Distribution and density estimates of cetaceans along the midAtlantic Ridge during summer 2004

During 4 June-2 July 2004, the Norwegian R/V G.O. Sars conducted a multi-disciplinary survey along mid-Atlantic Ridge (MAR) from Reykjanes to north of Azores. This provided first systematic information on MAR cetacean populations. Using naked eye or 7350 hand-held binoculars, observers searched in 140° arc centred ships’ heading. Eleven species and 10 other taxonomic groups were identified 2,321km transect effort. The sei whale (Balaenoptera borealis) sperm (Physeter macrocephalus) most commonly sighted (53 48 sightings, respectively). There 12 sightings fin (B. physalus). 26, 13 respectively common dolphin (Delphinus delphis), pilot (Globicephala sp.) striped (Stenella coeruleoalba). Density estimates ranged 0.018 0.238 animals km–2. precision (CV) was low, ranging 40% 61%. Species distribution varied south; highest aggregations baleen whales at Charlie Gibbs Fracture Zone (CGFZ). Sperm also observed CGFZ as well this area. Pilot Atlantic white-sided dolphins (Lagenorhynchus acutus) mainly cold (5-16°C) less saline (34.6-35.8‰) water masses Ridge. Conversely, south areas with warmer (12-22°C) more (34.8-36.7‰) surface temperatures.