Novel insights into habitat use, diving and diet of the elusive Ross seal

• Main Authors: Wege, Mia, Bornemann, Horst, Blix, Arnoldus Schytte, Nordøy, Erling S., Bester, Marthán N.
• Format: Conference Object
• Language: unknown
• Published: 2020
• Subjects: Antarc*; Antarctic; Ross Seal; Sea ice; Weddell Sea
• Online Access: https://epic.awi.de/id/eprint/52853/; https://hdl.handle.net/10013/epic.508eb6a3-8a3b-45f6-a486-df4e3b4481d9

Ross seals (Ommatophoca rossii) are the least studied and scarcest of the Antarctic pinnipeds. Only two studies exist on its at-sea movements: four and eight individuals tracked in the Amundsen and Weddell seas respectively. Diving behaviour has only been recorded for seven individuals and no longitudinal stable isotope data exist. Between 2016 and 2019, we deployed 15 satellite trackers of which seven measured diving behaviour and collected whiskers for bulk-stable isotope analyses from 25 individuals, making this the single largest study on Ross seals to date. Tracking data was combined with the eight animals previously tracked in the Weddell Sea to build the first habitat model for the species. Ross seals travelled away from the Antarctic pack-ice to forage pelagically on myctophid fish and cephalopods. This is reflected in the sequentially sampled bulk stable-isotope data from collected whiskers, with oscillations in δ13C and δ15N values reflecting their south-north movements. During winter, they spend most of their time tracking the marginal sea ice while summer is spent in open water. Ross seals dive deeper, but not longer, during the day presumably following the diel vertical migrations of their preferred prey and haul-out behaviour is influenced by lunar phases. The habitat model shows that sea-surface temperature is the most important indicator of foraging behaviour and they prefer to forage in a very narrow temperature band. This contrasts with suggestions that Ross seals might benefit from climate change due to the receding ice and reduced travel distances required to reach the open water.