| Summary: | 265 pages Cetacean species assume very important roles for the conservation of marine ecosystems as keystone, umbrella, biodiversity indicators, sentinel and flagship species. However, conservation of cetaceans is hindered by the lack of information on their occurrence and distribution patterns. The most important knowledge gaps are in high-seas where research effort is limited given the complex and expensive logistics of offshore surveys. To overcome this challenge, reseachers have been relying on observation platforms of opportunity (OPOs) to collect data in more remote, less accessible areas. In the eastern North Atlantic (ENA), a great diversity of cetacean species has been recorded but occurrence records are mostly restricted to coastal areas. Data on cetacean occurrence collected between 2012 to 2017 abroad OPOs was used to study cetacean distribution and habitat within the ENA, in the area delimited by the coasts of the Iberian Peninsula and northwest Africa and the archipelagos of Macaronesia. A great biodiversity of cetacean species was reported in the high seas. Eight species were recorded more often: Delphinus delphis, Stenella frontalis, Stenella coeruleoalba, Tursiops truncatus, Ziphius cavirostris, Globicephala sp., Physeter macrocephalus and Balaenoptera acutorostrata, with D. delphis being the most frequently sighted. Ecological niche modelling was conducted taking into account detectability factors, spatiotemporal variables, oceanographic processes and topographic structures: D. delphis preferred areas located in the north and in coastal shallow waters, mostly in the Iberian Peninsula and the Azores archipelago; Stenella sp. presented a wide ecological niche, occurring mostly in oceanic waters and in the archipelagos; T. Tursiops was associated with continental platforms; Z. cavirostris preferred northern oceanic waters and was associated with seamounts; Globicephala sp. and P. macrocephalus occurred further south; and B. acutorostrata preferred northern oceanic waters in areas closer to the ...
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