Winter use of sea ice and ocean water mass habitat by southern elephant seals: The length and breadth of the mystery

• Published in: Progress in oceanography 2015-09, Vol.137, p.52-68
• Main Authors: Labrousse, Sara, Vacquié-Garcia, Jade, Heerah, Karine, Guinet, Christophe, Sallée, Jean-Baptiste, Authier, Matthieu, Picard, Baptiste, Roquet, Fabien, Bailleul, Frédéric, Hindell, Mark, Charrassin, Jean-Benoit
• Format: Article
• Language: English
• Subjects: Antarctica; Environmental Sciences; Females; Forages; Males; Mathematical models; Sea ice; Seals; Strategy
• ISSN: 0079-6611; 1873-4472; 1873-4472
• DOI: 10.1016/j.pocean.2015.05.023

•Time-series of 35 elephant seal winter foraging trips to Antarctica were analyzed.•A high resolution dive behaviour dataset was used to predict foraging events.•The links between foraging and sea ice, hydrography and topography were quantified.•Foraging strategies depended on the sex of seals.•The foraging activity was associated with a number of oceanographic discontinuities. Understanding the responses of animals to the environment is crucial for identifying critical foraging habitat. Elephant seals (Mirounga leonina) from the Kerguelen Islands (49°20′S, 70°20′E) have several different foraging strategies. Why some individuals undertake long trips to the Antarctic continent while others utilize the relatively close frontal zones is poorly understood. Here, we investigate how physical properties within the sea ice zone are linked to foraging activities of southern elephant seals (SES). To do this, we first developed a new approach using indices of foraging derived from high temporal resolution dive and accelerometry data to predict foraging behaviour in an extensive, low resolution dataset from CTD-Satellite Relay Data Loggers (CTD-SRDLs). A sample of 37 post-breeding SES females were used to construct a predictive model applied to demersal and pelagic dive strategies relating prey encounter events (PEE) to dive parameters (dive duration, bottom duration, hunting-time, maximum depth, ascent speed, descent speed, sinuosity, and horizontal speed) for each strategy. We applied these models to a second sample of 35 seals, 20 males and 15 females, during the post-moult foraging trip to the Antarctic continental shelf between 2004 and 2013, which did not have fine-scale behavioural data. The females were widely distributed with important foraging activity south of the Southern Boundary Front, while males predominately travelled to the south-eastern part of the East Antarctica region. Combining our predictions of PEE with environmental features (sea ice concentration, water masses at the bottom phase of dives, bathymetry and slope index) we found higher foraging activity for females over shallower seabed depths and at the boundary between the overlying Antarctic Surface Water (AASW) and the underlying Modified Circumpolar Deep Water (MCDW). Increased biological activity associated with the upper boundary of MCDW, may provide overwintering areas for SES prey. Male foraging activity was strongly associated with pelagic dives within the Antarctic Slope Front where