High dive efficiency in shallow water

Abstract Dive studies across mammals, birds, reptiles and fish often focus on deep dives, shallow water diving has tended to be overlooked. For air-breathers, foraging in poses challenges since the lungs generate buoyancy, divers must trade off extent of inhalation against negative buoyancy needed avoid floating surface. Using high-resolution depth loggers, we addressed this knowledge gap around ecology at a site for hawksbill turtles ( Eretmochelys imbricata ) where was typically < 3 m. Contrary predictions, dive durations were long, particularly night (mean duration per turtle: 17–61 min, n = 12 turtles, 2576 nocturnal dives), despite warm temperatures (24–37 °C). efficiency (% time submerged) hawksbills 98%, highest recorded any air-breathing marine vertebrate including penguins (60–78%), seals (51–91%), cetaceans (68–87%), other sea turtle species (68–95%). Hawksbills usually much longer (42–286% increase) than green loggerhead when temperature are accounted for. Hawksbill likely forage very reduce predation risk from sharks: 423 captured by hand, none had evidence shark attack, although large sharks present nearby deeper water. Our results challenge prediction that dives air-breathers will short open way comparative range taxa. work emphasises importance shaping patterns habitat utilisation.