Assessing red hind ( Epinephelus guttatus ) spawning aggregation changes from long-term relative variations in call types associated with reproductive behaviors

Abstract Fish spawning aggregations (FSAs) are elevated concentrations of conspecific fish, often predictable in time and space, that gather for the main purpose of reproduction. For some grouper species, distinct courtship sounds are associated with specific reproductive behaviors, and this association has yet to be elucidated. If known, long-term trends in courtship sounds can thus be used as indicators of change in spawning aggregations. Red hind (Epinephelus guttatus) form spawning aggregations annually at recurring locations and times. Red hind have the ability to produce four distinct types of sounds (labeled RH1–4) that are most commonly heard during FSAs. Of these courtship-associated sounds (CAS), mostly two, produced by males, are used during courtship displays toward gravid females (RH1) and territorial/harem defense with other males (RH2), respectively. To elucidate the role of these two CAS in the red hind reproductive behaviors we analyzed the evolution of the partitioning between RH1 and RH2 call types in acoustic recordings spanning 12 years of spawning seasons, between 2011 and 2022 at a Caribbean FSA, off western Puerto-Rico. The relative temporal variations of call types were linked to the dynamics of the spawning population and suggests that daily to hourly variations in call numbers are linked to changes in sex ratios associated with egress and ingress from and to the spawning site, respectively. Specifically, RH2 was the most common call type during FSA. However, RH1 call type numbers peaked at the time of presumed spawning, while RH2 call type numbers decreased, confirming RH1 association with courtship display toward a female or a harem. At the interannual scale, the evolution of the relative variation of the two call types suggests either a significant change in the sex ratio tending toward a male dominated population or a spatial shift of the spawning site away from the location of the acoustic recorder. Understanding the relative role of call types and monitoring the relative variations of call type numbers in the reproductive dynamics of socially structured populations enables the understanding of potential changes in a spawning aggregation over time that could result from fishing pressure or environmental changes.