In Vivo Observations of the Bluntnose Sixgill Shark <scp> <i>Hexanchus griseus</i> </scp> (Hexanchiformes: Hexanchidae) in the Western and Central Mediterranean Sea

ABSTRACT The bluntnose sixgill shark ( Hexanchus griseus ), an apex predator, prefers deep waters, making it extremely difficult to obtain reliable estimates of its population due to the challenges posed by such remote environments. This study presents 17 years (2007–2024) of Remotely Operated Vehicle (ROV) expeditions in the Western and Central Mediterranean Sea, opportunistically documenting H. griseus at depths of 50–500 m, near the islands of Capraia, Sardinia, Sicily and in the Bari canyon. Nine sharks were observed in eight encounters, with lengths ranging from 243 to 288 cm. The sharks displayed cautious, curious behaviour approaching the ROV and fleeing when they got too close. The study suggests that ROV emissions influenced the sharks' behaviour. Despite the opportunistic data collected, the small number of encounters could suggest a low‐density population for this species in the region. Our findings provide important in vivo data that will aid in estimating the abundance of H. griseus in its preferred environment and increase our knowledge of this charismatic species.