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Regional and temporal patterns of bycatch landings in the purse seine fishery
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Resumo(s)
Purse seine fishing is one of the main fishing methods used in Portugal and targets mainly sardine (Sardina pilchardus). Although considered selective for small pelagic fish, a wide range of bycatch species subject to catch limitations, occur in the landings. The value and volume of bycatch are not well understood, making it difficult to assess its ecological impact and regional and temporal trends in catches. This study analysed purse seine fishing landings in mainland Portugal between 2000 and 2022, using data provided by the Portuguese Fisheries Directorate. The data were reorganised and processed in R, with new variables created (type of vessel, date, average price per kilogramme and region). The coast was divided into four regions – North, Centre, Southwest and South – based on their physical, ecological and socio-economic differences. An initial filtering process was performed to select the species representing 90% of the total landings by value, with four small pelagic fish considered target species by legislation standing out: sardine, chub mackerel (Scomber colias), European anchovy (Engraulis encrasicolus) and horse mackerel (Trachurus trachurus). A second phase identified eight more species that were relevant at the regional level. Spatial and temporal trends of landings were analysed using an R application adapted to our data, revealing sales peaks in the summer and consistent quantities by species over the years. The Centre was identified as the most important region in terms of both weight and value of landings, whereas the South contributed less. A LOESS analysis using inflation-adjusted values showed that the real income received in 2022 was similar to or lower than that received in 2000, indicating a decline in the purchasing power of fishermen, despite rising nominal prices. Cross-correlation analyses revealed positive temporal relationships between species, which were more complex in the South. The results also highlighted discrepancies between the importance of certain species and their classification as target or bycatch on the legislation, especially at the regional level, underscoring the need for a legislation reform.
Descrição
Relatório de Estágio de Mestrado, Ecologia e Gestão Ambiental, 2026, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Target species Trend Regulation Mitigation measures