title: Variation in body condition during the post-moult foraging trip of southern elephant seals and its consequences on diving behaviour.
abstract: 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.
authors.affiliation: CEBC, UMR 7273 ULR-CNRS, 79360 Villiers en Bois, France.
authors.forename: Gaëtan
authors.initials: G
authors.lastname: Richard
authors.affiliation: CEBC, UMR 7273 ULR-CNRS, 79360 Villiers en Bois, France.
authors.forename: Jade
authors.initials: J
authors.lastname: Vacquié-Garcia
authors.affiliation: CEBC, UMR 7273 ULR-CNRS, 79360 Villiers en Bois, France.
authors.forename: Joffrey
authors.initials: J
authors.lastname: Jouma'a
authors.affiliation: CEBC, UMR 7273 ULR-CNRS, 79360 Villiers en Bois, France.
authors.forename: Baptiste
authors.initials: B
authors.lastname: Picard
authors.affiliation: CEBC, UMR 7273 ULR-CNRS, 79360 Villiers en Bois, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Génin
authors.affiliation: School of Life and Environmental Sciences, Deakin University, 221 Burwood Highway, Burwood, VIC 3125, Australia.
authors.forename: John P Y
authors.initials: JP
authors.lastname: Arnould
authors.affiliation: CEBC, UMR 7273 ULR-CNRS, 79360 Villiers en Bois, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Bailleul
authors.affiliation: CEBC, UMR 7273 ULR-CNRS, 79360 Villiers en Bois, France guinet@cebc.cnrs.fr.
authors.forename: Christophe
authors.initials: C
authors.lastname: Guinet
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology*; D001696:Biomechanical Phenomena; D001823:Body Composition; D004242:Diving / Q000502:physiology*; D005260:Female; D009792:Oceans and Seas; D046048:Seals, Earless / Q000502:physiology*; D013550:Swimming / Q000502:physiology*; D013686:Telemetry
keywords: Body condition; Buoyancy; Mirounga leonina; Speed; Swimming effort