SYMPOSIUM ON UNDERWATER SOUND AND ITS 



BIOLOGICAL AND OCEANOGRAPHICAL 



APPLICATIONS 



SOUND AS A TOOL IN MARINE ECOLOGY, FROM DATA ON 

 BIOLOGICAL SOUNDS AND THE DEEP SCATTERING LAYER(i) 



By Martin W, Johnson, Scripps Institution of Oceanography, 

 University of California 



[A bsirad] 



Underwater sounds produced by animals or reflected by them can 

 be used in studying concentrations and behaviour of certain marine 

 populations. 



Biological Sotmds. — Crustacea and fishes are the main sound producers, 

 though whales and porpoises are also capable of making sounds. 

 Crustacean sounds consist mainly of high frequency crackle produced by 

 snapping shrimp. The sound produced by a large population of these 

 shrimp is continuous, and with directional sound equipment their habitats 

 can be detected to distances of 2,000 yards or more. 



Studies of the continuity and sound spectrum level of shrimp gives 

 evidence pertaining to stability of populations, their diurnal activities, 

 geographical distribution, and type of bottom and depth of water 

 preferred. 



Observations on fish noises have given- less useful ecological data. 

 They do, however, demonstrate a regular and pronounced seasonal and 

 diurnal habit of certain Sciaenidse to form localized choruses, as 

 contrasted with isolated solos by the toadfish [Opsanus tau) while 

 guarding its nest or territory. 



Reflected Sounds. — The " deep scattering layer " (a sound scattering 

 layer at 150 to 400 fathoms within the sea) was shown by its diurnal 

 vertical migrations to be biological in nature. The partial reflection of 

 fathometer signals in this layer promises to be a useful ecological tool in 

 studying the distribution, concentration, and movements of the 

 organisms involved in causing the scatter. 



While using sound as a guide, a preliminary study in 1945 showed a 

 positive correlation with plankton stratification, especially the larger 

 plankters, and the depth of the scattering layer. This relationship may 

 be partly secondary, since the more effective scatterers may be larger 

 forms that subsist upon and migrate more or or less concurrently with 

 the plankton. 



Summary of Discussion 



Dr. Tweedie inquired whether the mechanism of Cetacean noise 

 production was known, and it was replied that little work had been done. 

 Seals were known to produce an underwater noise sounding similar to 

 that produced by aerial means, though doubtless produced in a different 

 manner. As regards underwater vocal noises, it was observed that a 

 yell is not discernible, but that a sustained humming vibration is able to 

 be picked up. 



(M 1948, Journal of Marine Research, Vol. 7, No. 3, pp. 443-458. 



207 



