PASSIVE AND EXPERIMENTAL BIO-ACOUSTICAL 



STUDIES ON MARINE ORGANISMS IN 



THEIR NATURAL HABITAT 



Thomas J. Bright and William W. Schroeder 



Texas A&M University 



College Station, Texas 



ABSTRACT 



A total of 13 sounds, or assemblages of sounds, observed and 

 recorded during TEKTITE II Mission 4-50 are analyzed, described 

 and compared in terms of their frequency, amplitude and temporal 

 structure. Major components of reef associated noise appear 

 most intense at frequencies of approximately 200 to 600, 3500 and 

 5500 Hertz. An amplitude heirarchy of sounds is recognized and 

 briefly discussed, as are certain cyclical and ethological aspects 

 of sound production on reefs. 



OBJECTIVES 



Our primary objective during Mission 4-50 was to gather information concerning 

 the nature, origin and significance of biologically generated sounds in and 

 around the reefs adjacent to the TEKTITE II habitat. Specifically we sought to: 

 (1) obtain a detailed bio-acoustical survey of selected study areas, paying 

 particular attention to diel (24 hour) fluctuations in content and level of 

 ambient biological noise; (2) assess sound production patterns in individual 

 species and determine when and to what extent they contribute to the overall 

 background noise; (3) investigate experimentally and by passive observation 

 and the natural and artificial stimuli which elicit sound production in species 

 involved, both in the field and under laboratory conditions; (4) deteinnine as 

 far as possible the role of sound production in the behavior and biology of 

 acoustical dominants in their natural habitat; and (5) assess the results of 

 these efforts when compared to those of a similar study to be made in the same 

 or an adjacent area but utilizing conventional diving gear and surface based 

 techniques . 



EQUIPMENT 



The acoustical apparatus used consisted of two basic recording units. One was 

 portable, self-contained, and could be carried by a diver. The other made use 

 of a recording unit mounted inside the habitat. Figure lA illustrates the con- 

 figuration of our portable unit. Basically, it consisted of a Sony TC-110 

 cassette recorder housed in a plexiglass case built by us. Input to this 

 recorder was through 25' of shielded cable from an Atlantic Research LC-50 

 hydrophone. This system had an effective frequency response of 40-cycles per 

 second (Hz) to 10-kilocycles per second (KHz) . We had the option of mounting 

 to the recorder a Kodak M-24 Super-8 movie camera in an Ikelite underwater 

 housing. Circuitry was provided which allowed us to operate either camera or 

 recorder independently, or both simultaneously. 



VI-82 



