loading page

Trophic niche overlap between sympatric harbour seals (Phoca vitulina) and grey seals (Halichoerus grypus) at their Southern European limit range (Eastern English Channel)
  • +2
  • Yann Planque,
  • Jérôme Spitz,
  • Matthieu Authier,
  • Cécile Vincent,
  • Florence Caurant
Yann Planque
Centre d'Etudes Biologiques de Chizé
Author Profile
Jérôme Spitz
Centre d'Etudes Biologiques de Chizé
Author Profile
Matthieu Authier
Observatoire PELAGIS
Author Profile
Cécile Vincent
Centre d'Etudes Biologiques de Chizé
Author Profile
Florence Caurant
Centre d'Etudes Biologiques de Chizé
Author Profile


Competition between the sympatric harbour (Phoca vitulina) and grey seals (Halichoerus grypus) is thought to underlie some recent local declines of the former while the population of the latter remains stable or increases. A better understanding of the interactions between these two species is critical to elucidate current changes. This study aims at identifying and quantifying the niche overlap between harbour and grey seals at their Southern European limit range, in the baie de Somme (Eastern English Channel, France), in a context of exponential increase in the number of resident harbour seals and visiting grey seals. Isotopic niche overlap was quantified between both species using whisker δ13C and δ15N isotopic values, taking intra- and interindividual variability into account. Dietary overlap was quantified from scat contents using hierarchical clustering. A high degree of trophic niche overlap was identified between both species. The narrower isotopic niche of harbour seals was nested within that of grey seals (58.2% [CI95%: 22.7-100%] overlap). Six diet clusters were identified from scat content analysis. Two of them gathered most of harbour seals’ scats (85.5 % [80.3-90.2%]) and around half of grey seals’ ones (46.8% [35.1-58.4%]) that almost exclusively contained benthic flatfish. Consumption of this type of prey was identified here to be the root cause of trophic overlap. This highlighted the potential for competition between the two species at their Southern European limit range, linked to foraging on benthic flatfish, in coastal waters close to their haulout sites, especially during spring/summer. We suggest that (1) interspecific competition for prey could occur/increase in the future if the number of grey and harbour seals still increase and/or if flatfish supply decrease in this area, and (2) harbour seals would be disadvantaged in such a case if they do not adapt, as being specialised on flatfish at the colony scale.

Peer review status:IN REVISION

10 Nov 2020Submitted to Ecology and Evolution
11 Nov 2020Assigned to Editor
11 Nov 2020Submission Checks Completed
12 Nov 2020Reviewer(s) Assigned
03 Dec 2020Review(s) Completed, Editorial Evaluation Pending
07 Dec 2020Editorial Decision: Revise Minor