Interactions between bottlenose dolphins (Tursiops truncatus) and fishing activites in the northern adriatic sea

Interactions between cetaceans (Cetacea) and fisheries are a widespread occurrence in the Mediterranean Sea and worldwide, effects of which range from positive to negative for one or both sides involved. We studied interactions between common bottlenose dolphins (Tursiops truncatus) and different types of trawlers in the Gulf of Trieste and adjacent waters, as part of a long-term study on bottlenose dolphin ecology and conservation. We carried out visual boat- and land-based surveys between 2002 and 2012. During boat suveys, we opportunistically inspected operating trawlers for dolphin presence. When encountered, with or without trawlers, dolphins were followed for a variable amount of time, and photographed for identification purposes. Out of 205 recorded sightings, 22 % involved an interaction with trawlers. 51,1 % of those interactions were with pelagic pair trawlers, while 46,7 % were with (single) bottom trawlers. Even though the frequency of interactions among two types of trawlers was similar, dolphins appeared more likely to follow pelagic pair trawlers, with the fleet size 15 times smaller than that of bottom trawlers. Group size during interactions ranged from 1 to 28 individuals. Calves were present in almost half of all interactions. The animals followed trawlers for a variable amount of time, from 9 to 149 minutes. Photo-identification data showed that most recorded interactions involved the same identified individuals, while such behaviour was never observed in others. We also compared the frequency of interactions with trawler catch quantity and type. Both types of trawlers appear to attract dolphins and thus alter their movements and behaviour