Human-induced cetacean mortality in the Adriatic sea

Human influence on cetacean mortality is evident in many regions. Some humancetacean interactions which result in high cetacean mortality, like by catch, can even impact the population dynamics of small or localized cetacean populations. The Adriatic Sea is inhabited by only one resident cetacean species - the bottlenose dolphin. There are no data on the population size, but it is estimated that there are around 250 bottlenose dolphins in the Croatian part of the Adriatic Sea. We studied the incidence and nature of human induced mortality of cetaceans stranded in the Croatian part of the Adriatic Sea from October 1990 till November 2008. Postmortem examinations were performed on 158 cetacean carcasses consisting of 127 bottlenose dolphins (Tursiops truncatus), 18 striped dolphins (Stenella coeruleoalba), seven Risso's dolphins (Grampus griseus), four Cuvier's beaked whales (Ziphius cavirostris) and two fin whales (Balaenoptera physalus) ; while the cause of death was determined in 57.6% of cases. Human induced mortality was higher in the resident bottlenose dolphins (62.3% animals) than in the non-resident cetaceans (27.3% animals). In bottlenose dolphins, by-catch was the most prevailing human induced cause of death (22 animals), followed by larynx strangulation with gillnet parts (12 animals), gun wounds (4 animals), physical traumatic injuries (3 animals) and presumed blast trauma caused by dynamite fishing (2 animals). Human induced mortality in the non-resident cetaceans was represented by bycatch (4 animals) and physical traumatic injuries (2 animals). Conservation measures likely to mitigate the problem of human induced cetacean mortalities remain to be identified and implemented.