Tracking interannual variation of a large-scale ocean front influences foraging in a mesopelagic predator

Macroscale ocean fronts aggregate significant biomass and provide critical foraging habitat for large marine predators. These frontal systems shift in response to ocean climate variation, including basin-scale oscillations, and the degree to which marine predators track these movements affect their foraging and reproductive success. Using two decades of adult female northern elephant seal (Mirounga angustirostris) movement data, we assessed their use of the Subarctic Frontal Zone (SAFZ) in the Northeast Pacific Ocean, the SAFZ’s influence on their diving behavior, and its importance to their foraging success. We found that elephant seals followed the interannual movement of the SAFZ and their diel diving behavior became more extreme as they moved closer to the SAFZ, likely reflecting a different vertical distribution of prey in the region. During their short foraging trip, elephant seals that spent time north of the SAFZ, where day and night diving depths were more similar, had greater foraging success. During the long, gestational foraging trip, their geographic distribution relative to the SAFZ did not influence foraging success, but larger animals were more successful, likely due to more efficient diving. Understanding the relationship between dynamic foraging habitat and the response capacity of predator species is critical for assessing the resilience of species and ecosystems as ocean climates become less predictable.