Insights from venous oxygen profiles: oxygen utilization and management in diving California sea lions

Abstract

SUMMARYThe management and depletion of O 2 stores underlie the aerobic dive capacities of marine mammals. The California sea lion (Zalophus californianus) presumably optimizes O 2 store management during all dives, but approaches its physiological limits during deep dives to greater than 300m depth. Blood O 2 comprises the largest component of total body O 2 stores in adult sea lions. Therefore, we investigated venous blood O 2 depletion during dives of California sea lions during maternal foraging trips to sea by: (1) recording venous partial pressure of O 2 (P O2 ) profiles during dives, (2) characterizing the O 2 -hemoglobin (Hb) dissociation curve of sea lion Hb and (3) converting the P O2 profiles into percent Hb saturation (S O2 ) profiles using the dissociation curve. The O 2 -Hb dissociation curve was typical of other pinnipeds (P 50 =28±2mmHg at pH7.4). In 43% of dives, initial venous S O2 values were greater than 78% (estimated resting venous S O2 ), indicative of arterialization of venous blood. Blood O 2 was far from depleted during routine shallow dives, with minimum venous S O2 values routinely greater than 50%. However, in deep dives greater than 4min in duration, venous S O2 reached minimum values below 5% prior to the end of the dive, but then increased during the last 30-60s of ascent. These deep dive profiles were consistent with transient venous blood O 2 depletion followed by partial restoration of venous O 2 through pulmonary gas exchange and peripheral blood flow during ascent. These differences in venous O 2 profiles between shallow and deep dives of sea lions reflect distinct strategies of O 2 store management and suggest that underlying cardiovascular responses will also differ. Supplementary material available online at

Flipper stroke rate and venous oxygen levels in free-ranging California sea lions

“…To protect and secure the electrode, the insertion site was covered with a small patch of neoprene that was affixed to the animal's fur with fast-setting glue (Loctite 401, Henkel). These procedures and calibrations have been explained in more detail in previous publications (McDonald and Ponganis, 2013;Meir et al, 2009;Ponganis et al, 1991, Ponganis et al, 1997Stockard et al, 2007). Depth and P O2 were recorded at 1 Hz, and three axes of acceleration were recorded at 16 Hz.…”

“…Values of S O2 were calculated using the hemoglobin-dissociation curve from McDonald and Ponganis (2013). Because the minimum calculated aerobic dive limit for this species is 3.4 min (Weise and Costa, 2007) and increased P CO2 contributes to a decrease in pH as dive duration increases (Kooyman et al, 1980), P O2 values collected prior to 3 min into the dive were converted to S O2 using the equation for a pH of 7.4 (log[S O2 /(100-S O2 )]=2.473×log(P O2 )-3.632) and all P O2 values collected beyond 3 min into the dive were converted to S O2 using the equation for a pH of 7.3 (log[S O2 /(100-S O2 )] =2.363×log(P O2 )-3.576).…”

“…Because the minimum calculated aerobic dive limit for this species is 3.4 min (Weise and Costa, 2007) and increased P CO2 contributes to a decrease in pH as dive duration increases (Kooyman et al, 1980), P O2 values collected prior to 3 min into the dive were converted to S O2 using the equation for a pH of 7.4 (log[S O2 /(100-S O2 )]=2.473×log(P O2 )-3.632) and all P O2 values collected beyond 3 min into the dive were converted to S O2 using the equation for a pH of 7.3 (log[S O2 /(100-S O2 )] =2.363×log(P O2 )-3.576). Previous data suggest that California sea lions, and other deep-diving pinnipeds, typically keep core body temperature relatively constant at 37°C while diving (McDonald and Ponganis, 2013;Meir and Ponganis, 2010); therefore, P O2 electrodes were only calibrated at this temperature and temperature effects on the S O2 values were not considered. The time on the TDR/ accelerometer instrument and P O2 logger were synchronized to the same internet-synced computer clock.…”

“…These animals are known for being active swimmers and can dive as deep as 540 m and as long as 10 min, during which they demonstrate a wide range of heart rate responses and blood oxygen depletion patterns (Kuhn and Costa, 2014;McDonald and Ponganis, 2012, 2013. For this study, we equipped free-ranging adult female California sea lions with biologging devices that simultaneously recorded depth, tri-axial acceleration and venous partial pressure of oxygen (P O2 ).…”

Key Questions in Marine Megafauna Movement Ecology

“…For example, we are now able to track and record the physiological state of animals as they travel across entire ocean basins or continents, fly over the highest mountains or dive from the surface to the ocean depths [3][4][5][6]. These types of studies have addressed holistic questions encompassing cross-taxa comparisons in both terrestrial and marine systems that have investigated how animals optimize their locomotion [7]; their search patterns for prey [8] and the factors that constrain their migration distances [9], dive performance [10] and swimming speed [11] ( Figure 2).…”