In terms of frequency, the staccato pulses cover a wide width. Most of the 

 acoustical energy, however, seems to be focused in two areas of the spectrum. 

 The most intense expenditure of energy occurs between 200 and 400 Hz where the 

 amplitude appears to rise at least 30 decibels (db) above the lowest level of 

 background noise (Figure 4A) . A secondary mode in amplitude occurs at around 

 600 Hz and here the amplitude rises to 30 db above background only in the first 

 pulse. The rest of the pulses shown an amplitude 6 db lower at this frequency. 



Coos can barely be detected in sonogram 3B but are plainly visible in 4A . Their 

 similarity to staccatos is readily apparent. The one conspicuous modal ampli- 

 tude occurs between 200 and 400 Hz just as in the staccato. Obviously, the 

 higher frequency components have been extinguished but this is consistent with 

 the nature of sound transmission in water where lower frequency sounds persist 

 over greater distances than do those of high frequency. All this seems to 

 indicate that the sounds referred to as coos are actually distant staccatos 

 given a different tonal quality by a reduction in overall intensity and a 

 greater relative amplitude loss at the higher frequencies than at the lower. 



Pops: 



These sounds (Figure 4B were produced by the Reef Squirrelfish, Adioryx 

 coruscus . The individual responsible for them was sole inhabitant of a small 

 crypt in the reef. Commonly, however, these fishes were found under coral 

 heads in the company of numerous cardinal fishes and a few small Longspine 

 Squirrelf ishes, Flammeo marianus . Both the Reef Squirrelfish and the Longspine 

 are sound producers and encounters between the two species led to some inter- 

 esting acoustical exchanges. This relationship is one which we hope to look 

 into further in the near future. Popping sounds have been elicited from a 

 captive Reef Squirrelfish in our lab, but these are quite different in nature 

 from those detected in the natural habitat due in part to the acoustical prop- 

 erties of the small tank. 



Basically, the pops recorded on the reef consisted of one pulse each and are 

 spaced very irregularly. It seems likely that each pop pulse is individually 

 initiated and one is not specifically linked to another in the way pulses of 

 the previously discussed staccato sounds are. 



Most interesting is the frequency structure of each pulse. The presence of two 

 predominant frequencies in a pulse of this sort is not especially unique; how- 

 ever, the two frequencies, in this case approximately 850 Hz and 5 to 40 Hz, 

 are separated by a rather broad band of about 800 Hz. The lowermost frequency 

 is somewhat lower than any major component of the other sounds analyzed during 

 this study. This observation may be of particular significance in separating 

 these pops from similar sounds produced occasionally by the Longspine Squirrel- 

 fish. 



The amplitudes at both predominant frequencies rose approximately 36 db above 

 the quietest background. 



Pops elicited from the reef squirrelfish in a 10-gallon tank show a much broader 

 apparent range of frequencies than do the pops recorded in the environment. 

 This could be due in part to the conditions under which the sounds were emitted. 

 In the laboratory, a great deal of agitation of the fish, which was considerably 



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