Trophic niche overlap between sympatric harbour seals(Phoca vitulina) and grey seals (Halichoerus grypus) at thesouthern limit of their European range (Eastern EnglishChannel)

• Published in: Ecology and Evolution
• Main Authors: Planque, Yann, Spitz, Jérôme, Authier, Matthieu, Vincent, Cécile, Caurant, Florence
• 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), Observatoire pour la Conservation de la Mégafaune Marine (PELAGIS), LIttoral ENvironnement et Sociétés (LIENSs), La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2021
• Subjects: Foraging ecology; feeding strategies; pinnipeds; marine top predators; stableisotopes; diet content; [SDE]Environmental Sciences; harbour seal; Phoca vitulina
• Online Access: https://hal.science/hal-03108817; https://hal.science/hal-03108817/document; https://hal.science/hal-03108817/file/PEE11_2021.pdf; https://doi.org/10.1002/ece3.7739

International audience Sympatric harbour (Phoca vitulina) and grey seals (Halichoerus grypus) are increasinglyconsidered potential competitors, especially since recent local declines in harbourseal numbers while grey seal numbers remained stable or increased at their Europeancore distributions. A better understanding of the interactions between these speciesis critical for conservation efforts. This study aimed to identify the trophic nicheoverlap between harbour and grey seals at the southern limit of their Europeanrange, in the Baie de Somme (BDS, Eastern English Channel, France), where numbersof resident harbour seals and visiting grey seals are increasing exponentially. Dietaryoverlap was identified from scat contents using hierarchical clustering. Isotopic nicheoverlap was quantified using δ13C and δ15N isotopic values from whiskers of 18 individuals,by estimating isotopic standard ellipses with a novel hierarchical modeldeveloped in a Bayesian framework to consider both intraindividual variability andinterindividual variability. Foraging areas of these individuals were identified fromtelemetry data. The three independent approaches provided converging results, revealinga high trophic niche overlap due to consumption of benthic flatfish. Two dietclusters were dominated by either small or large benthic flatfish; these comprised85.5% [CI95%: 80.3%–90.2%]of harbour seal scats and 46.8% [35.1%–58.4%]of greyseal scats. The narrower isotopic niche of harbour seals was nested within that ofgrey seals (58.2% [22.7%–100%]overlap). Grey seals with isotopic values similar toharbour seals foraged in coastal waters close to the BDS alike harbour seals did, suggestingthe niche overlap may be due to individual grey seal strategies. Our findingstherefore provide the basis for potential competition between both species (foragingon benthic flatfish close to the BDS). We suggest that a continued increase in sealnumbers and/or a decrease in flatfish supply in this area could cause/amplify competitiveinteractions and have ...