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Spatial behaviour and nesting dynamics of green turtles in a west african marine protected area
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Compreender a distribuição espacial e a dinâmica de nidificação das tartarugas marinhas, um grupo carismático de megafauna marinha, é fundamental para a sua conservação, especialmente no caso de grandes populações que se concentram num único local de idificação geograficamente restritivo e para as quais ainda existem lacunas de conhecimento. O Parque Nacional Marinho João Vieira e Poilão (doravante ‘PNMJVP’), uma área marinha protegida localizada no sudeste do Arquipélago dos Bijagós, na Guiné-Bissau, abriga uma das maiores populações de tartarugas-verdes Chelonia mydas do mundo, sendo que a maior parte dos ninhos está concentrada na pequena e isolada ilha de Poilão. Nesta tese de doutoramento, avaliei parâmetros ecológicos essenciais da população de tartarugasverdes do PNMJVP. Inicialmente, foquei-me nos movimentos de fêmeas reprodutoras no
período entre desovas para investigar a sua distribuição espacial, fidelidade ao local e conexões entre ilhas do PNMJVP. De seguida, estimei o sucesso reprodutor na ilha de Poilão e nas restantes três principais ilhas do PNMJVP, com base na análise de dados previamente recolhidos sobre a sobrevivência dos ninhos e respetivas ameaças, como a predação e a inundação. Posteriormente, examinei o aporte de nutrientes proveniente dos ovos e tartarugas recém-eclodidas nas comunidades costeiras do PNMJVP. Para alcançar estes objetivos, foram utilizados vários métodos, como a marcação e o seguimento de tartarugas com recurso a anilhas e dispositivos de localização eletrónicos, respetivamente, e a quantificação de isótopos estáveis. Os resultados mostraram que as tartarugas-verdes ermaneceram numa área restrita ao redor de Poilão durante o período entre desovas, com cerca de metade do seu território incluído na zona central de proteção integral do PNMJVP, demonstrando uma forte fidelidade aos locais de permanência entre desovas. A predação e a inundação dos ninhos de tartaruga-verde no PNMJVP foram mais elevadas nas ilhas adjacentes a Poilão, verificando-se um número limitado de conexões entre as principais ilhas do PNMJVP pelas
tartarugas. Isto sugere uma possível dinâmica fonte-sumidouro, em que as ilhas com baixa produção de descendência funcionam como habitats sumidouros utilizados por indivíduos que migram de Poilão (fonte), que atualmente oferece as melhores condições para a sobrevivência dos ninhos. Localmente, as tartarugas-verdes contribuem com nutrientes para o ecossistema costeiro de Poilão, beneficiando principalmente as espécies localizadas diretamente nos
locais de nidificação ou na sua proximidade. Por último, apresento a primeira revisão sobre o comportamento de fidelidade aos locais de reprodução e alimentação das tartarugas marinhas. Nesta revisão, identifico lacunas no conhecimento atual e destaco como a
investigação científica no futuro pode abordar estas questões, além da necessidade de adotar um conceito padronizado de fidelidade ao local em estudos futuros. Esta tese contém dados sobre o comportamento e a ecologia das tartarugas-verdes no PNMJVP, que podem informar os gestores do parque sobre o planeamento espacial marinho e a priorização de esforços de conservação, de forma a apoiar a preservação das tartarugas marinhas.
Understanding the spatial distribution and nesting dynamics of sea turtles, a charismatic group of marine megafauna, is critical for their conservation. This is particularly important for some major sea turtle populations that aggregate at one specific geographically restricted nesting site and for which this knowledge remains incomplete. The João Vieira-Poilão Marine National Park (hereafter ‘JVPMNP’), a marine protected area located southeast of the Bijagós Archipelago in Guinea-Bissau, hosts one of the world’s largest green turtle Chelonia mydas breeding aggregations, but most of the nesting concentrates on the small and isolated island of Poilão. In this PhD thesis, I assessed key ecological parameters of the JVPMNP green turtle population. I first focused on the inter-nesting movements of breeding female green turtles to assess their spatial distribution, site fidelity, and inter-island linkages within the JVPMNP. Next, I estimated the reproductive success at Poilão and its 3 neighbouring islands within the JVPMNP, through the analyses of previously collected datasets on green turtle clutch survival and associated threats (predation and flooding). Following this, I examined the nutrient input from green turtle eggs and hatchlings into the coastal communities of the JVPMNP. To achieve these goals, several methods were employed, including sea turtle tagging and tracking, and the quantification of stable isotopes. Green turtles remained within a restricted area around Poilão during their inter-nesting intervals, with about half of their home range falling within the central no-take zone, and showing strong fidelity to inter-nesting sites. Clutch predation and flooding were higher on Poilão’s neighbouring islands, with limited turtle exchanges between JVPMNP islands. This suggests a possible source-sink dynamic where islands with low reproductive output are sink habitats, used by migrants from Poilão (source), which currently offers the best conditions for clutch survival. On a local scale, green turtles contribute nutrients to the coastal ecosystem of Poilão, mainly benefiting species located directly at or in close proximity to sea turtle nesting sites. Lastly, I provide the first review of sea turtle breeding and foraging site fidelity, identifying gaps in the current knowledge and highlighting how future research can address these gaps, as well as the need for the adoption of a standardized concept of site fidelity in future studies. This work offers new insights into the behaviour and ecology of green turtles in the JVPMNP, providing valuable information to decision-makers for marine spatial planning and prioritizing conservation efforts, thereby supporting sea turtle conservation.
Understanding the spatial distribution and nesting dynamics of sea turtles, a charismatic group of marine megafauna, is critical for their conservation. This is particularly important for some major sea turtle populations that aggregate at one specific geographically restricted nesting site and for which this knowledge remains incomplete. The João Vieira-Poilão Marine National Park (hereafter ‘JVPMNP’), a marine protected area located southeast of the Bijagós Archipelago in Guinea-Bissau, hosts one of the world’s largest green turtle Chelonia mydas breeding aggregations, but most of the nesting concentrates on the small and isolated island of Poilão. In this PhD thesis, I assessed key ecological parameters of the JVPMNP green turtle population. I first focused on the inter-nesting movements of breeding female green turtles to assess their spatial distribution, site fidelity, and inter-island linkages within the JVPMNP. Next, I estimated the reproductive success at Poilão and its 3 neighbouring islands within the JVPMNP, through the analyses of previously collected datasets on green turtle clutch survival and associated threats (predation and flooding). Following this, I examined the nutrient input from green turtle eggs and hatchlings into the coastal communities of the JVPMNP. To achieve these goals, several methods were employed, including sea turtle tagging and tracking, and the quantification of stable isotopes. Green turtles remained within a restricted area around Poilão during their inter-nesting intervals, with about half of their home range falling within the central no-take zone, and showing strong fidelity to inter-nesting sites. Clutch predation and flooding were higher on Poilão’s neighbouring islands, with limited turtle exchanges between JVPMNP islands. This suggests a possible source-sink dynamic where islands with low reproductive output are sink habitats, used by migrants from Poilão (source), which currently offers the best conditions for clutch survival. On a local scale, green turtles contribute nutrients to the coastal ecosystem of Poilão, mainly benefiting species located directly at or in close proximity to sea turtle nesting sites. Lastly, I provide the first review of sea turtle breeding and foraging site fidelity, identifying gaps in the current knowledge and highlighting how future research can address these gaps, as well as the need for the adoption of a standardized concept of site fidelity in future studies. This work offers new insights into the behaviour and ecology of green turtles in the JVPMNP, providing valuable information to decision-makers for marine spatial planning and prioritizing conservation efforts, thereby supporting sea turtle conservation.
Description
Thesis presented in fulfilment of the degree of PhD in Behavioural Biology, Instituto Universitário de Ciências Psicológicas, Sociais e da Vida, presented at Ispa – Instituto Universitário de Ciências Psicológicas, Sociais e da Vida .
Keywords
Tartaruga-verde Distribuição espacial Desova Área marinha protegida Green turtle Spatial distribution Nesting Marine protected area