Long-term individual niche fidelity in southern elephant seals

Fidelity to foraging sites is potentially beneficial to individual animals utilising habitats characterised by patchily distributed resources, as in a number of marine mammal species. We assessed inter-annual and long term (up to eight year) patterns in spatial distribution and depth use for southern elephant seals (Mirounga leonina) instrumented with satellite-relay data loggers over multiple foraging migrations from Marion Island, southern Indian Ocean. Individual seals displayed very high levels of fidelity to spatial areas used during their at-sea migrations, with inter-annual home ranges overlapping on average by 72% (max. >90%). Patterns of spatial distribution remained similar for individuals tracked over longer time periods, where home ranges consistently overlapped by more than 50% between migrations, even after periods of up to seven years. Patterns of depth use were generally also consistent between migrations, with individuals mostly targeting similar depth layers between successive migrations. Furthermore, in situ water temperatures at the median dive depths of seals overlapped substantially between migrations, with overlap ranges between 49% and 70%. Our study is the first to show that elephant seals display high levels of foraging niche fidelity, as assessed by spatial areas used, vertical depth layers targeted, as well as in situ thermal conditions. While elephant seals are known to display substantial behavioural plasticity within migrations, inter-migration stability in habitat use patterns may confer long-term energetic advantages to individual seals. Such behavioural consistently likely also plays important roles in advancing patterns of resource partitioning and avoidance of intra-specific competition