Subsurface swimming and stationary diving are metabolically cheap in adult Pacific walruses (Odobenus rosmarus divergens).

Walruses rely on sea-ice to efficiently forage and rest between diving bouts while maintaining proximity to prime foraging habitat. Recent declines in summer sea ice have resulted in walruses hauling out on land where they have to travel farther to access productive benthic habitat while potentially increasing energetic costs. Despite the need to better understand the impact of sea ice loss on energy expenditure, knowledge about metabolic demands of specific behaviours in walruses is scarce.

Lung function assessment in the Pacific walrus () while resting on land and submerged in water.

In the present study, we examined lung function in healthy resting adult (born in 2003) Pacific walruses () by measuring respiratory flow ([Formula: see text]) using a custom-made pneumotachometer. Three female walruses (670-1025 kg) voluntarily participated in spirometry trials while spontaneously breathing on land (sitting and lying down in sternal recumbency) and floating in water. While sitting, two walruses performed active respiratory efforts, and one animal participated in lung compliance measurements.

Cardiorespiratory coupling in cetaceans; a physiological strategy to improve gas exchange?

In the current study we used transthoracic echocardiography to measure stroke volume (SV), heart rate () and cardiac output (CO) in adult bottlenose dolphins (), a male beluga whale calf [, body mass () range: 151-175 kg] and an adult female false killer whale (, estimated : 500-550 kg) housed in managed care. We also recorded continuous electrocardiogram (ECG) in the beluga whale, bottlenose dolphin, false killer whale, killer whale () and pilot whale () to evaluate cardiorespiratory coupling while breathing spontaneously under voluntary control. The results show that cetaceans have a strong respiratory sinus arrythmia (RSA), during which both and SV vary within the interbreath interval, making average values dependent on the breathing frequency ().

Comparative Respiratory Physiology in Cetaceans.

In the current study, we used breath-by-breath respirometry to evaluate respiratory physiology under voluntary control in a male beluga calf [, body mass range ( ): 151-175 kg], an adult female (estimated = 500-550 kg) and a juvenile male ( = 279 kg) false killer whale () housed in managed care. Our results suggest that the measured breathing frequency ( ) is lower, while tidal volume ( ) is significantly greater as compared with allometric predictions from terrestrial mammals. Including previously published data from adult bottlenose dolphin () beluga, harbor porpoise (), killer whale (), pilot whale (), and gray whale () show that the allometric mass-exponents for and are similar to that for terrestrial mammals ( : 1.