natural habitat. Understandably, perhaps the experimental aspects of our 

 project were overshadowed by the more productive techniques of passive observa- 

 tion. 



Diving techniques involved use of both open circuit SCUBA and the closed circuit 

 G.E. Mark X rebreather. The ability to leave the habitat at will any time of 

 the day or night provided the freedom necessary for effective observation of 

 the behavior of our subjects in relation to sound production. Bubbles produced 

 by open circuit diving gear hampered our attempts to observe organisms while 

 using it. Not only did the bubbles create a great deal of noise but they 

 frightened the subjects to the point of appreciably altering their behavior. 

 We, therefore, customarily used open circuit apparatus while performing work 

 tasks not directly associated with behavioral observation. Nevertheless, we 

 did obtain a significant amount of data while using the SCUBA units. 



The rebreather units were invaluable to us during the observational periods 

 indicated above. Their low noise level and lack of bubbles allowed us to 

 approach the subjects very closely without interfering with the organisms nor- 

 mal behavior pattern or with the recordings we were making. At times while 

 wearing the rebreather and remaining quite still, we were treated as a portion 

 of the substrate. With the rebreather on we found that after a short while we 

 were able to detect with the unaided ear both the background noises and the 

 sounds produced by fishes and certain invertebrates. This was developed into a 

 method by which we were able to trace the source of at least one interesting 

 sound commonly only heard at night, the frog chorus. 



Some of the most interesting observations were made at station 1 while looking 

 out of the wet room window from the habitat. The view from these hemispherical 

 windows is superior to that experienced by a diver in the water because of its 

 panoramic nature. One can detect a great deal more of what is actually happen- 

 ing in the environs of the subjects being observed while looking through these 

 domes. At the same time, while inside the habitat, it was a simple matter to 

 don earphones and listen directly to the organisms while taking notes on their 

 behavior. Unfortunately, the habitat produced such a high-level of noise and 

 the closest part of the reef was so far away from the window, ten meters, that 

 the full potential of such dry observation could not be realized. 



The sound spectrum analyzer is presently being employed on a continuing basis 

 to provide us with visual representations of the recorded sounds which enable 

 us to describe them in terms of frequency, amplitude and temporal structure. 



DESCRIPTION OF SOUNDS 



The volume of data collected during Mission 4-50 was such that its thorough 

 assessment is taking longer than anticipated. We are currently in the process 

 of enumerating and quantifying the sounds recorded in an effort to abstract a 

 picture of the diel variations in the nature and intensity of sound production 

 by several species of squirrelf ishes and by grazers and coral feeders in general. 

 A final phase in analysis of our data will involve assessment of sound produc- 

 tion in relation to behavioral observations made by divers. 



At the present time, it is possible to present spectral analyses and descriptive 

 discussions of certain sounds which have been abstracted from our tapes for 



VI-85 



