Common bottlenose dolphin (Tursiops truncatus) interaction with fish farms in the Gulf of Ambracia, western Greece

Abstract

Abstract Marine aquaculture, and its fast‐growing development, has the potential for wider environmental, ecosystem, and biodiversity impacts. This study assesses the impact of fish farming on a bottlenose dolphin (Tursiops truncatus) population within the Gulf of Ambracia (western Greece) between 2007 and 2018. Two different study areas were defined in order to investigate differences on occurrence, abundance, behaviour, and seasonal fluctuations between them: a ‘control area’, in the north‐western side of the Gulf; and a ‘fish farm area’, in the south west, where the highest density of fish farm cages is found. A total of 169 daily surveys were dedicated to the control area and 74 days were dedicated to the fish farm area, yielding 104 and 37 sightings, respectively. Both the probability of detecting dolphins (U = 6,763.000, P = 0.002) and the group sizes (U = 578.000, P < 0.001) were smaller around fish farms. Seasonality analyses were restricted to 2007–2008, as this was the period with year‐round effort. Results revealed that dolphins were more frequently seen around fish farms in the winter (Kruskal–Wallis test, P = 0.036). From the 40 identified individuals that were re‐sighted at least 10 times during the study period, 21 used the fish farm area less than expected according to sampling effort, and 10 of them were never observed in that area (binomial test, P < 0.05). The results revealed an impact of fish farms on the distribution of bottlenose dolphins in the Gulf of Ambracia. This information should be taken into consideration when defining ecosystem‐based management measures within the management plan, which is currently in preparation for this Natura 2000 site.