Flutter: 



During aggressive displays involving apparent territorial defense and/or 

 chasing, violent movements of the fishes bodies and fins create a disturbance 

 accompanied by fluttering sounds. We successfully recorded many such sounds 

 in the case of the Blackbar Soldierfish, Myripristis jacobus . This fish cus- 

 tomarily hovers above a particular coral head in a more or less constant loca- 

 tion, turning back and forth to keep its head toward the direction of the surge. 

 Occasionally when a fish of the same or another small species approaches too 

 closely, a fluttering chase will ensue and the invader will retreat. Figure 13B 

 illustrates one of these flutters. The region of maximum acoustical energy for 

 the flutter sound is partially obscured by the habitat noise between 100 and 

 500 dbs. Nevertheless, it is apparent that the last two of the five basic 

 pulses comprising the flutter reach 30 db above the quietest background 

 detected. Pulses 1, 2, 4, and 5, therefore, demonstrate an energy maximum at 

 about 300 Hz with recognizable components ranging from below 100 Hz to nearly 

 2000 Hz. Pulse 3, however, demonstrates an energy maximum at about 800 Hz and 

 apparently lacks the pronounced lower frequency structure of the other four 

 pulses. Fluttering sounds such as this can be expected to demonstrate a great 

 deal of variability and it is unlikely we will find any two exactly alike. 



CONCLUSIONS 



The sounds associated with coral reefs in the vicinity of Lameshur Bay, St. John, 

 U.S. Virgin Islands, predominate in a frequency range below 6000 Hz. The most 

 conspicuous sounds, background clicking and crackling and frying pan- like noises, 

 are quite energetic at 3500 and 5500 Hz. The often equally important chorus of 

 larger squirrelf ishes, H. ascensionis , and possibly H. rufus , expend maximum 

 energy at much lower frequencies, 200 to 600 Hz. 



Definite cyclical patterns are evident for certain conspicuous sounds, vis., 

 squirrelf ish chorus and frog-like sounds, whereas the clicking and crackling, 

 attributed at present to the activities of snapping shrimp and physical occur- 

 rences, demonstrate not as yet definable periodicity. Periodicity also seems 

 less pronounced in the case of some of the less evident purposeful sounds. An 

 in-depth consideration of the cyclical aspects of the various sounds described 

 herein must await further analysis. 



Most of the sounds possess distinctive frequency, amplitude and temporal rela- 

 tionships which may serve to distinguish them when analyzed with the aid of a 

 sound spectrum analyzer. Some sounds, particularly staccatos and pops, pulses 

 of which appear very similar and almost indistinguishable to the unaided ear, 

 are obviously separable upon examination of their respective sonograms. On the 

 other hand, sounds easily distinguished by ear (frog-like sound vs. staccato) 

 appear quite similar on sonograms but still separable due to subtle variations 

 in frequency amplitude relationships. 



Most of the sounds are obviously associated with some behavioral occurrence or 

 activity pattern, viz., feeding crunches of Parrotfish, lunging swooshing crunch 

 of the Trumpetfish, flutter of the Blackbar Soldierfish chase, popping, quacking 

 and squeaking door sounds of the Longspine Squirrelf ish-Reef Squirrelfish rela- 

 tionship, grunts of alarmed Groupers, etc. Many of these situations are yet to 

 be investigated in detail. It is felt that, when well understood, the behavior 



VI-104 



