Abstract:
Climate variability and changes in sea ice dynamics have caused several iceobligate or krill-dependent populations of marine predators to decline, eliciting concern about
their demographic persistence and the indirect ecological consequences that predator
depletions may have on marine ecosystems. Pack-ice seals are dominant ice-obligate
predators in the Antarctic marine ecosystem, but there is considerable uncertainty about their
abundance and population trends. We modelled the density and distribution of pack-ice seals
as a function of environmental covariates in the southern Weddell Sea, Antarctica. Our
density surface modelling approach used data from aerial surveys of pack-ice seals collected
in the 2013/14 austral summer. Crabeater seals Lobodon carcinophaga, the most numerous
pack-ice seal we observed, occurred at the highest densities in areas with extensive sea ice
near the continental shelf break, but were almost absent in areas of similar sea ice
concentration in the southern extent of the Weddell Sea. The highest densities of Weddell
seals Leptonychotes weddelli, which were less abundant than crabeater seals within the pack
ice habitat, were predicted to occur over the continental shelf, near the shelf break. The distribution of both seal species broadly corresponded with the distribution and relative
abundance of their main prey (Antarctic krill Euphausia superba and Antarctic silverfish
Pleuragramma antarctica) obtained from concurrent ecosystem surveys. Ross seals
Ommatophoca rossii and leopard seals Hydrurga leptonyx were not detected at all and are
apparently rare within the southern Weddell Sea. These results can contribute to biodiversity
assessments in the context of marine protected area planning in this region of the Southern
Ocean.
