Habitat use and diet of the Ross seal in the eastern Weddell Sea

Horst.Bornemann [ at ] awi.de


The Ross seal (Ommatophoca rossii) is the least studied of the Antarctic pack-ice pinnipeds. Currently only two publications on the at-sea movements (n = 14 individuals) and three publications on their diving behaviour (n = 16 individuals) exist. Furthermore, only one of these publications studied animals from the Weddell Sea (Blix & Nordoy 2007). Unlike the other ice-breeding seals (i.e. Weddell, Leopard, and Crabeater seals), Ross seals are known to forage pelagically most of the year. We deployed satellite-linked tracking devices in the eastern Weddell Sea on 13 Ross seals (n = 11 in 2016; n = 2 in 2018), of which 6 of these devices also recorded diving behaviour. We combined this data with already published satellite telemetry and diving data from ten individuals tracked during 2001 (Blix & Nordoy 2007). For each individual’s track, we simulated a set of pseudo-tracks that allowed a presence-availability habitat modelling approach, which estimates an animal’s habitat preference. We modelled these tracks as a response to several remotely sensed environmental variables by means of ensemble models of boosted regression trees and random forests. Preliminary results suggest that Ross seals forage at the southern boundary of the Polar Front and avoid areas of high eddy activity. During the winter months, some individuals will forage at the edge of the sea-ice, while others remain to forage within the vicinity of Bouvetøya. Most individuals traversed the Southern Ocean 2-3 times during a single year, before returning to Antarctica in January for their annual moult. Ross seals dived on average to 100-300 m deep with a deepest dive of 792 m recorded. Ross seals present a unique opportunity to sample the water masses close to the Antarctic pack-ice edge and do cross-sections of the Southern Ocean year round – especially during winter when ships and other autonomous sampling platforms cannot enter the ice.

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Conference (Talk)
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5th South African Marine Mammal Colloquium, 20 Aug 2018 - 23 Aug 2018, Port Elizabeth, Souh Africa.
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Wege, M. , Bornemann, H. , Lubcker, N. , Postma, M. and Bester, M. N. (2018): Habitat use and diet of the Ross seal in the eastern Weddell Sea , 5th South African Marine Mammal Colloquium, Port Elizabeth, Souh Africa, 20 August 2018 - 23 August 2018 .

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