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Key exploited species as surrogates for coastal conservation in an oceanic archipelago: insights from topshells and limpets from Madeira (NE Atlantic Ocean)
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Abstract(s)
As lapas e os caramujos estão entre os herbívoros mais bem adaptados ao intertidal do Atlântico
Nordeste. Estas espécies-chave fornecem serviços ecossistémicos valiosos, desempenhando um papel
fundamental no equilíbrio ecológico do intertidal e têm um elevado valor económico, estando sujeitas
a altos níveis de exploração e representando uma das atividades económicas mais rentáveis na pesca
de pequena escala no arquipélago da Madeira. Esta dissertação visa preencher as lacunas existentes
na história de vida e dinâmica populacional destas espécies, e aferir os efeitos da regulamentação da
apanha nos mananciais explorados. A abordagem conservacionista implícita ao longo desta tese
pretende promover: (i) a regulamentação adequada da apanha de caramujos (Phorcus sauciatus) e (ii)
a avaliação dos efeitos da regulamentação da apanha de lapas nas populações exploradas (Patella
aspera, Patella candei). Atualmente, os mananciais de lapas e caramujos são explorados perto do
rendimento máximo sustentável, e a monitorização e fiscalização são fundamentais para evitar a
futura sobre-exploração. A regulamentação da apanha de lapas produziu um efeito positivo nas
espécies de lapas exploradas, com um aumento no tamanho, na proporção de indivíduos
reprodutores, no tamanho de maturação e num maior equilíbrio na proporção de sexos. A apanha de
caramujos não está regulamentada e com o atual nível de exploração ocorrem alterações na estrutura
de tamanhos, abundância e potencial reprodutivo das populações exploradas, pelo que urge
implementar a regulamentação da apanha desta espécie, por forma a mitigar os efeitos negativos
desta atividade. O efeito da proximidade das populações humanas e acessibilidade costeira na
estrutura de tamanhos e abundância de gastrópodes explorados mostrou que a proporção de
reprodutores e a abundância eram geralmente menores em áreas mais próximas das populações
humanas e em áreas mais acessíveis. Os efeitos das Áreas Marinhas Protegidas na proteção das
populações de lapas resultaram num aumento diferencial do tamanho, da maturidade sexual e da
captura por unidade de esforço de acordo com o grau de proteção. O esclarecimento e envolvimento
das comunidades locais, reguladores, decisores políticos e partes interessadas, baseados em
informação e educação, são cruciais para uma gestão eficaz e sustentável destes gastrópodes marinhos
e ecossistemas a médio e longo prazo.
Limpets and topshells are among the most successful intertidal grazers in the North-eastern Atlantic. These keystone species play a pivotal role in structuring rocky shores communities, and provoding valuable ecosystem services. Than have an important economic value, being subject to high levels of exploitation and representing one of the most profitable economic activities in small-scale fisheries in the archipelago of Madeira. This thesis aims to fill the gaps on the life-traits and population dynamics of these species, and assess the effects of harvesting regulations on the exploited stocks. A focus on conservation is implicit throughout this thesis since it addresses the promotion of: (i) proper regulation of the unregulated harvesting of topshells (Phorcus sauciatus) and (ii) provide additional information on the effects of harvesting regulations on limpets (Patella aspera, Patella candei). Currently, limpets and topshells stocks are being exploited near the maximum sustainable yield and monitoring and enforcement must be accomplished to avoid future overexploitation. Conservation measures prompted a positive effect on both exploited limpet species with an increase in length, reproductive individuals, size-at-first maturity and a more balanced sex-ratio after harvesting regulations. The harvesting of topshells is not regulated and with the current level of exploitation there are changes in the size structure, abundance and reproductive potential of the exploited populations, so it is imperative to implement the harvesting regulations for this species, in order to mitigate the negative effects of harvesting. The effect of proximity to human settlements and coastal accessibility on the size-structure and abundance of exploited gastropods showed that the mean-size, proportion of reproductive individuals and abundance were generally smaller in areas closer to human settlements and in more accessible areas. The effects of protection from the Marine Protected Areas on limpet populations resulted in a differential increase on size, size-at-first maturity and catch-per-unit-effort according to the degree of protection. The understanding and commitment of local communities, regulators, policymakers and stakeholders, based on information and education are crucial to the effective management and to ensure the sustainability of these marine gastropods and ecosystems at medium and long term.
Limpets and topshells are among the most successful intertidal grazers in the North-eastern Atlantic. These keystone species play a pivotal role in structuring rocky shores communities, and provoding valuable ecosystem services. Than have an important economic value, being subject to high levels of exploitation and representing one of the most profitable economic activities in small-scale fisheries in the archipelago of Madeira. This thesis aims to fill the gaps on the life-traits and population dynamics of these species, and assess the effects of harvesting regulations on the exploited stocks. A focus on conservation is implicit throughout this thesis since it addresses the promotion of: (i) proper regulation of the unregulated harvesting of topshells (Phorcus sauciatus) and (ii) provide additional information on the effects of harvesting regulations on limpets (Patella aspera, Patella candei). Currently, limpets and topshells stocks are being exploited near the maximum sustainable yield and monitoring and enforcement must be accomplished to avoid future overexploitation. Conservation measures prompted a positive effect on both exploited limpet species with an increase in length, reproductive individuals, size-at-first maturity and a more balanced sex-ratio after harvesting regulations. The harvesting of topshells is not regulated and with the current level of exploitation there are changes in the size structure, abundance and reproductive potential of the exploited populations, so it is imperative to implement the harvesting regulations for this species, in order to mitigate the negative effects of harvesting. The effect of proximity to human settlements and coastal accessibility on the size-structure and abundance of exploited gastropods showed that the mean-size, proportion of reproductive individuals and abundance were generally smaller in areas closer to human settlements and in more accessible areas. The effects of protection from the Marine Protected Areas on limpet populations resulted in a differential increase on size, size-at-first maturity and catch-per-unit-effort according to the degree of protection. The understanding and commitment of local communities, regulators, policymakers and stakeholders, based on information and education are crucial to the effective management and to ensure the sustainability of these marine gastropods and ecosystems at medium and long term.
Description
Keywords
Caramujos Phorcus sauciatus Lapas Patella aspera Patella candei Patella piperata Parâmetros biológicos Estrutura populacional Regulamentação Áreas marinhas protegidas Exploração sustentável Intertidal Arquipélago da Madeira (Portugal) Atlântico Nordeste Topshells Life-traits Population structure Harvesting regulations Marine protected areas Sustainable exploitation Intertidal Madeira archipelago (Portugal) North-eastern Atlantic Biological Sciences . Faculdade de Ciências Exatas e da Engenharia