INTERACÇÕES DA PESCA DE CERCO COM POPULAÇÕES DE PEQUENOS CETÁCEOS NA COSTA PORTUGUESA

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Assessment of harbour porpoise bycatch along the Portuguese and Galician Coast: insights from strandings over two decades

Publication . Torres-Pereira, Andreia; Araújo, Hélder; Monteiro, Silvia Silva; Ferreira, Marisa; Bastos-Santos, Jorge; Sá, Sara; Nicolau, Lídia; Marçalo, Ana; Marques, Carina; Tavares, Ana Sofia; De Bonis, Myriam; Covelo, Pablo; Martínez-Cedeira, José; López, Alfredo; Sequeira, Marina; Vingada, José; Eira, Catarina

The Iberian harbour porpoise population is small and fisheries bycatch has been described as one of its most important threats. Data on harbour porpoise strandings collected by the Portuguese and Galician stranding networks between 2000 and 2020 are indicative of a recent mortality increase in the western Iberian coast (particularly in northern Portugal). Overall, in Portugal and Galicia, individuals stranded due to confirmed fishery interaction represented 46.98% of all analysed porpoises, and individuals stranded due to probable fishery interaction represented another 10.99% of all analysed porpoises. Considering the Portuguese annual abundance estimates available between 2011 and 2015, it was possible to calculate that an annual average of 207 individuals was removed from the population in Portuguese waters alone, which largely surpasses the potential biological removal (PBR) estimates (22 porpoises, CI: 12–43) for the same period. These results are conservative and bycatch values from strandings are likely underestimated. A structured action plan accounting for new activities at sea is needed to limit the Iberian porpoise population decline. Meanwhile, there is an urgent need for a fishing effort reorganization to directly decrease porpoise mortality.

2023-08-15Journal article

Open Access

Interactions between the common dolphin, Delphinus delphis, and the Portuguese purse seine fishery over a period of 15 years (2003–2018)

Publication . Dias, Inês C.; Marçalo, Ana; Feijó, Diana; Domingos, Isabel; Silva, Alexandra A.

Interactions between cetaceans and the purse seine fishery in coastal waters of mainland Portugal were investigated using onboard observations over a period of 15 years (2003-2018). In 10% of the fishing sets, there were interactions with one of three species of cetaceans: common dolphin (Delphinus delphis), bottlenose dolphin (Tursiops truncatus), and harbour porpoise (Phocoena phocoena). The common dolphin was the most frequently observed species, occurring in 89% of all interaction events, and the only species with observed mortality. Therefore, this study focused only on the interactions with common dolphins. A generalized additive model (GAM) was applied to observer data to investigate how the fishing activity and the abundance of small pelagic fish influenced the probability of occurrence of interactions between the common dolphin and the purse seine fishery between 2003 and 2018. The results revealed significant annual and geographic variation in the occurrence of interactions, and a significant influence of fishing effort and catch per unit effort of sardine (Sardina pilchardus). A second GAM in a hurdle model was used to model the number of common dolphins that interacted with the fishing activity as a function of fishing seasonality and the local abundance of pelagic fish. There was a significant effect of the seasonality of the fishing activity and catch per unit effort of sardine and chub mackerel (Scomber colias) on the number of common dolphins interacting with the fishery. The results of this study suggest that the probability of interactions and the number of common dolphins interacting with the fishery were affected by the local abundance of sardine and chub mackerel. As the common dolphin population appears to be increasing in the study area, the risk of by-catch also increases, thus the monitoring of the Portuguese purse seine fishery is important to inform the implementation of management plans, and also as a response to global efforts for sustainable fisheries and marine mammal conservation.

2022Journal article

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Portuguese purse seine fishery spatial and resource overlap with top predators

Publication . Wise, Laura; Galego, Catarina; Katara, Isidora; Marçalo, Ana; Meirinho, Ana; Monteiro, Silvia S.; Oliveira, Nuno; Santos, Jorge; Rodrigues, Pedro; Araujo, Helder; Vingada, Jose; Silva, Alexandra

The Portuguese purse seine fishery, with average annual catches of 70 000 tonnes, operates mainly in coastal areas and targets small pelagic fish (SPF). Potential competition for resources may occur between the fishery and some species of marine mammals and seabirds, as suggested by observed incidental catches. For those species directly affected by the fishery, the spatial distribution of marine taxa and the fishing fleet are key pieces of information for spatial planning and management. We analysed the spatial and resource overlap between the fishery's distribution and effort, and the distribution and abundance of 6 species of top predators -seabirds (n = 4) and marine mammals (n = 2) between 2010 and 2014. Estimates of annual consumption by top predators and the fishery catch within the distributional range of one of their main prey species (sardine Sardina pilchardus) were also determined. Spatial overlap between all considered species and the fishery was low (<0.221), and only 2 species (common dolphins Delphinus delphis and Cory's shearwaters Calonectris borealis) showed high resource overlap with the fishery (>0.7). Overall, values of consumption of SPF by the top predators were of the same order of magnitude as mean annual purse seine landings for the studied area. Our results can be used for marine spatial planning, including designation of Marine Protected Areas and the development of an ecosystem-based model for the effective management of the Portuguese purse seine fishery that takes into account the consumption of natural predators.

2019-05Journal article

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