On the attraction of larval fishes to reef sounds

Several recent studies have shown that some larval fishes will approach underwater speakers that broadcast reef noise, leading to the hypothesis that larval fishes use acoustic cues to locate reefs for settlement. The purpose of the present study was to examine existing hearing data of fishes in relation to ambient sound levels around reefs to estimate the distance over which reef fish might detect reefs sounds, and to highlight how future data should be collected to answer this important question. The few available measurements of larval fish hearing indicate that they have poor acoustic sensitivity relative to sound levels found around reefs. The apparent poor sensitivity of larval fishes to sound pressure suggests that particle motion, the back and forth motion of water that is associated with acoustic pressure, is the principal stimulus for larval fish hearing. To estimate the maximum distance of orientation to reefs, the acoustic particle velocity of reef sound was calculated from measurements of the acoustic pressure on and away from shore, assuming conditions of a planar propagating wave. Based on these calculations, we propose that larval fishes in acoustically unbounded habitats most probably cannot detect the ambient noise of particle motion at distances >1 km. To better understand the distances over which larval fishes can detect sounds from reefs, more studies on larval fish hearing and reef noise are needed. Larval fish hearing measurements need to independently distinguish sensitivities to particle motion and acoustic pressure. Likewise, independent measurements of particle motion around reefs are required.