Publicação
Small pelagics, predatory fish and seabirds : trophic and behavioural interactions in a marine protected area in Guinea-Bissau
| Resumo: | Rapid and significant declines in marine biodiversity, caused by overfishing and global changes, are affecting the functioning of marine ecosystems worldwide. Understanding food-web dynamics is essential for the development of efficient ecosystem management actions. In West Africa, knowledge of food-web dynamics is particularly urgent given that fish stocks are collapsing and fisheries sustain the livelihoods of a significant part of the human population. This thesis addresses the trophic interactions of the marine community of the Bijagós Archipelago, Guinea-Bissau. The extensive mangroves and mudflats of this continental archipelago make it an important area for several migratory species (e.g. marine turtles, waders) and resident species (e.g. seabirds), as well as a nursery area for several fish species. The great biodiversity value of the Bijagós led it to be declared as UNESCO Biosphere Reserve in 1996 and a Ramsar site in 2014. Nevertheless, few studies have been conducted in its marine ecosystem. Seasonal, lunar tidal and diel variations of the coastal small fish community of the Bijagós Archipelago were studied through beach seining along spatial and temporal scales. The diet and foraging behaviour of marine predators (predatory fishes and seabirds) was also studied, with particular interest in their facilitative feeding associations. Traditional methods were used for diet description, such as, the macroscopic identification of prey remains from stomach contents of predatory fish and pellets of breeding seabirds. We also used next-generation sequencing, employing DNA metabarcoding on the identification of prey in the droppings of wintering seabirds. This was the first time this method was used for studying the feeding ecology on migratory birds in their wintering quarters. Additionally, behavioural focal observations of seabirds were performed to investigate their feeding habits. Given the lack of previous descriptive studies, this work also focuses the particularities of length-weight relationships of six fish species. The present study showed that the marine ecosystem of the Bijagós is strongly dominated by a small pelagic fish species, Sardinella maderensis. This species was the most abundant throughout the year as well as in all the islands, and the most frequent item in the diet of all marine predators. In regards to facilitative foraging, different species of seabirds showed distinctive degrees of reliance on associations, ranging from completely independent to near-obligatory. The results also suggest that the use of associations influences the distribution of seabird species and may enhance their foraging success. The overall findings presented here indicate that the marine ecosystem of the Bijagós Archipelago is a wasp-waist type, with Sardinella maderensis as the key small pelagic species, and that an ecosystem-based approach must be considered for the adequate management of the archipelago. Declines in populations of predatory fish and small pelagic fish are both likely to influence the distribution and foraging success of seabirds, with impacts on their survival and breeding success. |
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| Autores principais: | Correia, Edna Rita de Freitas da Costa |
| Assunto: | Teses de doutoramento - 2018 |
| Ano: | 2018 |
| País: | Portugal |
| Tipo de documento: | tese de doutoramento |
| Tipo de acesso: | acesso aberto |
| Instituição associada: | Universidade de Lisboa |
| Idioma: | inglês |
| Origem: | Repositório da Universidade de Lisboa |
| Resumo: | Rapid and significant declines in marine biodiversity, caused by overfishing and global changes, are affecting the functioning of marine ecosystems worldwide. Understanding food-web dynamics is essential for the development of efficient ecosystem management actions. In West Africa, knowledge of food-web dynamics is particularly urgent given that fish stocks are collapsing and fisheries sustain the livelihoods of a significant part of the human population. This thesis addresses the trophic interactions of the marine community of the Bijagós Archipelago, Guinea-Bissau. The extensive mangroves and mudflats of this continental archipelago make it an important area for several migratory species (e.g. marine turtles, waders) and resident species (e.g. seabirds), as well as a nursery area for several fish species. The great biodiversity value of the Bijagós led it to be declared as UNESCO Biosphere Reserve in 1996 and a Ramsar site in 2014. Nevertheless, few studies have been conducted in its marine ecosystem. Seasonal, lunar tidal and diel variations of the coastal small fish community of the Bijagós Archipelago were studied through beach seining along spatial and temporal scales. The diet and foraging behaviour of marine predators (predatory fishes and seabirds) was also studied, with particular interest in their facilitative feeding associations. Traditional methods were used for diet description, such as, the macroscopic identification of prey remains from stomach contents of predatory fish and pellets of breeding seabirds. We also used next-generation sequencing, employing DNA metabarcoding on the identification of prey in the droppings of wintering seabirds. This was the first time this method was used for studying the feeding ecology on migratory birds in their wintering quarters. Additionally, behavioural focal observations of seabirds were performed to investigate their feeding habits. Given the lack of previous descriptive studies, this work also focuses the particularities of length-weight relationships of six fish species. The present study showed that the marine ecosystem of the Bijagós is strongly dominated by a small pelagic fish species, Sardinella maderensis. This species was the most abundant throughout the year as well as in all the islands, and the most frequent item in the diet of all marine predators. In regards to facilitative foraging, different species of seabirds showed distinctive degrees of reliance on associations, ranging from completely independent to near-obligatory. The results also suggest that the use of associations influences the distribution of seabird species and may enhance their foraging success. The overall findings presented here indicate that the marine ecosystem of the Bijagós Archipelago is a wasp-waist type, with Sardinella maderensis as the key small pelagic species, and that an ecosystem-based approach must be considered for the adequate management of the archipelago. Declines in populations of predatory fish and small pelagic fish are both likely to influence the distribution and foraging success of seabirds, with impacts on their survival and breeding success. |
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