Oxygen Storage Capacity

Blood is the most important storage site of oxygen in phocid seals, as it contains approximately 65% of the total oxygen stores, followed by the muscle (30%) and the lungs (5%) (Kooyman 1985, 1989). Blood oxygen storage capacity is determined by hemoglobin concentration and blood volume (Snyder 1983). Diving animals tend to have higher hemoglobin concentrations and blood volumes than terrestrial animals. Among marine mammals, the deeper and longer duration divers have the highest hemoglobin concentrations and blood volumes (Ridgway and Johnston 1966; Sleet, Sumich, and Weber 1981; Duffield, Ridgway, and Cornell 1983; Snyder 1983; Kooyman 1985, 1989), and as we would expect from adult diving performance, these values have been reported to be high for northern elephant seal pups (Simpson, Gilmartin, and Ridgway 1970; Castellini, Costa, and Huntley 1986; Hedrick, Duffield, and Cornell 1986; Wickham 1989). Changes in these values with development have received little attention. A. M. Kodama, R. Elsner, and N. Pace (1977) reported that mass specific blood and hemoglobin concentrations increased during the first year in the harbor seal, Phoca vitulina . M. M. Bryden and G. H. K. Lim (1972) reported that southern elephant seals, M. leonina , increased their mass specific blood volume during the postweaning fast and during the first trip to sea, an increment that is similar to what we observed in northern elephant seal pups (table 15.1). By the time juvenile elephant seals are ready to go to sea for the first time, their body is 14.4% blood, as compared to 21.2% blood for an adult female (P. Thorson, unpubl. data).

Total oxygen stores increase rapidly to a high level in developing elephant seals, due to increases in blood and muscle oxygen stores (table 15.1). When it is time to make the first trip to sea, these young juveniles have already amassed mass specific oxygen stores of 60.3 ml/kg, 73.5% of the mass specific oxygen stores recorded in adult females (82.1 ml/kg) (P. Thorson, unpubl. data). The oxygen stores in juvenile elephant seals are similar to those found in adult phocids of other species (Kooyman 1985, 1989).