Publicação
Assessment of discards in the purse-seine fishery along the Portuguese coast
| Resumo: | Discards, the portion of the catch returned to the sea, represent a loss of resources as well as a potential ecological concern. This study aimed to characterise and evaluate discards in the purse-seine fishery, a key component of Portuguese fisheries targeting small pelagic species. Data were collected by onboard observers between 2006 and 2019. The species composition of four catch fractions, landings, discards, slipping and crew consumption were examined, and three discard importance indices were developed. Preliminary values of fleet-level discards were obtained with Cochran landing-to-ratio estimator. While overall discard rates were low, reflecting the high selectivity of the Portuguese purse-seine fishery, species and zone-specific peaks indicated occasional shifts in fishing practices or management constraints. The species most frequently discarded included chub mackerel, bogue and Atlantic horse mackerel. Spatial analysis revealed that discards in the North were dominated by sardine and European anchovy, while bogue and chub mackerel were most prevalent in the Center, Southwest, and South. Chub mackerel emerged as the most significant species across all importance indices. Discard patterns varied between species and fishing zones, showing no clear relationship with quotas, median length, or average market price. Despite this, a significant positive correlation was found between median length and discarded weight for species like horse mackerel and chub mackerel, suggesting larger specimens were discarded when vessel capacity is reached. Economically, sardines showed higher discards during periods of higher prices and lower quotas, suggesting that regulatory constraints significantly influenced discarding behaviour. Discard estimates showed high coefficients of variation (CV > 40%) and therefore should be interpreted with caution. Our results suggested that discard patterns are likely shaped by a combination of factors. Understanding these patterns is essential for the development of targeted management and mitigation measures to ensure the sustainable exploitation of small pelagic resources along the Portuguese coast. |
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| Autores principais: | Piecho,Rita Pires |
| Assunto: | Fisheries sustainability mitigation measures resource management catch composition fishing regulations |
| Ano: | 2026 |
| País: | Portugal |
| Tipo de documento: | dissertação de mestrado |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | Discards, the portion of the catch returned to the sea, represent a loss of resources as well as a potential ecological concern. This study aimed to characterise and evaluate discards in the purse-seine fishery, a key component of Portuguese fisheries targeting small pelagic species. Data were collected by onboard observers between 2006 and 2019. The species composition of four catch fractions, landings, discards, slipping and crew consumption were examined, and three discard importance indices were developed. Preliminary values of fleet-level discards were obtained with Cochran landing-to-ratio estimator. While overall discard rates were low, reflecting the high selectivity of the Portuguese purse-seine fishery, species and zone-specific peaks indicated occasional shifts in fishing practices or management constraints. The species most frequently discarded included chub mackerel, bogue and Atlantic horse mackerel. Spatial analysis revealed that discards in the North were dominated by sardine and European anchovy, while bogue and chub mackerel were most prevalent in the Center, Southwest, and South. Chub mackerel emerged as the most significant species across all importance indices. Discard patterns varied between species and fishing zones, showing no clear relationship with quotas, median length, or average market price. Despite this, a significant positive correlation was found between median length and discarded weight for species like horse mackerel and chub mackerel, suggesting larger specimens were discarded when vessel capacity is reached. Economically, sardines showed higher discards during periods of higher prices and lower quotas, suggesting that regulatory constraints significantly influenced discarding behaviour. Discard estimates showed high coefficients of variation (CV > 40%) and therefore should be interpreted with caution. Our results suggested that discard patterns are likely shaped by a combination of factors. Understanding these patterns is essential for the development of targeted management and mitigation measures to ensure the sustainable exploitation of small pelagic resources along the Portuguese coast. |
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