Browsing by Issue Date, starting with "2024-10-23"
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- An ecological assessment of fish recruitment in Lagos through the monitoring of BiohutsPublication . Berimbau, Luís Martim Almada; Erzini, KarimMarine ecosystems are crucial hubs of biodiversity and face increasing threats from human activities, particularly in coastal areas serving as nurseries for fish recruitment, a pivotal factor influencing the abundance and diversity of fish populations. This study focuses on evaluating the abundance, biodiversity and recruitment dynamics through an underwater visual census, with a specific focus on the innovative Biohut structures installed in Marina de Lagos and their potential contribution to marine biodiversity conservation. This study focused on ecological processes such as habitat association and the impact of environmental and biological factors, and assessed the Biohuts potential to enhance abundance, biodiversity and recruitment. The methodology employed underwater visual censuses and environmental data collection for a comprehensive assessment from September 2023 to June 2024. The period between spring and early summer had the highest values in terms of abundance of recruits. The results indicate that the Biohuts significantly increased fish abundance, biodiversity and recruitment when compared with the control areas inside and outside the marina. In conclusion, Biohuts are effective tools for enhancing fish abundance, biodiversity, and recruitment in urbanized coastal areas. They provide a promising solution for habitat restoration, marine biodiversity conservation and can also serve as platforms to study key processes for sustainable management of fisheries as it is the case of fish recruitment.
- Spatio-temporal dynamics of soft bottom fishes in the Luiz Saldanha Marine Park: Effectiveness of spatial protection and movement ecology of vulnerable speciesPublication . Sousa, Inês Isabel Gralho Correia de; Erzini, Karim; Gonçalves, Jorge M.S.; Gonçalves, Emanuel J.This thesis explores the effectiveness of the Professor Luiz Saldanha Marine Park (PLSMP) in Portugal, a coastal Marine Protected Area (MPA) in the north-eastern Atlantic, for conserving and managing soft-bottom fish species, including several elasmobranchs. The approach employed several methodologies, mainly experimental fishing and acoustic telemetry, to provide a comprehensive understanding of species' responses to spatial protection measures. The work presented in Chapter I investigates the response of soft-bottom fishes to spatial protection within the PLSMP. Specifically, analyses of abundance, biomass, and total lengths of these fishes during and after the implementation of the MPA’s management plan are presented. Results suggest that the community is primarily structured by depth and substrate, followed by protection level. Community composition analyses demonstrated significant differences between protection levels and over time. It is hypothesised that species-specific factors, such as habitat preferences or body size may influence the potential of benefiting from spatial protection. Overall, the chapter reports some evidence of the protection's effectiveness, based on the increased biomass in protected areas and the positive trends of certain species. This thesis also dedicates particular focus on the study of skates, given their vulnerability and conservation concerns. Chapter III focuses on the thornback ray (Raja clavata). The PLSMP offered a valuable case study for assessing the effectiveness of spatial protection for this species. Using experimental fishing, conventional tagging, and acoustic telemetry, the study found that thornback rays are more abundant in the higher protection areas, and several individuals were classified as residents in the area (acoustic telemetry data). Significant increases in adult and juvenile abundance over time were observed, although juveniles also exhibited a decrease in the later years of sampling. Acoustic telemetry data suggest seasonal trends, with higher residency in spring and summer and expanded utilization areas in autumn. Potential vulnerabilities are highlighted, such as the mature males preference for the offshore area of the marine reserve, and frequent excursions to outside the protected area, suggesting some susceptibility to fishing. Chapter IV examines the spatial dynamics of the endangered undulate ray (Raja undulata) within the PLSMP. Acoustic telemetry data collected over three years indicated variability in residency among individuals. High site fidelity was observed in half of the tracked individuals, and the species seems to equally use both offshore and inshore areas within the MPA. Evidence is that both males and females may be recurrent users of this protected area. Compared with other ray species (Chapter III), the undulate ray seems to undertake less excursions to outside the MPA. These results suggest that the PLSMP may offer protection benefits for this species. However, adequate management measures for the conservation of the undulate ray are still depending on further research, to further understand its seasonal patterns and its patchy distribution. Chapter V presents preliminary insights into the movement patterns of the regionally critically endangered white skate (Rostroraja alba). Acoustic telemetry was used to monitor three individuals in the PLSMP. The mature female exhibited high residency, spending over 70% of the time within the marine park, while the two immature individuals were detected for shorter periods. The study's findings, although limited by the small sample size, provide useful suggestions for future research on this poorly understood species. In the current era of challenges for the marine environment, it is important to use MPAs as a tool to preserve marine biodiversity, including soft-substrate fish species. Overall, the findings presented in this thesis emphasize that the PLSMP has the potential to provide effective protection for the soft-bottom fish communities. The findings regarding the skates case studies also indicate that the PLSMP may offer protection benefits to these species. Nevertheless, the aspect of habitat continuity should be taken into account in the management of this and other MPAs aiming to protect soft-bottom communities. Furthermore, to apply fishing effort regulation measures in the adjacent areas of the marine reserve would likely enhance protection effectiveness. Other important factors for the success of the PLSMP and other MPAs include the integration of management institutions and stakeholders, as well as continuous monitoring of ecological and social indicators. The obtained data, along with previous work, underscore the importance of implementing measures to improve MPA effectiveness. To promote compliance through surveillance and stakeholder engagement is expected to contribute positively to the success of the PLSMP. This MPA is located in an important area to support connectivity of coastal habitats along the Portuguese coast and beyond. Adopting an adaptive approach for the management of the PLSMP would likely enhance its ability to contribute to the long-term sustainability and connectivity of marine ecosystems.