Respiratory pattern of the Southern elephant seal (Mirounga leonina) resting on land: an analysis of ontogenetic development.

Understanding the respiratory patterns of marine mammals on land can provide insight into their respiration and breath-hold diving physiology at sea. In this study, we analyzed the respiratory patterns of southern elephant seals (Mirounga leonina) resting on land, emphasizing ontogenetic variations. We observed 478 elephant seals at Península Valdés, Argentina, and recorded 16,626 respiratory cycles through direct observation and video analysis to evaluate differences in breathing phases: inspiration (INSP), post-inspiratory pause (PIP), expiration (EXP), and post-expiratory apnea (PEA). All seals displayed episodic breathing patterns, with the PIP phase significantly longer (4.3 ± 6.67 s) compared to INSP and EXP (1.5 ± 1.30 s and 1.2 ± 1.1 s, respectively). We found respiratory cycles were longer and frequencies lower in older seals, corresponding to allometric scaling with body size and physiological maturity. PEAs were infrequent, representing only 1.6% of cycles, but their occurrence and durations increased with age, possibly consistent with greater oxygen storage capacity. Additionally, we found ground temperature influenced respiratory phases, particularly shortening the EXP and INSP duration at higher temperatures, indicating a potential thermoregulatory adaptation. State of wakefulness also influenced PEA occurrence, with a higher probability of occurrence during a presumably asleep state. Our findings contribute to understanding the physiological adaptations enabling the aquatic lifestyle of elephant seals and underscore substantial developmental changes in respiratory control during terrestrial resting periods.