Vertical movements at a daily cycle, exhibited by a range of zooplankton and nektons, are primarily caused by diel changes in light intensity and associated shifts in predation risk and prey availability (Hays 2003). Yet, many marine animals do not stay at a particular depth but exhibit vertical return movements or oscillations with various cycles and amplitudes (Hays 2003 Andrzejaczek et al. These gradients, coupled with eco-physiological characteristics of each species and intra- and interspecific interactions such as competition and predation, determine the vertical distributions of marine animals (Longhurst 1967 Giske et al. Marine environments are characterised by vertical gradients of physical (e.g., temperature, light level, oxygen concentration) and biological properties (e.g., primary production). Thus, behavioural thermoregulation linked to foraging, rather than enhanced abilities to control heat exchange rates, is likely key to the expanded thermal niches of this ectothermic species. Furthermore, our comparative analyses showed that the heat exchange rates of blue sharks during the warming and cooling process were not exceptional among fishes for their body size. We conclude that, instead of alternating foraging and rewarming, blue sharks at our study site forage and thermoregulate continuously in the water column. Similar swimming events, detected from the entire tag data (20 − 22 h), occurred over a wide depth range (5 − 293 m). 2.5-h video footage showed a shark catching a squid, during which a burst swimming event was recorded. Sharks shifted between descents and ascents before muscle temperature reached ambient temperature, leading to a narrower range (8 ☌) of muscle temperature than ambient temperature (20 ☌). 422 m), muscle temperature changed more slowly than ambient water temperature. We used electronic tags, including video cameras, to record the diving behaviour, muscle temperature, and foraging events of two blue sharks. Blue sharks are the widest-ranging pelagic shark with expanded vertical niches, providing a model for studying foraging–thermoregulation associations. However, it is unclear how prevalent this pattern is among species. Some species (e.g., bigeye tuna, ocean sunfish) apparently alternate foraging in deep cold waters and rewarming in shallow warm waters. Large pelagic fishes often dive and surface repeatedly as if they were airbreathers, raising a question about the functions of these movements.
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