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Publication
Distribuição espácio-temporal da Enguia-europeia na Ilha da Madeira
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Authors
Advisor(s)
Abstract(s)
A enguia-europeia (Anguilla anguilla), uma espécie globalmente ameaçada, enfrenta
um declínio populacional significativo. A Ilha da Madeira possui ecossistemas de água doce
adequados para sustentar a subpopulação de enguias. Contudo, as suas necessidades ecológicas
e de conservação permanecem pouco explorados na região. Com o intuito de identificar padrões
sazonais específicos na região, este estudo investigou a relação entre a distribuição espáciotemporal da enguia-europeia e fatores ambientais (temperatura) e geográficos (altitude,
distância ao mar e número de potenciais barreiras à colonização). Para tal, as enguias foram
capturadas com o método de pesca elétrica em três troços de seis ribeiras da Ilha, durante dois
anos e em três épocas anuais. Modelos lineares e lineares generalizados mistos foram utilizados
para testar a correlação entre densidade populacional, tamanho corporal, estágio de vida e sexo
das enguias e os fatores ambientais e geográficos. Esperava-se observar uma diminuição da
densidade de enguias e um aumento no número de enguias de maior tamanho ao longo das
ribeiras no sentido montante. Era também esperado que a distribuição espacial fosse distinta
entre machos e fêmeas, e entre enguias em diferentes fases de vida em função da época do ano.
Observou-se uma maior abundância de enguias a jusante, negativamente correlacionado com
os açudes e a distância ao mar. Além disso, observou-se um padrão sazonal mais evidente para
as fêmeas migratórias- mais abundantes em troços a montante no outono. Estes resultados
contribuem para a compreensão da distribuição sazonal das enguias em ilhas oceânicas,
relevantes no planeamento de estratégias de conservação eficazes.
ABSTRACT: The European eel (Anguilla anguilla), a globally threatened species, faces significant population decline. Madeira Island has freshwater ecosystems suitable to support the eel subpopulation. However, its ecological and conservation needs remain poorly explored in the region. To identify specific seasonal patterns in the region, this study investigated the relationship between the spatio-temporal distribution of the European eel and environmental (temperature) and geographic factors (altitude, distance from the sea and number of potential barriers to colonization). To this end, the eels were captured using the electrofishing method in three sections of six streams on the Island, for two years and in three annual seasons. Linear and generalised linear mixed models were used to test the correlation between population density, body size, life stage and sex of the eels and environmental and geographic factors. It was expected to observe a decrease in eel density and an increase in the number of larger eels along the upstream streams. It was also expected that the spatial distribution would be different between males and females, and between eels at different life stages depending on the season. Greater abundance of eels was observed downstream, negatively correlated with weirs and distance from the sea. Furthermore, a more evident seasonal pattern was observed for migratory females - more abundant in upstream reaches in autumn. These results contribute to the understanding of the seasonal distribution of eels on oceanic islands, relevant for planning effective conservation strategies.
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ABSTRACT: The European eel (Anguilla anguilla), a globally threatened species, faces significant population decline. Madeira Island has freshwater ecosystems suitable to support the eel subpopulation. However, its ecological and conservation needs remain poorly explored in the region. To identify specific seasonal patterns in the region, this study investigated the relationship between the spatio-temporal distribution of the European eel and environmental (temperature) and geographic factors (altitude, distance from the sea and number of potential barriers to colonization). To this end, the eels were captured using the electrofishing method in three sections of six streams on the Island, for two years and in three annual seasons. Linear and generalised linear mixed models were used to test the correlation between population density, body size, life stage and sex of the eels and environmental and geographic factors. It was expected to observe a decrease in eel density and an increase in the number of larger eels along the upstream streams. It was also expected that the spatial distribution would be different between males and females, and between eels at different life stages depending on the season. Greater abundance of eels was observed downstream, negatively correlated with weirs and distance from the sea. Furthermore, a more evident seasonal pattern was observed for migratory females - more abundant in upstream reaches in autumn. These results contribute to the understanding of the seasonal distribution of eels on oceanic islands, relevant for planning effective conservation strategies.
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Description
Dissertação de Mestrado apresentada no Ispa – Instituto
Universitário para obtenção de grau de
Mestre na especialidade de Biologia
Marinha e Conservação
Keywords
Anguilla anguilla Colonização Ecossistemas de água doce Variações espácio-temporais Variáveis de macroescala Anguilla anguilla Colonization Freshwater ecosystemS Spatiotemporal variations Geographic variables