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Population size and distribution of bottlenose dolphins (Tursiops truncatus) around the Lošinj and Cres archipelago

Bottlenose dolphins are the only regularly sighted cetaceans in Croatian waters. The Adriatic Dolphin Project (ADP) has monitored the resident bottlenose dolphin population of the Lošinj and Cres archipelago since 1987. Research has particularly focused on the socio-ecology of the population. Data was collected, using photo-identification of natural markings of individual dolphins, from May to October of the years 2001 and 2002. Population abundance was then estimated by using the software SOCPROG. The data was examined using analytical methods applied to minimise bias. It was found that a ‘ Mortality + Trend Model’ , was best fit to describe the population. The estimated number of dolphins with long-term markings accounted for 100 individuals (95% CI = 82.3 – 125.5, SE = 12.1). This is well below the IUCN’ s classification of ‘ critically endangered isolated populations’ with less than 250 individuals. The combined mortality, mark change and emigration rate was estimated at 0.02 % per year with a positive trend of 0.04 % per year. A lagged identification model also showed that during the field season individuals emigrated from, and re-immigrated back into the study area. These results also indicate that the study area is only part of the home range of the dolphins frequenting the area. It is essential to determine the population size and trend of animal species to establish and develop the implementation of management and conservation strategies for vulnerable populations. Further studies are necessary before an accurate status of the bottlenose dolphins in Croatian waters can be determined.

bottlenose dolphins; Tursiops truncatus; ecology; population size; Lošinj; Adriatic

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