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) t hat can last up to 25 min with periods of breathing (eupnoea). Our aim s were to quantify changes in this behaviour during development and to determine the correspondence between these ontogenetic changes and th ose independently recorded in the dive durations of free-ranging seals . We observed 163 seals during periods of apparent sleep, ranging in a ge from new-born to adult, at Ano Nuevo, California. Mean length of ap noea and percentage time spent in apnoea were 3.1 min and 59% in neona tes (0-4 days old). These values decreased to 1.8 min and 37% in suckl ing 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 afte r weaning, when the animals were learning to swim and dive. Mean sleep apnoea duration and mean dive duration increased in a similar way dur ing the first year of life; thereafter, mean sleep apnoea duration rea ched an asymptote while mean dive duration continued to increase. We c onclude that the elephant seal's ability to sustain long apnoeas is no t only an adaptation for foraging underwater but also a means for cons erving water and energy while fasting on land.