A study recently published in the journal Ocean and Coastal Management reveals new details about the ecology of two species of deep-sea sharks in the Azores: the kitefin shark (Dalatias licha) and the bluntnose sixgill shark (Hexanchus griseus). The research is the result of a collaboration between the Okeanos biotelemetry team and Miguel Gandra, a PhD student at the Centre of Marine Sciences of the Algarve.
These two species, difficult to study and of increasing conservation concern (one of them classified as endangered), are large predators inhabiting deep waters ranging from 100 to over 1500 metres in depth. Until now, little was known about their behaviour and habitat use in the seas surrounding the Azores.
For over a decade, 21 kitefin sharks were monitored using acoustic transmitters and depth sensors, while sixgill sharks were tagged using acoustic and satellite technology. In an innovative approach designed to minimise the impact on the sharks, some of these tags were deployed directly from an OceanX manned submersible.
The results reveal a frequent and prolonged presence of both species in the region, with periodic detections over more than four years. The sixgill sharks showed broader movement patterns and larger home ranges, whereas the kitefin sharks exhibited more sedentary behaviour, closely associated with island slopes. Both species undertake daily vertical migrations, ascending to shallower waters at night. For kitefin sharks, a clear sexual segregation was also observed, with males and females favouring different depth ranges.
This study emphasises that deep-sea sharks are not all the same, as they exhibit different spatial behaviours. Even in areas far from human sight, these species are under increasing pressure from fishing and the degradation of deep-sea habitats.
Referenced article: https://doi.org/10.1016/j.ocecoaman.2025.107782
Image credits: Nuno Sá | Atlantic Ridge Production
