Distribution of cetacean species at a large scale - Connecting continents with the Macaronesian archipelagos in the eastern North Atlantic

Aim To describe distribution patterns and species richness of cetaceans along a wide geographical range using occurrence data coupled with survey effort, from poorly studied oceanic areas. Specific objectives were to compare species richness and relative abundances among sub-regions and to describe the distribution of each species. Location Eastern North Atlantic. Time period 2012-2017. Major taxa studied Cetacea. Methods Cetacean monitoring was performed by dedicated observers from cargo ships, used as platforms of opportunity, along routes between Iberian Peninsula, Macaronesia and north-western Africa. We mapped relative abundance (encounter rates), survey effort and species richness. We examined the dependence of the number of sightings and species richness on survey effort. The area was divided into sub-regions (according to the Exclusive Economic Zones and international waters), and relative abundances of the eight most frequently sighted species, as well as species richness, were compared among them. In addition, we describe the distribution of each species in relation to sea depth, distance to coast, latitude and longitude. Results A total of 1,989 sightings were logged, and 26 cetacean species were identified. Species richness and relative abundances of the eight most common species differed substantially between sub-regions. Common and bottlenose dolphins distributed in shallow coastal waters contrasting with the oceanic distribution ofStenelladolphins. Cuvier's beaked whale and minke whale had similar distributions. Pilot and sperm whales were distributed in southern waters. Main conclusions A considerable amount of survey effort was needed to attain reliable estimates of species richness. In less surveyed areas, species richness and abundance are likely to be underestimated. The offshore waters presented high species richness and several hotspots of cetacean abundance. This work provides new knowledge on cetacean distribution at a large scale in the eastern North Atlantic, relevant to future conservation management.