Linking courtship calls and observed behaviours of Epinephelus marginatus in the wild offers new insights into its reproduction and conservation

1. Groupers are marine fishes particularly vulnerable to overexploitation owing to their reproduction-related traits. The dusky grouper Epinephelus marginatus is classified as 'Endangered' in the Mediterranean Sea, where protection measures have proven critical for allowing population recovery and persistence of the species. However, knowledge gaps remain regarding its reproductive behaviours and spawning sites. As with other grouper species, the dusky grouper is known to produce courtship-associated sounds, which were validated in captivity, but no study has ever established a link between sound production and observed behaviours in the wild. 2. This study aims to characterize, both visually and acoustically, the behavioural patterns of wild dusky grouper, thus specifically linking visual courtship behaviours to the associated sound production. Visual as well as passive acoustic methods were employed at two presumptive spawning sites within a Mediterranean Marine Protected Area (MPA) in the north-western Mediterranean Sea over two consecutive summer seasons (2017 and 2018). 3. The temporal patterns of sound production showed site specificity over the month in which reproductive activity was most intense. Courtship calls were mostly recorded around sunset at both study sites and were significantly associated with visual reproductive behaviours. Results also indicated a temporal partitioning in the acoustic activity of the species, with different sound types being recorded at distinct times of the day, likely corresponding to the occurrence of various behaviours during those periods. 4. These findings have important implications for identifying and monitoring dusky grouper spawning sites using passive acoustic methods, therefore providing valuable information for the development, implementation, and/or enforcement of effective conservation measures therein.