Evening fish choruses near coral reef systems in the Great Barrier Reef, Australia

Abstract

The nighttime ambient sea noise on and around coral reef systems in northern Australia is characterized by choruses produced by nocturnally active fishes. These choruses are produced year round, from dusk to dawn. Choruses are composed of many ‘‘pops’’ of between 5 and 28 ms length, with a decay envelope suggestive of a lightly damped swimbladder and with source levels calculated at 154–157 dB re: l μPa2 at 1 m peak to peak. Sources are found mostly concentrated over 6–20 m water depth. Choruses have a mean spectral peak at 550 Hz (normal range 500–750 Hz) but may influence sea noise from 100 Hz to 3 kHz. The highest chorus levels occur just after dusk or in the early evening, reaching up to 35 dB above background levels. The recorded levels of choruses displayed distinct daily patterns, lunar patterns with higher levels around new moon periods, and seasonal patterns of highest level during the austral summer. Choruses occur over large spatial scales, with active sources heard at up to 15 km from reef systems and chorus influence on ambient sea noise extending considerably further. It is believed that nocturnal planktivorous fishes, such as those from the families Holocentridae and Priacanthidae, are responsible for choruses. [Work supported by the Australian Defence Science and Technology Organization.]