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Abstract
AbstractAimTo 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.LocationEastern North Atlantic.Time period2012–2017.Major taxa studiedCetacea.MethodsCetacean 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.ResultsA 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 conclusionsA 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.
Highlights
Knowledge on distribution patterns of marine species is essential for efficient marine management and biodiversity conservation
We provide a descriptive analysis of spatial and temporal patterns in cetacean distribution and species richness, using effort-based data collected within the eastern North Atlantic (ENA), from 2012 to 2017, with high survey effort in the open ocean
We identified areas with the highest relative abundance and species richness, which may be priority areas for future research and conservation efforts, and compared species richness and relative abundances among sub-regions (Iberian Peninsula, Azores, Madeira, Canaries, Cape Verde, north-western Africa and international waters)
Summary
Knowledge on distribution patterns of marine species is essential for efficient marine management and biodiversity conservation. Observation platforms of opportunity (OPOs) have been widely used to monitor cetacean presence, allowing the sampling of remote areas, such as the high seas, over long periods of time This methodology has limitations, for example heterogeneous effort conditioned by the routes, schedules and logistics of the platform of opportunity, usually with a restricted spatial coverage of the study area. It is frequently the most cost-effective method to generate baseline data, allowing the collection of valuable data that would otherwise be difficult or impossible to obtain (Aïssi et al, 2015; Alves, Ferreira, et al, 2018; Correia et al, 2015; Evans, Hammond, 2004; Kiszka et al, 2007; Morgado, Martins, Rosso, Moulins, & Tepsich, 2017; Moura et al, 2012; Tobeña et al, 2016; Viddi et al, 2010). We identified areas with the highest relative abundance and species richness, which may be priority areas for future research and conservation efforts, and compared species richness and relative abundances among sub-regions (Iberian Peninsula, Azores, Madeira, Canaries, Cape Verde, north-western Africa and international waters)
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