In vivo measurements of lung volumes in ringed seals: insights from biomedical imaging

Marine mammals rely on oxygen stored in blood, muscle, and lungs to support breath-hold diving and foraging at sea. Here, we used biomedical imaging to examine lung oxygen stores and other key respiratory parameters in living ringed seals (Pusa hispida). Three-dimensional models created from CT images were used to quantify total lung capacity (TLC), respiratory dead space, minimum air volume, and total body volume to improve assessments of lung oxygen storage capacity, scaling relationships, and buoyant force estimates. Results suggest that lung oxygen stores determined in vivo are smaller than those derived from typical postmortem measurements. We also demonstrate that—while established allometric relationships hold well for most pinnipeds—these relationships consistently overestimate TLC for the smallest phocid seal. Finally, measures of total body volume reveal differences in calculated body density and net buoyant force that would influence costs associated with diving and foraging in free-ranging seals.