Antarctic seals and the sea-ice environment

Given the sensitivity of the sea-ice zone to global warming (IPCC SROCC 2019), there is an urgent need for determining how top predators use their physical and biological environment, in order to understand and predict their response to climate change in the different Antarctic regions. Events such as calving of large icebergs provide a framework for natural experiments to study the consequences of habitat variations on higher trophic level populations. Because the occurrence of such extreme events around Antarctica is predicted to increase due to global warming, it is now timely to study the ecological response of higher trophic levels to calving of large icebergs and their oceanographic consequences. We propose to take advantage of the unique opportunity offered by the recent Mertz Glacier Tongue calving in Adélie Land (Feb. 2010) to continue an unprecedented time-series on the winter foraging movements and in-situ oceanographic conditions of an ice-dependent top predator, the Weddell seal, spanning over 16 years and encompassing this significant climate event. Using vertical T/S/chlorophyll profiles collected by the seals during their dives in winter, we will link their foraging behaviour to in situ hydrographic conditions before and after the Mertz Glacier calving, and assess impact of the Mertz Glacier calving on ocean/sea ice interactions and primary production in the Dumont d’Urville region, and their potential consequences on the seals foraging behaviour. We will provide new insights on how the physical ocean parameters control the primary production under sea ice. We will complete our time-series on the foraging ecology of Weddell seals during summer (post breeding), during which ice retreat stimulates primary production. We also propose to use seal borne micro-sonars to detect the prey field encountered by the seals to study their feeding ecology at a fine scale. We will continue to develop new ways of measuring otherwise poorly sampled key sea-ice parameters such as sea-ice thickness and sea-ice algae biomass using seal-borne sensors. By so doing, we will simultaneously address urgent questions on upper trophic levels ecology, primary production processes in and below sea-ice, and sea-ice/ocean interactions in an innovative and cost-efficient way. We also propose a new study on Weddell seals vocal communication. Pinnipeds use vocalizations in all their social interactions and vital function such as mate selection, territorial defence, mother-young interactions and predator alert. In many pinniped species, mother and pups recognize each other using vocalisations. Up to now, studies on mother-pup vocal recognition on phocids are scarce, and thus further experimental studies are needed. We intend to i) investigate the onset of mother-pup vocal recognition by performing in-air playback experiments on both mothers and pups at different age; ii) investigate underwater vocal communication between mother and pup by using two types of acoustic tags on the mother and/or on the pup; and iii) assess the underwater vocal activity of Weddell seal at Dumont d’Urville year around, by using passive acoustic monitoring.