Continuous, deep diving in female northern elephant seals, Mirounga angustirostris

Abstract

The free-ranging dive pattern of seven adult female northern elephant seals (Mirounga angustirostris) was obtained with time–depth recorders during the first 14 – 27 days at sea following lactation. The instruments were recovered and mass gain at sea determined when the animals returned to the rookery at Año Nuevo, California, to molt. The seals gained a mean of 76.5 ± 13.9 kg during a mean of 72.6 ± 5.0 days at sea. The mean dive rate was 2.7 ± 0.2 dives/h and diving was virtually continuous during the entire period at sea. Mean dive duration was 19.2 ± 4.3 min with the longest submersion lasting 48 min. Mean surface interval between dives was 2.8 ± 0.5 min, so that only 14.4% of the recorded time at sea was spent on the surface. Surface intervals did not vary with the duration of preceding or succeeding dives. Modal dive depth for each female was between 350 and 650 m. The maximum dive depth was estimated at 894 m, a depth record for pinnipeds. The deep, nearly continuous dive pattern of female northern elephant seals differs from the dive pattern of other pinnipeds and appears to serve in foraging, energy conservation, and predator avoidance.