Climate-scale hydrographic features related to foraging success in a capital breeder, the northern elephant seal Mirounga angustirostris

Abstract

In marine ecosystems, physical and biological processes act at multiple temporal and spatial scales to influence the distribution of prey species and subsequently habitat selection of for- aging apex predators. Understanding how apex predators may respond to climate changes requires knowledge of habitat selection in relation to measures of foraging success at spatio-temporal scales relevant to the question and analytical approach. In this study, we used satellite telemetry from 75 adult female northern elephant seals Mirounga angustirostris, coupled with point measures of for- aging success (energy gain), to examine habitat selection at large temporal and spatial scales. The main hydrographic ecoregion used on the post-moult (PM) migration was the Transition Zone, while on the post-breeding (PB) migration, females focused on the Subarctic Gyre. Characteristics of area- restricted search (ARS) behaviours, as determined by the fractal landscape method (such as time spent in ARS, total distance travelled in ARS and number of ARS) also differed significantly between the PM and PB migrations. Underlying differences in prey composition and/or distribution may drive the differences seen in searching behaviour and foraging success of elephant seals at large scales. Despite these differences, seals showed comparable levels of foraging success across both migrations and in all ecoregions. Foraging success was notably greater than measured in previous studies. These results highlight the benefits of a capital breeding strategy to a relatively slow-moving, large verte- brate predator allowing individuals to exploit large areas of the heterogeneous North Pacific.