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

Interakcije med kiti in delfini (Cetacea) ter ribištvom so zelo pogost pojav tako v Sredozemskem morju, kot tudi drugod po svetu. Posledice interakcij so lahko pozitivne ali negativne za eno ali obe strani. V sklopu dolgoletne raziskave ekologije in varstva velike pliskavke (Tursiops truncatus) v Tržaškem zalivu in okoliških vodah smo proučevali interakcije med veliko pliskavko in različnimi tipi povlečnih ribiških mrež (t.i. »koče«). Opazovanja smo izvajali s plovil in kopenskih opazovalnih točk, med leti 2002 in 2012. Med iskanjem delfinov smo priložnostno pregledovali aktivne koče in ugotavljali morebitno prisotnost delfinov za njimi. Ob vsakem opažanju smo delfine fotografirali za individualno identifikacijo. Izmed skupno 205 opažanj smo v 22 % zabeležili interakcije delfinov s kočami, od katerih je bilo 51,1 % interakcij s pelagično vlečno mrežo, upravljano z dveh plovil (»pelagična koča«). Preostalih 46,7 % interakcij je bilo s pridnenimi vlečnimi mrežami s širilkami (»pridnene koče«). Čeprav je bil odstotek interakcij med obema tipoma ribolovnega orodja podoben, so delfini nekoliko pogosteje sledili pelagičnim kočam, ki jih je bilo številčno kar 15-krat manj kot pridnenih koč. Velikost skupin delfinov, ki so sledili kočam, se je gibala med 1 in 28 osebkov. Prisotnost mladičev je bila zabeležena v skoraj polovici vseh interakcij. Zabeležen čas trajanja interakcij se je gibal med 9 in 149 minut. S pomočjo fotoidentifikacije posameznih osebkov smo ugotovili, da so v večini interakcij sodelovali isti osebki, medtem, ko pri drugih osebkih tega vedenja ni bilo zaslediti. Primerjali smo tudi količino in tip ulova rib s pogostostjo interakcij. Rezultati kažejo, da koče privabljajo nekatere delfine in tako vplivajo na njihovo gibanje in vedenje.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