DEPREDATION PAR LES ORQUES (ORCINUS ORCA) ET LES CACHALOTS (PHYSETER MACROCEPHALUS) SUR LES PALANGRIERS A LA LEGINE AUSTRALE DANS LA ZEE DE L'ARCHIPEL DE CROZET

• Main Author: Tixier, Paul
• Other Authors: Centre d'Études Biologiques de Chizé (CEBC), Institut National de la Recherche Agronomique (INRA)-Centre National de la Recherche Scientifique (CNRS), Université Aix-Marseille II, Christophe GUINET([e-mail])
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2012
• Subjects: DEPREDATION; KILLER WHALE; MITIGATION; SOCIAL ORGANIZATION; DEMOGRAPHY; FEEDING ECOLOGY; CONSERVATION; [SDE]Environmental Sciences; Orques; Killer Whale; Orca; Orcinus orca; Patagonian Toothfish; Physeter macrocephalus; Killer whale
• Online Access: https://theses.hal.science/tel-00910893; https://theses.hal.science/tel-00910893/document; https://theses.hal.science/tel-00910893/file/TIXIER_Paul.pdf

Over the last 50 years, fisheries have undergone a major decline worldwide. With an increased competition for resource, depredation (i.e. removal of catches on fishing gear) has recently become a major case of conflict between humans and marine predators. In this study I focused on the depredation on Patagonian toothfish fisheries by killer and sperm whales in the Crozet EEZ. The first part of the study aimed at assessing the socio-economic consequences of this issue. Killer and sperm whales have interacted with 43.3% and 57.5% of longlines (n = 5 438) respectively from 2003 to 2010. Killer whales, alone or co-occurring with sperm whales were responsible for an estimated loss of 926 ± 76 tons of toothfish over that period, which represents 17.7% of the total catch. Three operational factors were identified as influencing significantly depredation levels: i) the use of short longlines (<5000m) in absence of killer whales, ii) the displacement of vessels on distances >75 km to leave the whales behind and iii) the use of longline hauling speed > 50 ham.min-1. The second aim of the study was to investigate the consequences of depredation on the Crozet killer whale population. The long term monitoring of individuals showed divergent demographic trajectories related to the depredation level of matrilines. During the 1990s, matrilines interacting with fisheries have undergone a high mortality due to lethal interactions with illegal fishing vessels using explosives to repel the whales. Since 2003 and the end of illegal fisheries, martilines interacting the most with fisheries have now clear demographic advantages with better survival and reproduction that other matrilines, suggesting the benefits of depredation. As depredation is a growing issue in the world, this study has great implications, on one hand because it involves a productive collaboration between fishermen, government and researchers, and on the other hand because it provides accurate insights on conservation priorities of such an issue. C'est ...