DOUBLE MIGRATIONS OF THE NORTHERN ELEPHANT SEAL, MIROUNGA-ANGUSTIROSTRIS

Adult northern elephant seals go to sea twice each year for periods of less than or equal to 8 months during which they range widely in the northern Pacific Ocean. Using new tracking technology, we showed that the species (and individuals) returned to the same foraging areas duri ng postbreeding and postmolt movements, documenting the first double m igration for any animal. We also showed segregation by sex during both migrations, the causes of which are unknown. Seals dove continually t o depths of 250-550 m during both migrations and travelled Linear dist ances of at least 18,000 (females)-21,000 km (males) during the 250 (m ales)-300 (females) days they were at sea. These are the longest annua l migrations yet recorded for individual mammals. The double migration s apparently are modulated by the requirement for seals to return to l and twice each year, to molt and to breed, although the reasons seals favor distant molting sites on the California Channel Islands over isl and and continental beaches nearer foraging areas are unknown.