554 SCHEVILL, BACKUS, AND HERSEY [CHAP. 14 



click, and it is consequently not remarkable that air is usually, but not always, 

 exhausted from the blowhole when the porpoise squeals. (The reader should 

 remember that the larynx is intranarial, and that the mouth is cut off from 

 the respiratory tract.) But the idea that the squeal ("whistle") originates at 

 thp lips of the blowhole is much weakened if one tries whistling under water ; 

 this is our chief reason for not calling the porpoise's squeal a whistle. However, 

 captive odontocetes, notably Tursiops and Globicephala, have been observed 

 with the blowhole out of water and obviously vibrating while somewhat 

 chirping sounds are heard. We tend to discount these performances as not 

 bearing directly on underwater sound, although such competent observers as 

 K. S. Norris of the University of California at Los Angeles disagree with us. In 

 any case, we must consider his and others' suggestions, as yet unpublished, that 

 the larynx may not be the only part of the respiratory tract that may produce 

 sound ; although it has not been proved, some sounds may be produced inside 

 the nasal passages. 



Mysticete sounds are evidently of quite different character (they have 

 usually been described as "moans", and sometimes as "screams"). We know 

 of no direct evidence as to the actual source of these sounds, and so continue 

 to suppose that this is the well-developed larynx. 



7. Spectra of Sounds 



The spectra offish sounds generally have their limits between 50 and 5000 c/s, 

 with most of the sound energy concentrated in the region between 100 and 

 800 c/s. The sounds produced by resonation of the swim-bladder are, in general, 

 lower in tone than those produced by stridulation. Swim-bladder sounds may 

 have components from 50 up to 1500 c/s, but characteristically show principal 

 frequencies in the region of 100 to 300 c/s. Stridulatory sounds, on the other 

 hand, may have components from 50 to 800 c/s or more, but typically are loudest 

 in the region from 500 to 2000 or 3000 c/s. While new data will undoubtedly 

 affect these numbers, it seems reasonably sure that the point made is a valid 

 one. 



The following data give some idea of sound-pressure levels observed near 

 fishes : croaker {Micropogon undulatus) chorus around hydrophone, 63 dynes/ 

 cm2 (overall level in the band from 100 to 10,000 c/s; Knudsen, Alford and 

 Emling, 1948) ; about 20 kinds of fishes, mostly one to two feet from receiver, 

 examined individually, 3.5 to 50 dynes/cm^, highest octave level (Fish, 1954); 

 a toad-fish {Opsanus tau), a few inches from the hydrophone, about 275 dynes/ 

 cm2 in the octave band centered on 200 c/s (Dobrin, 1947). Tavolga estimates 

 that the sounds of the courting male of Bathygobius soporator attain a pressure 

 of 0.1-0.2 dynes/cm2 about 6-8 in. from the hydrophone (Tavolga, 1958), and 

 that those oi Chasmodes bosquianus reach about 0.5 to 0.8 dynes/cm^ (Tavolga, 

 1958a). The latter sounds were just above the noise of his system and could 

 not be detected when the hydrophone was more than a foot from the source. It 

 can readily be seen that fish sounds vary widely in intensity. 



