Assessment of Harbour Porpoise Bycatch along the Portuguese and Galician Coast: Insights from Strandings over Two Decades

Abstract

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.

Microplastics in Cetaceans Stranded on the Portuguese Coast

“…Considering the existing threats affecting cetacean populations (e.g., by-catch, anthropogenic noise, hunting) [43], it is important to understand whether microplastic pollution poses an additional risk to these populations [41]. The assessment of additional risks is particularly needed on the Atlantic Iberian coast, given the important cetacean bycatch mortality in the area, especially in the case of the critically endangered Iberian porpoise (Phocoena phocoena) population [44,45]. To obtain results on plastic litter affecting cetaceans, it has been recommended that national marine mammal stranding networks play an active role in the collection of samples for marine litter analyses and increase the studies on the impacts of marine plastic pollution on cetaceans [41,46,47].…”

Harbor porpoise losing its edge: Genetic time series suggests a rapid population decline in Iberian waters over the last 30 years

“…Furthermore, Iberian harbor porpoises are regularly found stranded, often with signs of bycatch mortality, potentially indicating unsustainable mortality rates (IMR‐NAMMCO, 2019 ; López et al., 2002 ; Pierce et al., 2020 ; Read et al., 2020 ; Torres‐Pereira et al., 2022 ; Torres‐Pereira, Araújo, et al., 2023 ; Vingada & Eira, 2018 ). In fact, based on Portuguese stranding data, an average of 9.19% (CI = 5.25%–16.10%) of the porpoise population was estimated to be removed annually by fisheries between 2011 and 2015, corresponding to an average of 207 porpoises removed per year, which largely surpasses the Potential Biological Removal rate conservatively estimated for the same period (22 porpoises, CI: 12–43) (Torres‐Pereira, Araújo, et al., 2023 ). An additional cause for concern is related to the potential overexploitation of the feeding resources (Méndez‐Fernandez et al., 2013 ; Santos & Pierce, 2003 ).…”