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

• Published in: Functional Ecology
• Main Authors: Jouma'A, Joffrey, Le Bras, Yves, Richard, Gaëtan, Vacquié-Garcia, Jade, Picard, Baptiste, El Ksabi, Nory, Guinet, Christophe
• Other Authors: Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), Institut National de la Recherche Agronomique (INRA)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2016
• Subjects: optimal diving theory; marine mammal; foraging behaviour; bio-logging; buoyancy; [SDE]Environmental Sciences; Kerguelen; Kerguelen Island; Elephant Seal; Southern Elephant Seal
• Online Access: https://hal.science/hal-01199854; https://doi.org/10.1111/1365-2435.12514

International audience 1. Optimal diving models have been developed to investigate how air-breathing predatorsshould adjust their diving behaviour to optimize their foraging efficiency. Using time-depthrecorders and 3D accelerometers, we addressed this question on six free-ranging Southern ElephantSeal (SES) females equipped on Kerguelen Island.2. We hypothesize that seals would initially increase their foraging time with distance to theforaging 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 toboth the seal body density and the swimming effort dedicated to catching prey, as we expectseals to be more active when catching prey. Finally, because oxygen is acquired at the surfaceonly, 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. Atshallow depths (<300 m), seals spent more time at the bottom in dives where PCA occurredcompared to non-PCA dives. At deeper depths, SES had shorter bottom times in PCA divesdue to higher swimming effort. When only dives associated with PCA were considered, thetime spent at the bottom increased with the number of PCA. In addition, the closer the sealwas 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 theswimming effort to access the prey at the bottom of the dive. Finally, post-dive surface intervalswere 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 dependingon its body density, prey encounter rate and prey accessibility. It also highlights that usingthe duration of the foraging phase as a proxy of foraging success can be seriously ...