Biodiversity in the bycatch community of Chinese tuna longline fisheries in the Pacific Ocean

Abstract The biodiversity of the bycatch community in tuna longline fisheries has historically been under-studied. In this study, observer data from 9744 sets of Chinese tuna longline fisheries were used to estimate the biodiversity of the bycatch by applying alpha diversity measures, and their habitat preference was predicted with the Generalized Additive Model. A total of 98 bycatch species were observed, mainly consisting of bony fishes and elasmobranchs. We found that there was a similar species composition in the ALB (Thunnus alalunga) and BET (Thunnus obesus) sets that was different in abundance assemblages. Regarding the entire study area, biodiversity in the tropical Pacific was higher than that in the temperate Pacific, and it was highest in the eastern tropical Pacific. In the western Pacific, higher pelagic biodiversity was noted between 15° and 20° latitude. The species richness and diversity were largely influenced by geographical positions, sea surface temperature and fishing depth. The indicators of species richness and density performed well in identifying the hotspots of biodiversity. This study helps to understand the predator biodiversity in pelagic ecosystems and identify, for conservation purposes, critical habitats for the bycatch community in tuna longline fisheries.