Metabolic costs of submerged activity in three species of Arctic seals

Arctic seals live in dynamic environments characterized by the seasonal advancement and retreat of sea ice. These amphibious marine mammals rely on sea ice as a haul-out substrate for rest and key life-history events, but they spend the majority of their time in the water. Current and predicted sea ice loss highlights the importance of estimating the costs of in-water activities when modelling the energy budgets of free-ranging seals under changing conditions. Yet, activity-specific costs are not available for many affected species. We used open-flow respirometry to measure and compare resting metabolic rates with the energetic costs of submerged diving and swimming in spotted (Phoca largha; n = 3), ringed (Pusa hispida; n = 1) and bearded seals (Erignathus barbatus; n = 1). Individuals were trained to voluntarily complete a sustained stationary breath hold under water or a continuous submerged swim before surfacing in a metabolic dome to measure rate of oxygen consumption. Metabolic rates decreased 11-24% relative to resting metabolic rate for the spotted and ringed seals while diving for 3, 5, or 7 min and did not change with increasing duration. The bearded seal did not show a similar decrease in diving metabolism. All individuals exhibited notable energetic increases to support exercise underwater while swimming at preferred speeds for 2-3 min. Metabolic costs were 243% and 114% above resting levels for spotted and ringed seals, but only 60% greater for the bearded seal. These results reveal the conflicting physiological responses of metabolic suppression while submerged (i.e. dive response) with the oxygen requirements of active swimming (i.e. exercise response) in Arctic seals and highlight the unique physiology of the bearded seal. The cost of submerged activities can now be considered in quantitative models of ice seal energy budgets, improving understanding of how physiological differences influence species-specific tolerance or vulnerability to rapidly changing Arctic conditions.