Southern elephant seal, samplers of marine resources distribution

• Main Author: Le Bras, Yves
• 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), Université de La Rochelle, Christophe Guinet
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2017
• Subjects: Southern elephant seals; Bio-logging; Myctophids; Southern ocean; Fine scale; Diving behaviour; Predator-prey interactions; Eléphant de mer austral; Myctophidés; Océan austral; Fine échelle; Comportement de plongée; Interactions prédateur-proies; [SDV.SA]Life Sciences [q-bio]/Agricultural sciences; Southern Ocean; Austral; Elephant Seal; Elephant Seals; Southern Elephant Seal; Southern Elephant Seals
• Online Access: https://theses.hal.science/tel-01906055; https://theses.hal.science/tel-01906055/document; https://theses.hal.science/tel-01906055/file/thesis_Yves_LE_BRAS_final2.pdf

Because of the remoteness and harsh meteorological conditions of the southern ocean, data sampling is more costly in this area. Use of electronic devices attached to marine predators (Bio-logging), such as southern elephant seals, has emerged as an interesting approach to cope with this problem. Female southern elephant seals primarily feed on small bioluminescent meso-pelagic fishes called myctophids. Because of their large abundance and of their diel vertical migration behaviour, these organisms have a major ecological importance in the southern ocean. However, the spatial distribution of the elephant seals prey, as well as the bio-physical processes affecting the dynamics of this distribution, are still poorly known. This thesis intends to investigate this issue using high sampling frequency bio-logging data collected by female southern elephant seals. This work is based on the analysis of elephant seals diving behaviour in relation to changes in the occurrence of prey encounter events detected from acceleration data. Our results suggest that (1) prey abundance decreases with depth and that their distribution tend to standardize, (2) prey are distributed into layers, (3) vertical constraints could modulate the prey density by acting on the vertical spread of these layers, (4) prey items are well dispersed in comparison to the perception range of elephant seals, and finally (5) that meso-scale eddies, notably their edges, play a structuring role in the prey distribution during the austral summer. Du fait de l’isolement géographique de l’océan austral et des conditions météorologiques qui y règnent, la collecte de données océanographiques par les moyens conventionnels est particulièrement couteuse dans cette région du globe. Pour pallier à ces difficultés, l’utilisation d’enregistreurs électroniques embarqués sur des prédateurs marins, et notamment sur les éléphants de mer austraux, s’est révélée être une approche intéressante. Les femelles éléphants de mer s’alimentent en grande partie de petits poissons ...