Dive depth and dive duration data of female southern elephant seals from Marion Island between 2004 and 2008 with links to datasets

The at-sea behaviour of marine top predators provides valuable insights into the distribution of prey species and strategies used by predators to exploit patchily distributed resources. We describe the water column usage and dive strategies of female southern elephant seals from Marion Island tracked between 2004 and 2008. Dives representing increases in forage effort were identified using a method that combines dive type analyses and the calculation of relative amounts of time that animals spend in the bottom phases of dives. Results from this analysis indicate that female elephant seals from Marion Island tend to display lower levels of forage effort closer to the island and display intensive opportunistic forage bouts that occur at a minimum distance of approximately 215 km from the island. Females from Marion Island dived deeper and for longer periods of time, compared to females from other populations. Most animals displayed positive diel vertical migration, evidently foraging pelagically on vertically migrating prey. A few animals displayed periods of reverse (negative) diel vertical migration, however, diving to deeper depths at night, compared to daytime. This behaviour is difficult to explain and prey species targeted during such periods unknown. Our results illustrate plasticity in foraging behaviour of southern elephant seals, as well as inter-population differences in forage strategies.

Ice thickness measurements in the Lincoln Sea and adjacent Arctic Ocean

Results of helicopter-borne electromagnetic measurements of total (ice plus snow) sea-ice thickness performed in May 2004 and 2005 in the Lincoln Sea and adjacent Arctic Ocean up to 86° N are presented. Thickness distributions south of 84° N are dominated by multi-year ice with modal thicknesses of 3.9 m in 2004 and 4.2 m in 2005 (mean thicknesses 4.67 and 5.18 m, respectively). Modal and mean snow thickness on multi-year ice amounted to 0.18 and 0.30 m in 2004, and 0.28 and 0.35 m in 2005. There are also considerable amounts of 0.9-2.2 m thick first-year ice (modal thickness), mostly representing ice formed in the recurring, refrozen Lincoln Polynya. Results are in good agreement with ground-based electromagnetic thickness measurements and with ice types demarcated in satellite synthetic aperture radar imagery. Four drifting buoys deployed in 2004 between 86° N and 84.5° N show a similar pattern of a mean southward drift of the ice pack of 83 ± 18 km between May 2004 and April 2005, towards the coast of Ellesmere Island and Nares Strait. The resulting area decrease of 26% between the buoys and the coast is larger than the observed thickness increase south of 84° N. This points to the importance of shear in a narrow band along the coast, and of ice export through Nares Strait in removing ice from the study region.