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Small pelagics, predatory fish and seabirds : trophic and behavioural interactions in a marine protected area in Guinea-Bissau

Publication . Correia, Edna Rita de Freitas da Costa; Granadeiro, José Pedro, 1964-; Catry, Paulo Xavier, 1968-

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.

2018Doctoral thesis

Open access

Combined impacts of climate and socio-economic scenarios on irrigation water availability for a dry Mediterranean reservoir

Publication . Nunes, João Pedro; Jacinto, Rita; Keizer, Jacob

The impacts of climate and associated socio-economic changes on water availability, including supply and demand, quality, and storage volume, were evaluated for the Vale do Gaio reservoir in southern Portugal, located in a dry Mediterranean climate and already under drought stress. The SWAT model was applied with 6 scenarios for 2071-2100, involving two storylines (A1B and B1) with individual changes in climate (-9% rainfall, increasing in winter by +28 to +30%), socio-economic conditions (an increase in irrigation demand by 11%, and a replacement of cereals and pastures by sunflower), and a combination of both. Most future scenarios resulted in lower water availability, due to lower supply (-19 to -27%) combined with higher irrigation demand (+3 to +21%). This resulted in more years with limited irrigation supplies (presently: 28%; scenarios: 37 to 43%), although limitations were mitigated by lower losses to excess discharge. Land-use changes also decreased quality by increasing P concentrations (+29 to +93%). Impacts were more severe in scenario A1B than in B1, and in combined changes than in climate or socio-economic changes only. Water availability was resilient to climate change, as impacts led only to a moderate aggravation of present-day conditions. Lower future water availability could be addressed by supply and demand management strategies and, in the most extreme scenario, by water transfers from regional water reserves; water quality issues could be addressed through land-use policies. Results also highlighted the importance of taking the characteristics of water supply systems into account when designing adaptation measures for future changes.

2017-02-20Journal article

Open access

Mapping Knowledge Gaps of Mozambique’s Terrestrial Mammals

Publication . Neves, Isabel Queirós; Mathias, Maria da Luz; Bastos-Silveira, Cristiane

A valuable strategy to support conservation planning is to assess knowledge gaps regarding primary species occurrence data to identify and select areas for future biodiversity surveys. Currently, increasing accessibility to these data allows a cost-effective method for boosting knowledge about a country's biodiversity. For understudied countries where the lack of resources for conservation is more pronounced to resort to primary biodiversity data can be especially beneficial. Here, using a primary species occurrence dataset, we assessed and mapped Mozambique's knowledge gaps regarding terrestrial mammal species by identifying areas that are geographically distant and environmentally different from well-known sites. By comparing gaps from old and recent primary species occurrence data, we identified: (i) gaps of knowledge over time, (ii) the lesser-known taxa, and (iii) areas with potential for spatiotemporal studies. Our results show that the inventory of Mozambique's mammal fauna is near-complete in less than 5% of the territory, with broad areas of the country poorly sampled or not sampled at all. The knowledge gap areas are mostly associated with two ecoregions. The provinces lacking documentation coincide with areas over-explored for natural resources, and many such sites may never be documented. It is our understanding that by prioritising the survey of the knowledge-gap areas will likely produce new records for the country and, continuing the study of the well-known regions will guarantee their potential use for spatiotemporal studies. The implemented approach to assess the knowledge gaps from primary species occurrence data proved to be a powerful strategy to generate information that is essential to species conservation and management plan. However, we are aware that the impact of digital and openly available data depends mostly on its completeness and accuracy, and thus we encourage action from the scientific community and government authorities to support and promote data mobilisation.

2019-12-03Journal article

Open access