Patterns of fish calling in a nearshore environment in the Great Barrier Reef

Long-term sea-noise statistics have been obtained from a region of the cent ral section of the Great Barrier Reef. Fish calling was a major contributor to sea-noise levels. Calling was either in choruses, where groups of fishe s called en masse, or. as isolated calls repeated ad nauseam. Four calling types predominated, with each displaying unique call characteristics and ca lling patterns through time and space. Analysis of call types offered infor mation on the fish's calling physiology, behaviour and, through thr call's interaction with the local environment, on the location of the caller. Call types ranged from less than 10 ms to several seconds long, and were compri sed from one to nearly 40 pulses. The structure of each pulse was related t o swim-bladder mechanics; normally swim-bladders were lightly damped. Fish calling was most common during the Australian summer with one call type als o displaying lunar trends. All calls had daily patterns of sound production with highest activity levels generally at night. There was some spatial se paration of zones of highest call rates, but sources avoided competition fo r the 'sound space' primarily by offsetting the time of chorus or maximum c all rate. On some occasions, a call type attributed to nocturnal planktivor ous fishes may have ensonified much of the Great Barrier Reef.