Satellite tags describe movement and diving behaviour of blue sharks Prionace glauca in the southwest Pacific

The blue shark Prionace glauca is the most abundant, widely distributed and exploited pelagic shark species. Its population is declining in almost all major oceanic basins. Population management and conservation efforts have traditionally depended on fishery bycatch and observer data. Recent studies correlating animal distribution derived from satellite tags, with commercial fishery impacts, across multi-jurisdictional regions, have provided an improved data platform for population management. Here we present the first fishery-independent data of blue shark distribution in the southwest Pacific Ocean. Fifteen blue sharks were satellite tagged, adding to the global dataset of approximately 179 individuals successfully tracked using bolt-on satellite tags. Smart Position and Temperature (SPOT) tags transmitted between 66 and 505 d, and SPLASH tags between 200 and 343 d. Individual track lengths ranged from 3000 to 14 559 km, spanning 10 exclusive economic zones, from latitudes 0.1 degrees to 43.1 degrees S, and longitudes 160.1 degrees E to 150.8 degrees W. Horizontal movements revealed age/sex segregation and large-scale horizontal migration patterns. Dive data collected with SPLASH tags showed fine-scale vertical habitat use at depths between 0 and 1364 m and temperatures of 5 to >30 degrees C. Behavioural events, such as foraging, searching and travelling, were inferred from commonly repeated patterns in the retrieved dive profiles. This study provides a characterisation of critical habitat use in a region never before sampled, adding to the global understanding of blue sharks, and the fishery-independent database necessary to inform blue shark population management.