title: Co-Occurrence and Habitat Use of Fin Whales, Striped Dolphins and Atlantic Bluefin Tuna in the Northwestern Mediterranean Sea.
abstract: Different dolphin and tuna species have frequently been reported to aggregate in areas of high frontal activity, sometimes developing close multi-species associations to increase feeding success. Aerial surveys are a common tool to monitor the density and abundance of marine mammals, and have recently become a focus in the search for methods to provide fisheries-independent abundance indicators for tuna stock assessment. In this study, we present first density estimates corrected for availability bias of fin whales (Balaenoptera physalus) and striped dolphins (Stenella coeruleoalba) from the Golf of Lions (GoL), compared with uncorrected estimates of Atlantic bluefin tuna (ABFT; Thunnus thynnus) densities from 8 years of line transect aerial surveys. The raw sighting data were further used to analyze patterns of spatial co-occurrence and density of these three top marine predators in this important feeding ground in the Northwestern Mediterranean Sea. These patterns were investigated regarding known species-specific feeding preferences and environmental characteristics (i. e. mesoscale activity) of the survey zone. ABFT was by far the most abundant species during the surveys in terms of schools and individuals, followed by striped dolphins and fin whales. However, when accounted for availability bias, schools of dolphins and fin whales were of equal density. Direct interactions of the species appeared to be the exception, but results indicate that densities, presence and core sighting locations of striped dolphins and ABFT were correlated. Core sighting areas of these species were located close to an area of high mesoscale activity (oceanic fronts and eddies). Fin whales did not show such a correlation. The results further highlight the feasibility to coordinate research efforts to explore the behaviour and abundance of the investigated species, as demanded by the Marine Strategy Framework Directive (MSFD).
authors.affiliation: IFREMER (Institut Français de Recherche pour l'Exploitation de la MER), Resarch Unit Marbec (Marine Biodiversity, Exploitation and Conservation), Sète, France.
authors.forename: Robert Klaus
authors.initials: RK
authors.lastname: Bauer
authors.affiliation: IFREMER (Institut Français de Recherche pour l'Exploitation de la MER), Resarch Unit Marbec (Marine Biodiversity, Exploitation and Conservation), Sète, France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Fromentin
authors.affiliation: IRD (Institut de Recherche pour le Développement), Resarch Unit Marbec (Marine Biodiversity, Exploitation and Conservation), Sète, France.
authors.forename: Hervé
authors.initials: H
authors.lastname: Demarcq
authors.affiliation: IFREMER (Institut Français de Recherche pour l'Exploitation de la MER), Resarch Unit Marbec (Marine Biodiversity, Exploitation and Conservation), Sète, France.
authors.forename: Blandine
authors.initials: B
authors.lastname: Brisset
authors.affiliation: IFREMER (Institut Français de Recherche pour l'Exploitation de la MER), Resarch Unit Marbec (Marine Biodiversity, Exploitation and Conservation), Sète, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Bonhommeau
mesh_terms: D000818:Animals; D017753:Ecosystem; D050617:Fin Whale; D008522:Mediterranean Sea; D062206:Spatial Analysis; D050706:Stenella; D011795:Surveys and Questionnaires; D014413:Tuna