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Presence and distribution of bottlenose dolphins (Tursiops truncatus) in the area between Dugi otok and Hvar islands (Croatia).

In previous decades the Adriatic Sea was known to be frequented by various species of Odontocetes, in particular the bottlenose dolphin (Tursiops truncatus), common dolphin (Delphinus delphis) and striped dolphin (Stenella coeruleoalba). However, at present the bottlenose dolphin appear to be the only species sighted regularly in the northern region of this sea. Little is known about the occurrence and distribution of Cetaceans in the Central Adriatic Sea, particularly on the bottlenose dolphin, with data available only from a long-term study (1987-present) in the Kvarnerić (northern Adriatic Sea). During the Summer 2002, a feasibility study was started in order to identify the best area for conducting a long term study within the chosen area. The aims of this study are: 1) to understand the occurrence, distribution and habitat use of bottlenose dolphin within the Kornati National Park and adjacent areas ; 2) to assess if photo-identified animals from the Kvarneric are extending their home range to areas of the Central Adriatic Sea, and ; 3) to outline suitable conservation measures for bottlenose dolphins frequenting this area, based on scientific knowledge and the comparison with the data from northern Adriatic Sea population segment. Standard research procedures included the collection of: navigation data ; environmental data ; photo-identification data ; and behavioural data. The study area was different in the four study's years, and different were the results. In general the sighting frequency in the study area was lower than the sighting frequency usually recorded in the Kvarneric. In four study's years 94 surveys were led, but taking into consideration only surveys carried out in good conditions they were 73, during which we have navigated for 482 hours, covering 2396 nm, monitoring an area of about 3800 Km2. During this period 34 sightings were done and 47 bottlenose dolphins were identified. No sightings of common or striped dolphins have been made.

bottlenose dolphin; Tursiops truncatus; Kornati; central Adriatic Sea

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