Spatial-temporal strategy and fishing practices drive catch composition in FAD-associated tuna purse seine fisheries in the Western and Central Pacific Ocean

The widespread use of drifting fish aggregation devices (FADs) in tuna purse seine fisheries since the mid-1990s has raised sustainability concerns due to increased fishing mortality of unwanted species, such as small-sized tunas and silky sharks ( Carcharhinus falciformis , FAL). A better understanding of ways to mitigate the catch unwanted species while increasing the catch of target species is critical for developing ecosystem-based management approaches. Here, we analyzed fisheries logbook data and scientific observer records of 345 FAD-associated fishing sets collected in the Western and Central Pacific Ocean to assess the influence of spatial-temporal strategies and fishing practices on the catch composition. Results demonstrate that technical adjustments can enhance the potential sustainability of tuna purse seine fisheries. Especially, small-sized tuna catches were concentrated in northern and eastern regions (2°N–6°N, 170°E–175°E), while FAL bycatch exhibited a more widespread distribution. Fishing practices factors, such as the duration of the purse seine gear set (~9 min) and the time of the set relative to sunrise (~30 min); substantially increased tuna catches while minimizing small-sized tuna catches. Seasonal analysis revealed that the pre-closure period (January to June) positively impacted tuna catches and reduced small-sized tuna catches. Moreover, FADs submerged structure at depths of 80 m stabilized tunas and FAL, while small-sized tunas tended to associate with deeper structures (90 m). • This study developed three models to evaluate the influence of spatial-temporal strategies and fishing practices drive catch composition. • Seasonal effects highlighted the positive influence on tuna catches and reduced small-sized tuna catches during January to June. • FADs submerged structure at depths of 80 m stabilized tunas and FAL, while small-sized tunas tended to associate with deeper structures (90 m)