THE PRODUCTION OF SOUNDS 



219 



Figure 114. Odysseus tied to the mast of his ship to resist the enticing song of the sirens {here 



represented as birds). Note the dolphins in the background. From a Greek painting in the 



Athens Archaeological Museum. {Griinthal, 1952.) 



casual reports of sounds apparently emitted by fishes, and fishermen fi-om 

 the YelloAv Sea had reported that they had been woken up by them. All 

 this, however, was not very reliable evidence. The question had never 

 been investigated properly, partly because of lack of apparatus, and partly 

 because of lack of money. But now that the hydrophone had made its 

 appearance, and that the U.S. Navy provided all the resources, zoologists 

 ^vere quite willing to go into the matter. They soon found that the sea was 

 a veritable babel of sounds resembling falling stones, ships' hooters, 

 rattling chains, saws, moans and squeaks. One of the biggest sources of 

 noise was soon identified as the croaker, a strange fish capable of a sound 

 as loud as 107 decibels. (Cf. the pneumatic drill's 80 decibels, an aircraft 

 engine's iio decibels and a thunderbolt's 120 decibels.) Different fish 

 produce their own characteristic noises, as visitors listening to the special 

 loudspeakers installed in some aquaria have been able to hear for them- 

 selves. Crustaceans, too, are not silent, and the 'snapping shrimp' found in 

 the Pacific is the loudest of all. 



The pitch of the sounds made by all fish so far investigated is rather 

 low - 100-1,500 cycles per second, the noise being most intense at about 

 350 cycles, i.e. in the region of our upper a. (The 'snapping shrimp' emits 

 much higher notes of between 1,000 and 2,500 cycles per second.) Fishes 

 usually produce sounds with their mouths or swim bladders, though their 

 fins may contribute to the general effect. Detailed investigations are still 

 continuing, not only for defence purposes, but also to help the fishing 



