MODELISATION DES STRATEGIES D'APPROVISIONNEMENT DES ELEPHANTS DE MER AUSTRAUX - INFLUENCE DE LA VARIABILITE DE LA PRODUCTION PRIMAIRE ET DES CONDITIONS OCEANOGRAPHIQUES PHYSIQUES

• Main Author: Dragon, Anne-Cécile
• Other Authors: Centre d'études biologiques de Chizé (CEBC), Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie - Paris VI, Christophe GUINET([e-mail])
• Format: Thesis
• Language: French
• Published: HAL CCSD 2011
• Subjects: envir; geo; Austral; Southern Ocean; Elephant Seals; Southern Elephant Seals
• Online Access: https://tel.archives-ouvertes.fr/tel-00660213/file/Dragon_Anne_Cecile.pdf; https://tel.archives-ouvertes.fr/tel-00660213

In the polar frontal zone of the Southern Ocean, fronts and mesoscale eddies were shown to have a significant impact in structuring and enhancing the primary productivity. They are therefore likely to influence the spatio-temporal structure of prey fields and play a key role on the creation of preferred foraging regions for oceanic top-predators. The optimal foraging theory predicts that predators should adjust their movements' behaviour in relation to prey density. While crossing areas with sufficient prey density, it is thought that those predators would change their behaviour by decreasing their displacement speed and increasing their turning frequency. With southern elephant seals telemetric data, our aims were to (1) determine the best methodology to estimate foraging effort and success along tracks and dives of the seals and (2) investigate the changes in fine scale foraging mouvement and diving behaviour of southern elephant seals in relation with local oceanographic conditions. Southern elephant seals were shown to display area-restricted search to optimally exploit their environment. The most favourable foraging zones were related to the presence of both cyclonic and anti-cyclonic eddies. Elephant seals used the centre and edges of cyclonic eddies but only the edges of the anti-cyclonic ones and adjusted their diving behaviour accordingly. Within dives, thermal characteristics of the water column explained the seals foraging behaviour. These fine and medium scales interactions characterise the prey fields distributions from which elephant seals depend on. Finally, the spatio-temporal repartition of favourable foraging zones was thus obtained which will help us to understand the foraging strategies that have been optimised along time by this population of toppredators in this complex and dynamic environment. Dans la zone interfrontale de l'Océan Austral, de grandes structures agencent la distribution spatiotemporelle des blooms phytoplanctoniques. Ces structures, à grande (fronts) et moyenne ...