Large-scale passive acoustic monitoring of fish sound production on the West Florida Shelf

Abstract

Sounds from toadfish Opsanus sp., and 4 other suspected fish sounds were identified in passive acoustic recordings from fixed recorders and autonomous underwater vehicles in the eastern Gulf of Mexico between 2008 and 2011. Data were collected in depths ranging from 4 to 984 m covering approximately 39000 km 2 . The goals of this research were to map the spatial and temporal occurrence of these sounds. Sound production was correlated to environmental para - meters (water depth, lunar cycle, and dawn and dusk) to understand the variability in seasonal calling. Toadfish 'boatwhistles' were recorded throughout the diel period, with peaks observed between 15:00 and 04:00 h. Annual peaks coincided with the spawning period in the late spring to early summer. The 4 unknown sounds were termed: '100 Hz Pulsing', '6 kHz Sound', '300 Hz FM Harmonic', and '365 Hz Harmonic'. The 100 Hz Pulsing had the temporal characteristics of a cusk-eel call with frequencies below 500 Hz. Sound production was observed mainly at night with annual peaks in the spring and fall. The 6 kHz Sound was observed exclusively at night between 15 and 50 m bottom depths; occurrence decreased significantly in the winter. The 6 kHz Sound peak frequencies correlated positively to satellite-derived sea surface temperature (SST) and nega tively to chlorophyll concentration. The 300 Hz FM Harmonic was observed largely (89%) at night and appeared offshore (40�200 m depth). The 365 Hz Harmonic was observed 98% of the time at night, inshore (<40 m depth). The fundamental frequency of the 365 Hz Harmonic was positively correlated with SST, reflecting a temperature-driven increase in sonic muscle contrac- tion rate; conversely, call duration was negatively correlated. The ubiquity of these 4 unknown sounds illustrates how little is known about biological communication in the marine environment.