Evidence of site fidelity and deep diving behaviour of scalloped hammerhead shark (Sphyrna lewini) around the Saint Peter and Saint Paul Archipelago, in the equatorial Mid-Atlantic ridge

Abstract

Seven scalloped hammerhead sharks (Sphyrna lewini) were satellite tagged around the Saint Peter and Saint Paul Archipelago (SPSPA), located at the equatorial Mid-Atlantic ridge, to investigate their vertical and horizontal movements. All sharks remained in the surroundings of the SPSPA over the course of the 120-day monitoring period, suggesting a high degree of medium-term site fidelity. During this period, scalloped hammerhead sharks covered a wide extension of the water column, ranging from the mixed layer to the mesopelagic zone. All sharks remained in warm (>22°C) shallow layers most of the time, but also dove to depths greater than 150m, mostly at night, eventually reaching 728m (5.6°C) on two occasions. This study contributes important, novel information on the habitat use and movement patterns of scalloped hammerhead shark in Atlantic equatorial oceanic waters. It also highlights the potential of protecting key, large oceanic areas as a useful tool for the conservation of this endangered species.