A synoptic comparison of the foraging behaviour of Weddell and crabeater seals

The Expert Group on Birds and Marine Mammals (EG-BAMM) has initiated the "Retrospective Analysis of Antarctic Tracking Data" (RAATD) program. This project aims to create a predator community-wide assessment of habitat use in the entire the Southern Ocean. Identifying the basic habitat requirements of Antarctic predators is fundamental to understanding how they will respond to the human-induced challenges of commercial fisheries and climate change. This understanding can only be achieved if the underlying linkages to physical processes are related to animal movements. As part of this effort we are collating and synthesizing the available data on the foraging and movement patterns of Weddell and crabeater seals. While Weddell seals are one of the best studied top predators of the Southern Ocean, significantly less is known about crabeater seals, which are one of the most numerous mammals on the planet. We have synthesized the available tracks on these two seal species for comparison. We compare tracks from a 113 Weddell seals from the Weddell sea, the Antarctic Peninsula, East Antarctica and the Ross Sea and 53 crabeater seals from the Antarctic Peninsula and the Weddell Sea. The foraging behaviour of Weddell seals is surprising similar across the different regions, with dive durations ranging from 8.6 to 12.6 minutes with average ranging between 43 to 69 meters. Weddell seals tended to remain on the continental shelf and had similar movement patterns covering 7 to 13 km/day. In contrast crabeater seals moved greater absolute distances and greater distances per day ranging between 19.2 and 33.6 km/day. Further, their use of the continental shelf habitat varied with 85% of the crabeater seals on the wAP remaining on the shelf while only 24% remained on the shelf in the Weddell Sea