Streamlining baited remote underwater video surveys to assess the fish community in the desertas islands nature reserve, Madeira

Graça, António Carlos da Costa

http://hdl.handle.net/10400.12/10334

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Authors

Graça, António Carlos da Costa

Advisor(s)

Alves, Filipe

Abstract(s)

ABSTRACT: To guide the development of efficient and effective management plans it is crucial to implement an appropriate sampling technique that provides a comprehensive assessment, whilst mitigating potential biases. This project aims to attain a streamlined approach to assess fish communities in sub-tropical coastal areas by eliminating unnecessary steps, reducing complexity, and optimizing workflow. Thus, we sought out to discover (1) how the fish assemblage composition relates to the deployment time and (2) if it interacts with substrate type, affecting the assemblage. We then compared the current methodology, which involves 60-minute surveys of BRUV (Baited Remote Underwater Video), with the alternative, that proposes conducting only 30-minute surveys. Our focus was on the surrounding coastal habitats of the Desertas islands, which have been recognized as being vital for the Mediterranean monk seal, Monachus monachus, sub-population that inhabits this area. This species is regarded as one of the most endangered marine mammal species worldwide, and, in the Northeastern Atlantic, the Madeira archipelago stands as one of their last sanctuaries. Our results show that while longer deployments tended to detect a higher number of species, the overall community structure, or species assemblage, was not significantly different when comparing the 30-minute and 60-minute observation periods. From a conservation management perspective this implies that shorter BRUV deployments can be an effective tool for routine monitoring, particularly of prey species that are of interest in maintaining the ecological balance, whilst simultaneously supporting predator species such as the Mediterranean monk seal. Furthermore, most of the deployments in consolidated substrate (rock) presented higher abundance and diversity in comparison with the deployments made in unconsolidated substrate (sand). We advocate for the adoption of shorter BRUV deployments in routine fish community monitoring, signifying a methodological shift that can lead to more agile and responsive conservation management strategies. This promotes also the assessment of existing approaches for BRUVs use in conservation, which aligns with the broader goals of sustainable resource use and biodiversity conservation, ensuring that we remain vigilant guardians of our marine ecosystems while optimizing our methods to the rhythm of the natural world we aim to protect. Balancing efficiency with comprehensiveness is the key, therefore, conservation plans should be tailored to the specific objectives of the monitoring program considering the target species, habitat type, and ecological questions at hand.