FURTHER BIO-ACOUSTIC STUDIES OFF THE WEST COAST OF NORTH BIMINI, BAHAMASl JOHN C. STEINBERG, WILLIAM C. CUMMINGS, BRADLEY D. BRAHY, ANDJUANITA Y. MAcBAIN (SPIRES) Institute of Marine Science, University of Miami ABSTRACT With acoustic-video techniques of observation, eight marine animal sounds were identified and an additional four were tentatively identified. These included sounds from longspine squirrelfish, queen triggerfish, bi- color damselfish, grouper, ocean surgeon, slippery dicks, jacks, cowfish, and drums. The sounds ranged from single pulses having duration times of fractions of a second and train durations of up to several seconds. cycles per second (cps) to trains of pulses having pulse repetition rates of fractions of a second and train durations of up to several seconds. Sound production was associated with feeding, locomotory, and agonistic behavior. The results of playback of these and other sounds were evidence of habituation by two species of snapper, and avoidance reactions. Some information obtained suggests interspecies communication by sound. Choruses of marine animal sounds contributed significantly to the am- bient noise level in the frequency range above 200 cps in the area of study. The studies suggested more effective instrumentation and methods of observation. INTRODUCTION The abundance of underwater biological sounds and the clarity of the water off Bimini, Bahamas, have attracted several workers in the field of marine bio-acoustics (Fish, 1954; Moulton, 1958; Fish & Mowbray, 1959; Kumpf & Loewenstein, 1962; Steinberg et al., 1962; Cummings, 1963, 1964; Cummings et al., 1964; Kumpf, 1964). Biologists, physicists, and engineers at the Institute of Marine Science, University of Miami, have been engaged in a four-year study of underwater sound with the Acoustic- video System located on Bimini. The primary objectives of the most recent phase of the bio-acoustic work were ( I) to determine the source of previously unidentified sounds, (2) to learn more of the behavior associ- ated with sound production in the natural environment, (3) to describe temporal characteristics of the occurrence of recently identified sounds, (4) to observe the reaction of marine animals to the playback of certain sounds into the natural environment, and (5) to evaluate the uses and limitations of the Acoustic-video System in such studies. This paper ,presents results relative to these objectives. MATERIAL AND METHODS The area of study was situated on the bottom, at a depth of 60 feet, IContribution No. 657 from The Institute of Marine Science, University of Miami. This paper constitutes a report of research done with financial support from the U.S. Office of Naval Research contract Nonr 840(13). 1965] Steinberg et a/.: Bia-A caustic Studies Off Bimini 943 about one mile off the west coast of North Bimini, Bahamas. Approxi- mately 50 yards seaward from the study area, the bottom begins to slope abruptly. Several hundred yards further, at a depth of 150 feet, there is a nearly vertical drop-off to 480 feet. The face of the drop-off has protruding shelves of calcarenite capped with sand which apparently had cascaded down the slope, and a heavy growth of alcyonarians (Fig. 1). On the sandy slope above the wall are scattered areas of the sea grasses, Syringadium and Tha/assia, isolated patch reefs consisting of alcyonarians, corals, sparse algal growths, and numerous fishes and invertebrates. A list of fishes from the vicinity of the study area is given in Table 1. Some of these species and FIGURE 1. The drop-off at 250 feet depth, 300 yards west of the study area. This is a calcarenite precipice covered with sand from the above slope and a heavy growth of alcyonarians. Note the long filaments of Cirrhipathes spira/is (Linnaeus). (Photo by William J. Bunton, U.S. Navy Electronics Laboratory.) 944 Bulletin of Marine Science [15(4) a description of the study area were noted by Kumpf (1964). In April, 1963, the underwater television (UTV) camera, four 500 W floodlights, a sound projector, and three hydrophones were moved near a grass bed in the above area. Unless otherwise stated, information presented here was obtained in this general area. Prior to April, 1963, the submerged equipment was located about 150 yards south of the grass bed. The underwater components were cable-connected to the Lerner Marine Lab- oratory where a television receiver was monitored and sounds were recorded. A complete description of the electronic equipment and the methods of recording was given by Kronengold et at. (1964). Sounds on magnetic tapes and other data were analyzed at the Institute of Marine Science with recorders, amplifiers, calculators, and sound analyzers. The period of study extended from January, 1963, to June, 1964; however, earlier information is included and designated as such. During the period of study, 64 magnetic tape recordings each of 24-hour duration were made with hydrophones in the locations described above. Approximately 300 man-hours were used for video observations. Supplementary observations LLJ u 32 z LLJ a:: 28 a:: ~ N : 17,436 u 24 u 0 20 lI- 0 16 t- z 12 LLJ u 8 a:: LLJ CL. 4 J F M A M J J A S 0 N 0 J MONTHS FIGURE 2. Graph showing the monthly occurrence of roar-like sounds from the gastropods Strombus sp. and Cassis sp. These are pooled data over a three- year period, representing 17,436 individual occurrences. 1965] Steinberg et aZ.: Bia-A caustic Studies Off Bimini 945 were made to a depth of 250 feet using SCUBA in the vicinity of the submerged equipment. In addition to a kinescope recorder and a Polaroid camera, which were mounted in front of the UTV receiver, underwater still and movie cameras were used to record observations. Biological specimens were collected using spears, traps, hook and line, and toxicants. The common and scientific names of identified fishes follow those listed by Bailey, et at. (1960). POPS - H. rufus RASP - !:!: bivlttatus 2500 2500 2000 2000 1500 1500 1000 I ! I II 1 1 I 'I' , I I 1000 500 1 " ':.1 I ~~~:...Li.,~<' 500 50 ,ur'~',.,oar I '"," ~ 50 ~ 2~ 10 2.0 CRUNCH B. vetulo BURST· 2500 2000 1500 II 1000 a z o U 5~ 1.'*••'. lLJ (/) 1.0 2.0 RATTLE - B. velula 85 2500 a.. 2000 ~ 1500 d 1000 G 500 Z 50 >- 1.0 2.0 u CHIRP - E Z ~or!itus lLJ 2500 ::;) 2000 0 a:lLJ 1500 l.L.. 1000 500 Ii 50 1.0 2.0 POP - A. bohionus 2500 2000 oo1סס 4000 1500 1000 2000 1 500 150 .. '·'''''·-V"''''''''''~·'·'I''·'''''I'''''..i 50 0.4 0.8 1.2 1.0 20 TIME IN SECONDS FIGURE 3. Sonograms showing the time-frequency characteristics of recently identified and tentatively identified marine animal sounds recorded from the study area at Bimini. 946 Bulletin of Marine Science [15(4) IDENTIFIED MARINE ANIMAL SOUNDS Previous papers concerning bio-acoustic research with the Acoustic- video System, reported the behavior of sound producers and the identifica- tion of some sounds recorded from the area of study. These sounds included a burst sound from margates, Haemulon album, as they picked up benthic organisms from the sandy bottom, pop sounds associated with plankton feeding by margates and other species, blast sounds from the rapid swimming movements of certain species in the area of the hydro- phones, a rasping sound from the radula of feeding conchs, Strombus sp., the scraping sounds of moving hermit crabs, and a roar-like sound from large gastropods, Strombus sp. and Cassis sp., moving across the bottom (Cummings et al., 1964; Kumpf, 1964). A plot of the monthly distribution of roar-like sounds for the last three years shows that conchs in the area of study were more numerous or more active during the summer months (Fig. 2). Although an increase in activity of the conchs could be a contributing factor, SCUBA dives and video observations indicated that there were more conchs in this area during the summer months. Since January, 1963, eight additional marine animal sounds were identified and four others were tentatively identified in the area of study. Most of the identified sounds originated with residential fishes as opposed to transient fishes which occasionally swam through the area. Longspine squirrelfish, Holocentrus rufus.-The vicinity of the study area lacks natural reef habitats and any object placed on the bottom was colonized by reef fishes within a few days. Consequently, every bottom component of the submerged instrumentation was colonized by species which are typical reef dwellers. Among these were longspine squirrelfish. During the daylight hours, one squirrelfish frequented a crevice in the base supporting the sound projector. When ch:lsing intruders away from its territory, the occupant produced a series of resonant pops resembling those from a Geiger counter near a radioactive source. Similar series, produced by motionless squirrelfish confronted by intruders, were followed by the intruder's rapid departure suggesting the possibility of int~rspecies com- munication by wund. These responses were observed on numerous occa- sions during the study by the authors, although it could not be determined if the same individual was involved. The sounds were similar to the rapid volleys of Holocentrus ascensionis, described by Moulton (1958), and the staccato calls of H. rufus, noted by Winn et ai. (1964). Our obser- vations agree with those of Winn and his co-workers in that fin erection and dashing frequently accompanied sound production. Squirrelfish pops were produced individually at irregular intervals or in short series of 3 to 20 pulses. Individual pops were about 0:02 seconds in duration. The length of time between pops averaged 0.1 seconds. Among the squirrelfish sounds analyzed was a series of 19 pops which occurred in 2.0 seconds 1965] Steinberg et at.: Bio-Acoustic Studies Off Bimini 947 (Fig.