Interactions between small cetaceans and the\ud purse-seine fishery in western Portuguese waters

Marine mammal interactions with Portuguese purse-seine fisheries operating in four different ports (Figueira\ud da Foz, Sesimbra, Setúbal, Sines) were studied (July-October 2003). Observers accompanied commercial fishing vessels and\ud monitored 48 fishing trips. An interview survey of skippers was also carried out (n = 36). Three species of marine mammals\ud were observed in 31 sightings during the commercials trips but only the species Delphinus delphis and the category\ud Delphinidae were observed to interact with fishing activities. Small cetaceans were observed to sink, gather or disperse\ud school fishes and damage gear. Mean CPUE and fishing effort values did not change significantly in the presence of dolphins\ud (H = 0.06 and H = 0, both p>0.05). Results from Figueira da Foz indicate that cetaceans are attracted to fishing grounds\ud with a high abundance of their prey-species. Fishermen reported three by-catch events off Figueira da Foz. Compared with\ud other fisheries, purse-seine fishing does not seem to be among the most damaging to marine mammals