Adjustment of diving behaviour with prey encounters and body condition in a deep diving predator: the Southern Elephant Seal

Joffrey Jouma'A (1) , Yves Le Bras (1) , Gaëtan Richard (1) , Jade Vacquié-Garcia (1) , Baptiste Picard (1) , Nory El Ksabi (1) , Christophe Guinet (1)

1 CEBC - Centre d'Études Biologiques de Chizé - UMR 7372

1. Optimal diving models have been developed to investigate how air-breathing predators should adjust their diving behaviour to optimize their foraging efficiency. Using time-depth recorders and 3D accelerometers, we addressed this question on six free-ranging Southern Elephant Seal (SES) females equipped on Kerguelen Island. 2. We hypothesize that seals would initially increase their foraging time with distance to the foraging patches before reducing it for physiological reasons, regardless of the prey encountered. We expect that SES spends more time at depths where more Prey Catch Attempts (PCA) occur, that is at the bottom. We also hypothesize that bottom time should be related to both the seal body density and the swimming effort dedicated to catching prey, as we expect seals to be more active when catching prey. Finally, because oxygen is acquired at the surface only, we expect that recovery times increase with the duration of the previous dives. 3. A total of 726% of PCA detected by accelerometer occurred at the bottom of the dive. At shallow depths (<300 m), seals spent more time at the bottom in dives where PCA occurred compared to non-PCA dives. At deeper depths, SES had shorter bottom times in PCA dives due to higher swimming effort. When only dives associated with PCA were considered, the time spent at the bottom increased with the number of PCA. In addition, the closer the seal was to neutral buoyancy, the longer was the bottom duration. Body density, that is buoyancy, was found to be a critical factor in controlling variations in the dive duration through the swimming effort to access the prey at the bottom of the dive. Finally, post-dive surface intervals were related to the duration and swimming effort of the previous dive. 4. This study reveals how a marine top predator adjusts the time spent at the bottom depending on its body density, prey encounter rate and prey accessibility. It also highlights that using the duration of the foraging phase as a proxy of foraging success can be seriously misleading in SES. Finally, the need to use an energetic approach with bio-logging technology to study behavioural ecology is emphasized.

Mots clés: optimal diving theory; marine mammal; foraging behaviour; bio-logging; buoyancy

Domaines: Sciences de l'environnement

Joffrey Jouma'A, Yves Le Bras, Gaëtan Richard, Jade Vacquié-Garcia, Baptiste Picard, et al.. Adjustment of diving behaviour with prey encounters and body condition in a deep diving predator: the Southern Elephant Seal. Functional Ecology, 2016, 30, pp.636-648. ⟨10.1111/1365-2435.12514⟩. ⟨hal-01199854⟩