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Assessment of harbour porpoise bycatch along the Portuguese and Galician coast: insights from strandings over two decades
Andreia Torres-Pereira, H?lder Ara?jo, Jorge Bastos-Santos, Sara S?, L?dia Nicolau, Ana Mar?alo, Carina Marques, Marisa Ferreira, Pablo Covelo, Jos? Mart?nez-Cedeira, Alfredo L?pez, Marina Sequeira, Jos? Vingada, Catarina Eira
The harbour porpoise population in the Iberian Peninsula is small and fisheries bycatch has been described as one its most important threats. Considering the many difficulties in bycatch monitoring methods, marine mammal stranding networks may provide important information on populations and individual cause of death. Information on harbour porpoise strandings collected by the strandings networks in Portugal and in Galicia indicates that most strandings occurred in the central coast of Portugal (North sector) and in the southern Rias Baixas in Galicia (Spain), showing an apparent recent increase (particularly in northern Portugal). Overall, in Portugal and Galicia, individuals stranded due to confirmed bycatch represented 46.98% of all analysed porpoises, and individuals stranded due to probable bycatch represented another 10.99% of all analysed porpoises. However, no cause of death was determined for a quarter of the analysed porpoises. Considering the period between 2011 and 2015 (available population annual abundance estimates) our overall PBR estimates indicate an ?acceptable? average annual removal of 22 porpoises (CI: 12-43) in Portuguese waters alone. However, we estimated that an annual average of 125 individuals was removed from the population during that period, in Portugal. The annual population removal estimate is conservative and bycatch values from strandings are surely underestimated. If we aim at halting the porpoise decline in Portugal and Spain, at least a strict implementation of EU directives and fisheries legislation is crucial as well as a structured action plan directed at the conservation of the Iberian Porpoise. Meanwhile, there is an urgent need for a decrease in fishing effort to decrease porpoise mortality.