Gas exchange dynamics in bottlenose dolphins around 2 min apneas conform to values for terrestrial mammals

Cetaceans are often assumed to employ very high oxygen extractions of ∼40-60% and high tidal volumes (60-80% of vital capacity) to decrease surface time and increase foraging time at depth. However, such oxygen extractions and tidal volumes are greatly at odds with gas exchange in terrestrial mammals, and may, if incorrect, lead to severe overestimations of field metabolic rates in wild animals when modelling oxygen uptake from respiration rates. Here we test the hypothesis that bottlenose dolphins have such high average oxygen extractions and tidal volumes. By measuring oxygen extractions and tidal volumes of 2000 breaths before and after a two-minute apnea bout in three trained bottlenose dolphins we show that average pre-apnea resting oxygen extractions are between 17-25%, less than half of what has historically been reported for cetaceans. Following apnea, initial oxygen extractions are high (∼60%) but drop below pre-apnea levels in 11-20 breaths. Tidal volumes in this experimental setting were between 21-37% of vital capacity consistent with recent findings for marine mammals, but less than half the 60-80% often assumed for cetaceans in field metabolic rate modelling. We therefore reject the hypothesis that bottlenose dolphins on average employ high oxygen extractions and high tidal volumes at rest and following short apneas. Consequently, using fixed high values for tidal volumes and oxygen extractions when modelling FMR from breathing rates in wild cetaceans may possibly lead to overestimations of their energy expenditure, food requirements and ecological roles.