![]() Hence, three different diel behaviours were identified during the tracking period: (i) regular normal DVM (nDVM) (dawn descent – dusk ascent, with over 90% of nighttime spent above 250 m, and between 5 and 50% of the day below this threshold) (ii) surface-oriented behaviour (occupation of surface waters both day and night), and (iii) deep depth-oriented nDVM. Although blue sharks recurrently use surface waters, cyclic diel behaviours were observed, with >95% of night-time spent above 250 m depth and variable day-time depth use. In this study, we satellite tagged adult blue sharks ( Prionace glauca) in the North Atlantic Ocean to examine behavioural changes in response to the encountered environment, and therefore, to determine potential risks of capture using pelagic longline fisheries data. The drivers of DVM in large predators such as pelagic sharks have only recently begun to be investigated in detail with the advent of sophisticated archival tags and high-resolution oceanographic datasets. In the pelagic environment diel vertical movements (DVM) are widespread across taxa, from zooplankton ascending from day-time depths into surface layers at night to avoid visual predators, to apex predators following prey movements to maximise foraging opportunities. 6Centre for Biological Sciences, University of Southampton, Southampton, United Kingdom. ![]() 5Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton, Southampton, United Kingdom.4Marine Biological Association of the United Kingdom, Plymouth, United Kingdom.3Instituto de Investigaciones Marinas, Consejo Superior de Investigaciones Científicas (IIM-CSIC), Vigo, Spain.2Laboratório Marítimo da Guia, Marine and Environmental Sciences Centre (MARE), Faculdade de Ciências, Universidade de Lisboa, Cascais, Portugal.1Centro de Investigação em Biodiversidade e Recursos Genéticos/Rede de Investigação em Biodiversidade e Biologia Evolutiva (CIBIO/InBIO), Universidade do Porto, Vairão, Portugal. ![]() Marisa Vedor 1,2, Gonzalo Mucientes 1,3, Sofia Hernández-Chan 1, Rui Rosa 2, Nick Humphries 4, David W.
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