Rhyming in the cold: first evidence of soniferous fishes in the Southern Ocean

Abstract Acoustic ecology of Southern Ocean fishes is currently unknown due to lack of dedicated fish acoustic research from those remote/inaccessible areas. The objective of this study was to investigate the monthly and diel acoustic occurrence pattern of benthic fishes relative to environmental conditions at the sub‐Antarctic Prince Edward Islands (PEIs) in the Southern Ocean. To collect our passive acoustic data, we used an autonomous recorder deployed at ~167 m water depth on an oceanographic mooring over 21 months (April 2021 to December 2022). Benthic Ski‐Monkey III towed camera was deployed around the PEIs to identify potential sources of recorded underwater fish sounds. Three types of sounds (pops, grunts and drum sounds) were detected and validated using random forest models based on their characteristics. Pops and grunts were produced in series and as singlets. Pops were the most frequently detected sounds and were detected in December 2021 through May 2022, whereas grunts were detected in January through March 2022. Drum sounds were rare and were detected as singlets on a few occasions in December 2021 through March 2022. These monthly fish occurrences correspond to the breeding season of fishes in the Southern Ocean, suggesting the use of acoustic cues during breeding. From camera footage, Nototheniops larseni (painted notothen) was the only fish species found around the acoustic recorder location, and pops were putatively attributed to this abundant species, whereas other sounds were attributed to other observed species. Fish sound occurrence increased around sunrise and sunset. Sea surface temperatures between 5.2°C and 8°C were the primary predictor of fish acoustic occurrence, underscoring the potential vulnerability of these fish to environmental change. This study provides the first evidence of monthly and diel acoustic occurrence of soniferous fishes and demonstrates that bioacoustics can monitor fish biodiversity and breeding phenology in the Southern Ocean.