Modeling spatio-temporal dynamics of Patagonian toothfish spawning in Kerguelen waters using CPUE data

The act of spawning of fish can be influenced by a variety of factors, including environmental conditions and human activities, particularly fishing. Patagonian toothfish ( Dissostichus eleginoides ) is a commercially exploited fish species, occupying the southern Patagonian and Chilean shelves, as well as the sub-Antarctic submarine plateaux. It is characterized by a late maturity and slow body growth, which are key considerations in its management and conservation. In this study, we investigated the spatio-temporal dynamics of Patagonian toothfish spawners in the Kerguelen region using fishery observer data, from 2020 to 2024. We predicted spawner hotspots and seasonal trends of spawner abundance using spatially-explicit Generalized Additive Models (GAMs) that modeled the spawner CPUE (Catch Per Unit of Effort). Our results suggest that toothfish female spawners aggregate at specific locations from early June to the end of July. Hotspots of male spawners were found from mid-June to mid-July and then from mid-August to mid-September. The main spatial overlap between male and female spawner hotspots is located on the western slopes and the north of Skiff bank (along the 1500 m isobath) and in the north-western region (near the 500 m isobath). Our findings enabled the formulation of hypotheses concerning the ecological drivers influencing Patagonian toothfish spawning and emphasize the importance of considering seasonal localized closures to avoid mortality and disturbance during spawning. • Two peaks of spawner abundance were found for Patagonian toothfish. • Spawner peaks occurred in distinct areas: western slopes and north of Skiff Bank. • Male and female spawner hotspots overlapped more in July, in time and space. • Spawners occurred mostly at 1500–1800 m, and locally in shallower waters (500 m). • Seasonal closures in key spawning zones may help manage the fishery.