Trophic ecology of two sympatric seal species at the limit of their distribution range

• Main Author: Planque, Yann
• Other Authors: Centre d'Études Biologiques de Chizé - UMR 7372 (CEBC), La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE), Université de La Rochelle, Florence Caurant, Cécile Vincent
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2021
• Subjects: Diet; Foraging behaviour; Interspecific competition; Intraspecific variability; Spatial analysis; Isotopic niche; Coexistence; Harbour seal; Phoca vitulina; Grey seal; Halichoerus grypus; Marine top predators; Pinnipeds; GPS/GSM tags; Régime alimentaire; Comportement de chasse; Compétition interspécifique; Variabilité intraspécifique; Analyse spatiale; Niche isotopique; Phoque veau-marin; Phoque gris; Prédateurs supérieurs marins; Pinnipèdes; Balises GPS/GSM; [SDV.SA]Life Sciences [q-bio]/Agricultural sciences; Phoques; harbour seal; veau marin
• Online Access: https://theses.hal.science/tel-03720984; https://theses.hal.science/tel-03720984/document; https://theses.hal.science/tel-03720984/file/2021PLANQUE181428.pdf

Harbour seal (Phoca vitulina) and grey seal (Halichoerus grypus) are two sympatric marine mammal species that are increasingly considered as potential competitors, especially at their European core distributions. The objective of this PhD was to study the foraging strategies and trophic ecology of these species at the limit of their range (Baie de Somme, Eastern English Channel, France), and to investigate the hypothesis of potential interspecific competition. Biotelemetry devices were fitted on 49 individuals to document their movements and dives at sea.The analysis of surface locations and diving behaviour, completed recently by the detection of Prey Capture Attempts (accelerometry), allowed for a better understanding of the two seal species’ foraging strategies and improved the detection of their foraging areas. Trophic niches of the two seal species were then characterised with the analysis of diet, stable isotopes (in the whiskers of the same captured individuals), and foraging areas. A high interspecific trophic overlap was identified between these niches, resulting from the consumption of benthic flatfish in coastal areas, and we suggest that it provides here the basis for potential competition between both species. This study also showed the key role of individual foraging strategies on the ecological conclusions at the scale of the species/sub-population, including that the potential competition may be due to some individual grey seal strategies. Continuing these studies is essential to detect any potential ecological changes that could be trophically-induced. Le phoque veau-marin (Phoca vitulina) et le phoque gris (Halichoerus grypus), deux espèces sympatriques de mammifères marins, sont de plus en plus considérés comme des compétiteurs potentiels, et ce plus particulièrement au cœur de leur distribution européenne. L’objectif de cette thèse est d’étudier les stratégies de chasse et l’écologie trophique de ces espèces en limite de leur aire de distribution (baie de Somme, Manche Est, France), et ...