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Variation in body condition during the post-moult foraging trip of southern elephant seals and its consequences on diving behaviour.

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posted on 2014-07-15, 00:00 authored by Gaetan Richard, J Vacquié-Garcia, J Jouma'a, B Picard, A Génin, John ArnouldJohn Arnould, F Bailleul, C Guinet
Mature female southern elephant seals (Mirounga leonina) come ashore only in October to breed and in January to moult, spending the rest of the year foraging at sea. Mature females may lose as much as 50% of their body mass, mostly in lipid stores, during the breeding season due to fasting and lactation. When departing to sea, post-breeding females are negatively buoyant, and the relative change in body condition (i.e. density) during the foraging trip has previously been assessed by monitoring the descent rate during drift dives. However, relatively few drift dives are performed, resulting in low resolution of the temporal reconstruction of body condition change. In this study, six post-breeding females were equipped with time-depth recorders and accelerometers to investigate whether changes in active swimming effort and speed could be used as an alternative method of monitoring density variations throughout the foraging trip. In addition, we assessed the consequences of density change on the swimming efforts of individuals while diving and investigated the effects on dive duration. Both descent swimming speed and ascent swimming effort were found to be strongly correlated to descent rate during drift dives, enabling the fine-scale monitoring of seal density change over the whole trip. Negatively buoyant seals minimized swimming effort during descents, gliding down at slower speeds, and reduced their ascent swimming effort to maintain a nearly constant swimming speed as their buoyancy increased. One per cent of seal density variation over time was found to induce a 20% variation in swimming effort during dives with direct consequences on dive duration.

History

Journal

The Journal of Experimental Biology

Volume

217

Issue

14

Pagination

2609 - 2619

Publisher

Company of Biologists

Location

Cambridge, United Kingdom

eISSN

1477-9145

Language

eng

Publication classification

C Journal article; C1 Refereed article in a scholarly journal

Copyright notice

2014, Company of Biologists