Seasonal movements and foraging areas of postbreeding (n = 9) and postmoulting (n = 3) adult southern elephant seal females from Marion Island were studied using Geolocation Time-depth Recorders. Movements were classified into three phases – an outbound transit phase, distant foraging phase, and an inbound transit phase. The longest residence time of postbreeding females during their foraging migrations was in areas at the outer edge of their feeding range (± 1460 km) both to the north and south of the island, largely within inter-frontal zones south of the Antarctic Polar Front (APF) and between the Sub-Tropical Convergence (STC) and the Sub-Antarctic Front (SAF). Postmoulting females travelled further afield (2122–3133 km distant) to the APF, to inter-frontal zones south of the APF (within the pack ice outer edge), as well as to the Antarctic Continental Shelf. This study provides additional information on the putative function of dive types in relation to the movement phases of elephant seal females from Marion Island. The relative frequency of assumed ‘foraging’, ‘exploratory’ and ‘transit’ dive types, as well as the duration and location of the different phases of movement suggest two seasonal foraging strategies. Sea floor topography could possibly cue the transit phases of both postbreeding and postmoulting females from Marion Island.

Adult female survival as a potential proximate factor responsible for observed changes in southern elephant seal Mirounga leonina populations was investigated. We compared the survival rate estimates from mark–recapture data for female elephant seals from the Marion Island population (using program MARK) for two periods (pre- and post-decline) during the past 15 years and with estimates from another population in southern Argentina, which had increased steadily during the same period. Survival of prime-age adult females increased significantly by 6.2% during the latter part of the decline at Marion Island, and the survival of adult females at the colony in southern Argentina was 3.2% greater than at Marion Island after the stabilization. We thereby demonstrated the importance of adult female survival in population regulation and emphasized the importance of monitoring adult females in order to understand population changes in southern elephant seals. In addition, we investigated whether reproductive expenditure early on in life reduces future reproductive potential in the population at Marion Island. We did this by estimating and comparing future survival and breeding probabilities of females primiparous at different ages. The future annual survival and breeding probabilities of females breeding at a young age, was similar to those from females primiparous at an older age. There was also no reduced survival in the year following first breeding in young or older first time breeders. Reproductive expenditure in young primiparous females therefore did not entail future fitness costs relative to older primiparous females, and we found no evidence supporting the existence of various life-history strategies in terms of age of primiparity within a population of southern elephant seals.