DEVELOPMENTAL ASPECTS OF SLEEP-APNEA IN NORTHERN ELEPHANT SEALS, MIROUNGA-ANGUSTIROSTRIS

Northern elephant seals, Mirounga angustirostris, breathe irregularly while sleeping on land, alternating bouts of breath-holding (apnoea) that can last up to 25 min with periods of breathing (eupnoea). Our aims were to quantify changes in this behaviour during development and to determine the correspondence between these ontogenetic changes and those independently recorded in the dive durations of free-ranging seals. We observed 163 seals during periods of apparent sleep, ranging in age from new-born to adult, at Ano Nuevo, California. Mean length of apnoea and percentage time spent in apnoea were 3.1 min and 59% in neonates (0-4 days old). These values decreased to 1.8 min and 37% in suckling pups (5-28 days old), then increased with age thereafter, reaching about 8.0 min and 60% in adults of both sexes. Sleep apnoea duration and percentage time spent in sleep apnoea increased most markedly after weaning, when the animals were learning to swim and dive. Mean sleep apnoea duration and mean dive duration increased in a similar way during the first year of life; thereafter, mean sleep apnoea duration reached an asymptote while mean dive duration continued to increase. We conclude that the elephant seal's ability to sustain long apnoeas is not only an adaptation for foraging underwater but also a means for conserving water and energy while fasting on land.