How elephant seals (Mirounga leonina) adjust their fine scale horizontal movement and diving behaviour in relation to prey encounter rate

• Published in: PLOS ONE
• Main Authors: Le Bras, Yves, Jouma'A, Joffrey, Picard, Baptiste, 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: [SDE]Environmental Sciences; Southern Ocean; Elephant Seal; Elephant Seals; Mirounga leonina; Southern Elephant Seal
• Online Access: https://hal.science/hal-01496986; https://doi.org/10.1371/journal.pone.0167226

International audience Understanding the diving behaviour of diving predators in relation to concomitant prey distributioncould have major practical applications in conservation biology by allowing theassessment of how changes in fine scale prey distribution impact foraging efficiency andultimately population dynamics. The southern elephant seal (Mirounga leonina, hereafterSES), the largest phocid, is a major predator of the southern ocean feeding on myctophidsand cephalopods. Because of its large size it can carry bio-loggers with minimal disturbance.Moreover, it has great diving abilities and a wide foraging habitat. Thus, the SES is a wellsuited model species to study predator diving behaviour and the distribution of ecologicallyimportant prey species in the Southern Ocean. In this study, we examined how SESs adjusttheir diving behaviour and horizontal movements in response to fine scale prey encounterdensities using high resolution accelerometers, magnetometers, pressure sensors andGPS loggers. When high prey encounter rates were encountered, animals responded by (1)diving and returning to the surface with steeper angles, reducing the duration of transit divephases (thus improving dive efficiency), and (2) exhibiting more horizontally and verticallysinuous bottom phases. In these cases, the distance travelled horizontally at the surfacewas reduced. This behaviour is likely to counteract horizontal displacement from water currents,as they try to remain within favourable prey patches. The prey encounter rate at thebottom of dives decreased with increasing diving depth, suggesting a combined effect ofdecreased accessibility and prey density with increasing depth. Prey encounter rate alsodecreased when the bottom phases of dives were spread across larger vertical extents ofthe water column. This result suggests that the vertical aggregation of prey can regulateprey density, and as a consequence impact the foraging success of SESs. To our knowledge,this is one of only a handful of studies showing how the ...