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

Abstract

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 of Stenella dolphins. 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.

Predicting Cetacean Distributions in the Eastern North Atlantic to Support Marine Management

“…GAM models are likely to perform less well, with lower explained deviances, if different populations or ecotypes with varying habitat preferences or habitat uses are being included in the analysis. This may have been the case for the models obtained for the bottlenose dolphin, which has both coastal and oceanic ecotypes in the area (e.g., Fernández et al, 2011;Correia et al, 2020). Nevertheless, clear habitat preferences and areas of highly suitable habitat were found.…”

“…There were no campaigns in January or April. For spatiotemporal details on the sampled transects, see Correia et al (2020).…”

“…In the eastern North Atlantic, within the area encompassing the Iberian and northwestern (NW) African coasts and the Macaronesia, 36 species of cetaceans have been recorded, with the eight most frequently sighted representing all of the main guilds of cetaceans: small dolphins (bottlenose dolphins Tursiops truncatus, common dolphins Delphinus delphis, striped dolphins Stenella coeruleoalba, and Atlantic spotted dolphins Stenella frontalis), large dolphins (pilot whale Globicephala sp. ), beaked whales (Cuvier's beaked whales Ziphius cavirostris), sperm whales (Physeter macrocephalus) and baleen whales (minke whales Balaenoptera acutorostrata) (Correia et al, 2020). This is an area with a wide latitudinal and longitudinal range, encompassing substantial habitat variability (Mason, 2009;Sala et al, 2013).…”

“…This is an area with a wide latitudinal and longitudinal range, encompassing substantial habitat variability (Mason, 2009;Sala et al, 2013). The composition of cetacean community species profiles varies among sub-regions (Correia et al, 2020), but cetaceans move and migrate across the entire area (Alves et al, 2018a;Valente et al, 2019). Therefore, to fully understand the habitat requirements of cetacean species in this area, distribution patterns need to be analysed at the basin-scale.…”

“…In this study, we aimed to relate habitat characteristics to the distribution of the eight most frequently sighted cetacean species within the eastern North Atlantic, by using ecological niche models, at basin-scale, with data collected between 2012 and 2017 from OPOs along long-distance routes (CETUS Project; Correia et al, 2019a). A description of the spatial and temporal distributions of all cetacean species sighted is presented in Correia et al (2020). Here, we applied two different modelling techniques, thus benefitting from the strengths of each in a complementary approach: a presence/pseudo-absence approach accounting for sampling effort using Generalised additive models (GAMs) to analyse cetacean-habitat relationships, and a presence/background approach including a larger dataset (all presence points) using Maximum entropy models (Maxent) to forecast habitat suitability for the eight cetacean species over the entire study area.…”