| Summary: | Cetacean sighting data were collected on a research cruise carried out in autumn season (27.10-02.11.2007) in the western Black Sea between Istanbul (Turkey) and Constanta (Romania) and vice versa. This research cruise was conducted with a 32-m research vessel R/V YUNUS-S in the international waters. Average speed of the vessel was 10 nautical miles/h. At each sighting of cetaceans, species, numbers of animals, location (coordinates), time, behaviour of animals were recorded. During the survey, totally 417 nm was covered and 33 h of effort was made. The aim of the preliminary study was understanding the size and distribution of dolphin population in the western Black Sea. During the study, totally 16 sightings (91 individuals) of three species; common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus) and harbour porpoise (Phocoena phocoena) were recorded. Number of individuals and number of sightings are 61 common dolphins in eight, 29 bottlenose dolphin in seven, and a harbour porpoise in one observation. The overall encounter rate was 3.83 sightings/100nmiles. Common dolphin was the most often observed species (50%), followed by the bottlenose dolphin (44%), and harbour porpoise (6%).
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