ability to produce sound. It has 

 been suggested that, while many fishes possessing accessory hearing organs are 

 apparently silent (for instance, the clupeids which are mute and have the 

 swim-bladder connected to the ear), others may compensate for relatively poor 

 hearing by the production of loud sounds (as in the toad-fishes, sea-robins and 

 sciaenids). On the other hand, one can find numerous examples among ostario- 

 physan fishes (all of which have accessory hearing organs) in which the ability 

 to produce sound is well developed. 



The bottle -nose porpoise, Tur slops truncatus, hears sounds in the range from 

 150 c/s to about 120 kc/s (Schevill and Lawrence, 1953). Hearing limits have 

 not been determined for other cetaceans. 



Hearing has been little studied in the crustaceans. Jahn and Wulff (1950) 

 say that : ". . . although insects probably comprise the only group in which it is 

 highly developed, it should not be assumed that phonoreception is completely 

 unimportant in the life of other arthropods." Special sound-producing mech- 

 anisms in crustaceans indicate that hearing does play a role in the lives of these 

 animals, unless the sounds prove to be solely defensive in nature (which at 

 present seems not to be so). 



10. Eliciting and Suppressing Marine Animal Sounds 



Some attention has been paid in recent years to the possibility of influencing 

 the movements of fishes by means of man-made sounds. In general fishes quickly 

 accustom themselves to a strange sound after an initial "startle" reaction 

 (Moulton and Backus, 1955). There have been, however, some interesting 

 observations in connection with the effects of foreign sounds on the sound- 

 producing behavior itself in soniferous fishes. Small explosives detonated at the 



19— s. I. 



