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Some like it cold: southern elephant seal dive behaviour responses to changes in water temperature

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McIntyre, T. , Ansorge, I. J. , Bester, M. N. , Bornemann, H. , Plötz, J. and Tosh, C. A. (2010): Some like it cold: southern elephant seal dive behaviour responses to changes in water temperature , IPY Oslo science conference, Oslo, NorwayJun. 2010. .
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Abstract:

Satellite-relay data loggers (SRDLs) were deployed on southern elephant seals hauled out at Marion Island as part of the International Polar Year project, Marine Mammal Exploration of the Oceans Pole to Pole (MEOP). We describe the dive behaviour responses of one male elephant seal to changes in oceanographic conditions during two post-moult migrations. The seal concentrated his diving activity in a small area (<200 square km) in close proximity to the Prince Edward Islands during both migrations. The restricted area utilised by the animal allowed for temporal comparisons in dive behaviour and excluded potential effects associated with changes in geographic position. The SRDLs transmitted a total of 16806 temperature points (1265 temperature profiles). Mean monthly in situ surface temperatures were significantly correlated with remotely sensed (MODIS) SST data for the study area. Surface and subsurface temperatures in the study area remained stable throughout both migrations, but were colder in October 2006 due to an intrusion of a cold, anti-cyclonic feature. Dive depths obtained by the seal were similar between years, though dives were longer during 2007. The differences in dive durations between years were a result of the seal spending more time at depths between 300m and 500m during 2007, when compared to 2006. During the colder period of October 2006, the instrumented seal performed shallower and shorter dives when compared to the rest of the migration period. The seal spent relatively more time near the maximum depths of dives during this period, indicating a likely increase in foraging effort. Our results highlight a link between oceanographic data obtained from seal-borne instrumentation and dive behaviour of elephant seals. This is even more pronounced by deploying tags to the same individual over several consecutive years, which excludes interspecific effects in multiyear comparisons. We furthermore suggest that elephant seals alter their dive behaviour on a fine scale to maximise foraging benefits associated with variations in oceanographic conditions, particularly in proximity to mesoscale features.

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