Browsing by Author "Cabral, Henrique N."
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- Environmental influence on commercial fishery landings of small pelagic fish in PortugalPublication . Teixeira, Célia M.; Gamito, Rita; Miguel de Sousa Leitão, Francisco; Murta, Alberto G.; Cabral, Henrique N.; Erzini, Karim; Costa, Maria JoséSmall pelagic fishes are particularly abundant in areas with high environmental variability (zones of coastal upwelling and areas of tidal mixing and river discharge), and because of this, their abundance suffers large inter-annual and inter-decadal fluctuations. In Portugal, the most important species in terms of landings are European sardine, Atlantic horse mackerel and Atlantic chub mackerel. Small pelagic fish landings account for 62.8 % of the total fish biomass and represent 32.7 % of the economical value of all catches. We have investigated trends in landings of these small pelagic fishes and detected the effects of environmental factors in this fishery. In order to explain the variability of landings of small pelagic fishes, we have used official landings (1965-2012) for trawling and purse seine fisheries and applied generalized linear models, using the North Atlantic Oscillation index (NAO) (annual and winter NAO index), sea surface temperature (SST), wind data (strength and North-South and East-West wind components) and rainfall, as explanatory variables. Regression analysis was used to describe the relationship between landings and SST. The models explained between 50.16 and 51.07 % of the variability of the LPUE, with the most important factors being winter NAO index, SST and wind strength. The LPUE of European sardine and Atlantic horse mackerel was negatively correlated with SST, and LPUE of Atlantic chub mackerel was positively correlated with SST. The use of landings of three important species of small pelagic fishes allowed the detection of variations in landings associated with changes in sea water temperature and NAO index.
- Fishers' behaviour in response to the implementation of a marine protected areaPublication . Horta e Costa, Bárbara; Gonçalves, Leonel; Erzini, Karim; Caselle, Jennifer E.; Cabral, Henrique N.; Gonçalves, Emanuel J.Marine Protected Areas (MPAs) have been widely proposed as a fisheries management tool in addition to their conservation purposes. Despite this, few studies have satisfactorily assessed the dynamics of fishers' adaptations to the loss of fishing grounds. Here we used data from before, during and after the implementation of the management plan of a temperate Atlantic multiple-use MPA to examine the factors affecting the spatial and temporal distribution of different gears used by the artisanal fishing fleet. The position of vessels and gear types were obtained by visual surveys and related to spatial features of the marine park. A hotspot analysis was conducted to identify heavily utilized patches for each fishing gear and time period. The contribution of individual vessels to each significant cluster was assessed to better understand fishers' choices. Different fisheries responded differently to the implementation of protection measures, with preferred habitats of target species driving much of the fishers' choices. Within each fishery, individual fishers showed distinct strategies with some operating in a broader area whereas others kept preferred territories. Our findings are based on reliable methods that can easily be applied in coastal multipurpose MPAs to monitor and assess fisheries and fishers responses to different management rules and protection levels. This paper is the first in-depth empirical study where fishers' choices from artisanal fisheries were analysed before, during and after the implementation of a MPA, thereby allowing a clearer understanding of the dynamics of local fisheries and providing significant lessons for marine conservation and management of coastal systems.
- Padrões de distribuição de associações de macroinvertebrados bentónicos em pequenos estuários da costa Portuguesa - terão utillidade na gestão costeira?Publication . Cardoso, Inês; Cabral, Henrique N.; Cancela Da Fonseca, LuísAs comunidades de macroinvertebrados bentónicos são altamente variáveis, mesmo em pequenas escalas espaciais, mas desempenham um papel fundamental em ambientes estuarino-lagunares na: i) sua elevada produtividade; ii) implementação de planos de monitorização; iii) aplicação de ferramentas de avaliação da qualidade ecológica. A compreensão dos respectivos padrões de distribuição é relevante para diferenciar a variabilidade natural, dos padrões induzidos por impactos antrópicos. Estas comunidades foram estudadas em cinco pequenos estuários do sul e sudoeste português, para perceber, entre e dentro dos sistemas, a influência de características ambientais na respectiva estrutura. O conhecimento dos padrões de distribuição em cada sistema é determinante para: i) quantificar factores concretos de impacto; ii) mitigar o risco de perda do seu valor ecológico e funcional; iii) futuras comparações entre sistemas, iv) quantificar a sua vulnerabilidade. Os cinco sistemas mostraram composições distintas das comunidades bentónicas, com a dominância de espécies diferentes entre eles. Numa escala mais ampla (entre sistemas), os componentes dos sedimentos explicam as principais diferenças nessas comunidades. Dentro dos sistemas, os padrões não podem ser atribuídos à heterogeneidade dos sedimentos. Além disso, a sazonalidade, um proxy da salinidade, não teve o mesmo impacto em sistemas equivalentes, subjacente à complexidade de fatores que podem atuar em pequenas escalas em sistemas de reduzidas dimensões. Para fins de monitorização, concluiu-se que a análise da comunidade não deve descartar a composição especifica, pois esta pode fornecer informações fundamentais sobre as características do sistema quando os dados disponíveis são escassos.Concluiu-se igualmente neste contexto, que: i) os procedimentos de amostragem devem cobrir não só a heterogeneidade do sistema (não apenas por amostragem ao longo de gradientes estuarinos), mas também abarcar a variação sazonal que pode ser de grande importância para alguns pequenos estuários; ii). as associações de macroinvertebrados bentónicos, usualmente consideradas como bons indicadores do estado ambiental em sistemas estuarinos, só terão utilidade na gestão costeira se combinados com outros indicadores relativos às actividades antrópicas, avaliando os respectivos impactos. Toda esta informação poderá interessar autoridades e “stakeholders” em termos de gestão e conservação.
- Trends in landings of fish species potentially affected by climate change in Portuguese fisheriesPublication . Teixeira, Célia M.; Gamito, Rita; Leitão, Francisco; Erzini, Karim; Costa, Maria J.; Cabral, Henrique N.Fisheries are an important source of food, with a high economic value and social significance. The present worrying situation of the world fisheries is the result of the interaction between different factors (e.g. climatic variations, natural oscillations, technological innovation), but the greatest challenges are overfishing and climate change. The species richness of the Portuguese coast is generally higher than that found in northern Europe and similar to that of the Mediterranean, since many species have their southern or northern distribution limits along the Portuguese coast. The zoogeographic importance of this latitudinal area has long been recognized, representing the transition between north-eastern Atlantic warm-temperate and cold-temperate regions, which makes the Portuguese coast an area of great sensitivity to the detection of climate change. Official landing data for commercial species that have the Portuguese coast as their distribution limit were analysed together with sea surface temperature for the period of 1927-2011. In general, landings of species with affinity for temperate waters presented a decreasing trend, whereas species with affinity for subtropical/tropical waters showed an increasing trend. These variations were associated with variation in temperature: lower landings of temperate species occurred mainly in warm years, whereas landings of subtropical/tropical species presented an opposite trend, with higher landings in warm years. Preparing for the impacts of climate change is crucial for the sustainability of fisheries. Management should take into consideration information about environmental factors that affect species distribution and abundance.