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Abstract
Marine mammal interactions with Portuguese purse-seine fisheries operating in four different ports (Figueira da Foz, Sesimbra, Setubal, Sines) were studied (July-October 2003). Observers accompanied commercial fishing vessels and monitored 48 fishing trips. An interview survey of skippers was also carried out (n = 36). Three species of marine mammals were observed in 31 sightings during the commercials trips but only the species Delphinus delphis and the category Delphinidae were observed to interact with fishing activities. Small cetaceans were observed to sink, gather or disperse school fishes and damage gear. Mean CPUE and fishing effort values did not change significantly in the presence of dolphins (H = 0.06 and H = 0, both p>0.05). Results from Figueira da Foz indicate that cetaceans are attracted to fishing grounds with a high abundance of their prey-species. Fishermen reported three by-catch events off Figueira da Foz. Compared with other fisheries, purse-seine fishing does not seem to be among the most damaging to marine mammals.
Highlights
Many fisheries around the world have significant interactions with marine mammals (Northridge, 1991; STECF, 2002)
SUMMARY: Marine mammal interactions with Portuguese purse-seine fisheries operating in four different ports (Figueira da Foz, Sesimbra, Setúbal, Sines) were studied (July-October 2003)
Three species of marine mammals were observed in 31 sightings during the commercials trips but only the species Delphinus delphis and the category Delphinidae were observed to interact with fishing activities
Summary
Many fisheries around the world have significant interactions with marine mammals (Northridge, 1991; STECF, 2002). In Portuguese continental waters, data on stranding records and fishermen’s reports indicate that incidental capture of small cetaceans and other operational interactions take place mainly in gillnet fisheries (Sequeira et al, 1997; STECF, 2002) Fisheries such as purse-seining for small pelagics (Parente, 2000; Stratoudakis and Marçalo, 2002) provide an opportunity for operational interactions with small cetaceans for two main reasons: (i) purse-seiners target the main prey species of small cetaceans (Northridge, 1991; Pauly et al, 1998; Silva, 1999; Santos et al, 2004; Santos et al, 2007) and (ii) they operate within their distribution area (Sequeira and Ferreira, 1994; Silva and Sequeira, 2003). Purse-seiners operate mainly from sunset to sunrise, coinciding with the feeding period of dolphins (Waring et al, 1990; Aguilar, 1997; Crespo et al, 1997) and increasing the potential for cetacean-fisheries interactions
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