Mediterranean fish vocalize in deeper environments than previously thought

A study conducted by the Laboratory of Functional and Evolutionary Morphology (FOCUS Research Unit/Faculty of Sciences), the CHORUS Research Institute, in collaboration with STARESO and Alseamar, has shown that Mediterranean fish emit sounds at higher depths than previously thought. Until now, in the Mediterranean Sea, fish acoustic communication was reported up to a maximum of 40 m depth; this new knowledge has strong potential implications for the monitoring and management of deep-sea fish populations. This study was published in the Journal of Acoustical Society of America.

T

he oceans are filled with several sound sources, including many fish species which emit sounds under a variety of conditions such as when breeding, competing for mating resources or defending territories. Fish have evolved the largest diversity of sound-producing mechanisms among vertebrates, resulting in a wide variety of sounds being emitted, with characteristics which are specific to each species. Just as birds can be identified by their songs, fish can be identified by the sounds they produce. By listening to fish sounds, researchers can achieve information about which species is present in a specific environment and where and when it prefers to aggregate.

Few studies have reported the probable presence of fish sounds in deep waters, but none of these was carried out in the Mediterranean Sea. Here, fish sounds have been reported at a maximum depth of 40 meters.

A team of researchers from the Laboratory of Functional and Evolutionary Morphology of ULiège and the Research Institute CHORUS (France), in collaboration with STARESO (France) and Alseamar (France), wanted to find out whether fish sounds can be heard at greater depths than those previously monitored. In addition to this, the researchers aimed to investigate the potential of different passive acoustic monitoring configurations for providing information on fish populations, which could have implications for the monitoring of fish stocks. In order to do this, the team used a combination of Static Acoustic Monitoring (SAM: acoustic recorders deployed on the seafloor) and of Mobile Acoustic Monitoring (MAM: hydrophones integrated into new-generation automated underwater vehicles, called "gliders") to monitor vocal fish communities in a Mediterranean underwater canyon. These methods are completely non-invasive and make possible to assess the temporal and spatial distribution patterns of calling individuals.

During the summer of 2016 and 2017, three SAM and one MAM campaigns were conducted in the Calvi submarine canyon. In total, 194 hours of recordings were analysed for the diversity of sounds emitted by fish and for their abundances.

Biological sounds were detected in 38% of the recorded audio files," explains Marta Bolgan, a post-doctoral researcher at the Laboratory of Functional and Evolutionary Morphology and first author of the article. "In addition to the presence of clicks and whistles from marine mammals, 10 types of sounds (for a total of more than 9,000 sounds) with characteristics similar to those emitted by vocal fish species were characterized; for one of them, the identity of the emitter could be inferred at the genus level (Ophidion species). The greatest acoustic richness was detected at the head of the canyon (about 100m deep), while one type of sound was recorded when the glider was in the mid-water (about 200m deep) above a depth of more than 1000m," says the researcher.

This study, recently published in the Journal of Acoustic Society of America, demonstrates for the first time that fish vocalize also in deeper Mediterranean environments than those traditionally monitored, and that the combination of static and mobile acoustic monitoring can provide important information on the diversity and dynamics of deep-sea fish populations.

This study paves the way for a new field of research, which uses the monitoring of sounds emitted by deep-sea fish to deduce important information about deep-sea fish populations," concludes Eric Parmentier, director of the ULiège Laboratory.

Scientific reference

Marta Bolgan, Cédric Gervaise , Lucia Di Iorio Julie Lossent, Pierre Lejeune, Xavier Raick, Eric Parmentier,  Fish biophony in a Mediterranean submarine canyon, The Journal of the Acoustical Society of America 147, 2466 (2020)