Ecological value of top predators and the case study of blue shark

• Autor(a) principal: Silva, Inês Machado Bota da
• Data de Publicação: 2021
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/30813
• topic: Top predator; Fishing; Prionace glauca; Landings; Portugal

Top predators have an important role in the trophic chain, especially in marine ecosystems, where the hypothesis that pristine biomass pyramids are inverted and therefore, with a more pronounced top-down control, is highly debated. Their abundance, however, have showed a marked decline over the years, due to exploitation and human-predator conflicts. Currently, a better appreciation of the importance of the relationships between species, have pushed areas like fishery research, to look at ecosystem-based management, with multispecies management strategies. Sharks are notorious predators, highly vulnerable to the many threats they face, due to their biological characteristics. Particularly, blue shark (Prionace glauca), because of its wide distribution is one of the shark species most impacted by fisheries. Here, the objective is to understand what can be inferred about the state of the blue shark population using records of landings in Portuguese ports, since 1989. The analysis focused on data of landings, average price, and size. Results showed a tendency for decreasing landings and increasing average price over time, which can be associated with overfishing. Size data was very inconstant and not very informative, it did not seem as relevant for juvenile protection as it could and should be. General measures for blue shark protection have been implemented since 2016, but more attention should be given to the large number of juveniles that inhabit the Exclusive Economic Zone (EEZ) of Portugal. Further studies could focus on the ecological value of this species for the ecosystem and, particularly in Portugal, on a better understanding of the market and of consumer knowledge and awareness.