Seasonal distribution and abundance of cetaceans within French waters- Part I: The North-Western Mediterranean, including the Pelagos sanctuary
Résumé
The biodiversity of the Mediterranean Sea is undergoing important changes. Cetaceans, as top predators, are an
important component of marine ecosystems. The seasonal distribution and abundance of several cetacean
species were studied with a large aerial survey over the North-Western Mediterranean Sea, including the
international Pelagos sanctuary, the largest Marine Protected Area (MPA) designed for marine mammals in the
Mediterranean. A total of 8 distinct species of cetaceans were identified, and their occurrence within the
sanctuary was investigated. Abundance estimates were obtained for three groups of species: the small
delphinids (striped dolphins mainly), the bottlenose dolphin and the fin whale. There was a seasonal variation
in striped dolphin abundance between winter (57,300 individuals, 95% CI: 34,500–102,000) and summer
(130,000, 95% CI: 76,800–222,100). In contrast, bottlenose dolphin winter abundance was thrice that of
summer. It was also the only species to exhibit any preference for the Pelagos sanctuary. Fin whale abundance
had the reverse pattern with winter abundance (1000 individuals, 95% CI: 500–2500) and summer (2500
individuals, 95% CI: 1500–4300), without any preference for the sanctuary. Risso's dolphins, pilot whales and
sperm whales did not exhibit strong seasonal pattern in their abundance. These results provide baseline
estimates which can be used to inform conservation policies and instruments such as the Habitats Directive or
the recent European Marine Strategy Framework Directive.