Abstract
The crabeater seal (Lobodon carcinophaga) is the most abundant Antarctic seal and inhabits the circumpolar pack ice zone of the Southern Ocean. Until now, information on important environmental factors affecting its distribution as well as on foraging behaviour is limited. In austral summer 1998, 12 crabeater seals of both sexes and different age classes were equipped with satellite-linked dive recorders at Drescher Inlet (72.85°S, 19.26°E), eastern Weddell Sea. To identify suitable habitat conditions within the Weddell Sea, a maximum entropy (Maxent) modelling approach was implemented. The model revealed that the eastern and southern Weddell Sea is especially suitable for crabeater seals. Distance to the continental shelf break and sea ice concentration were the two most important parameters in modelling species distribution throughout the study period. Model predictions demonstrated that crabeater seals showed a dynamic response to their seasonally changing environment emphasized by the favoured sea ice conditions. Crabeater seals utilized ice-free waters substantially, which is potentially explained by the comparatively low sea ice cover of the Weddell Sea during summer 1998. Diving behaviour was characterized by short (>90 % = 0–4 min) and shallow (>90 % = 0–51 m) dives. This pattern reflects the typical summer and autumn foraging behaviour of crabeater seals. Both the distribution and foraging behaviour corresponded well with the life history of the Antarctic krill (Euphausia superba), the preferred prey of crabeater seals. In general, predicted suitable habitat conditions were congruent with probable habitats of krill, which emphasizes the strong dependence on their primary prey.
Highlights
The crabeater seal (Lobodon carcinophaga) is by far the most abundant Antarctic pinniped species comprising an estimated population size between 5 and 7 million individuals, of which a major portion is found in the Weddell Sea (Erickson and Hanson 1990; Bester and Odendaal 2000; Forcada et al 2012; Southwell et al 2012)
We investigated the influence of certain environmental variables on the distribution and movements of crabeater seals in the Weddell Sea by applying a presence-only habitat modelling approach called maximum entropy (Maxent)
Of the 15 SDRs that were deployed on crabeater seals, 12 provided extended transmission periods required for the modelling approach
Summary
The crabeater seal (Lobodon carcinophaga) is by far the most abundant Antarctic pinniped species comprising an estimated population size between 5 and 7 million individuals, of which a major portion is found in the Weddell Sea (Erickson and Hanson 1990; Bester and Odendaal 2000; Forcada et al 2012; Southwell et al 2012). Reliable abundance estimates are difficult to obtain, since crabeater seals inhabit the hardly accessible Antarctic pack ice zone (Joiris 1991; Bester et al 2002; Ackley et al 2003; Southwell et al 2012). Their life cycle is tightly coupled to the availability of sea ice that they occupy for breeding, mating, moulting and resting (Siniff et al 1979; Bengtson and Cameron 2004; Southwell 2004). This may become increasingly important with regard to the predicted decrease of sea ice cover in the Southern Ocean (Siniff et al 2008; Forcada et al 2012)
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