Abstract:
In the Southern Ocean, wide-ranging
predators offer the opportunity to quantify how animals
respond to differences in the environment because their behavior and population trends are an integrated
signal of prevailing conditions within multiple marine habitats. Southern elephant seals in particular, can
provide useful insights due to their circumpolar distribution, their long and distant migrations and their
performance of extended bouts of deep diving. Furthermore, across their range, elephant seal populations
have very different population trends. In this study, we present a data set from the International Polar Year
project; Marine Mammals Exploring the Oceans Pole to Pole for southern elephant seals, in which a large
number of instruments (N = 287) deployed on animals, encompassing a broad circum-Antarctic
geographic
extent, collected in situ ocean data and at-sea
foraging metrics that explicitly link foraging behavior
and habitat structure in time and space. Broadly speaking, the seals foraged in two habitats, the relatively
shallow waters of the Antarctic continental shelf and the Kerguelen Plateau and deep open water regions.
Animals of both sexes were more likely to exhibit area-restricted
search (ARS) behavior rather than transit
in shelf habitats. While Antarctic shelf waters can be regarded as prime habitat for both sexes, female seals
tend to move northwards with the advance of sea ice in the late autumn or early winter. The water masses
used by the seals also influenced their behavioral mode, with female ARS behavior being most likely in
modified Circumpolar Deepwater or northerly Modified Shelf Water, both of which tend to be associated
with the outer reaches of the Antarctic Continental Shelf. The combined effects of (1) the differing habitat
quality, (2) differing responses to encroaching ice as the winter progresses among colonies, (3) differing
distances between breeding and haul-out
sites and high quality habitats, and (4) differing long-term
regional
trends in sea ice extent can explain the differing population trends observed among elephant seal
colonies.
