Sharks and rays in troubled waters: Threatened species in dynamic intertidal ecosystems

This thesis investigates the impact of fisheries on the role of sharks and rays as predators in large intertidal areas, with a focus on the Banc d'Arguin (Mauritania) and the Bijagós Archipelago (Guinea-Bissau). Through a multidisciplinary approach, I address how fisheries affect these species, their potential interactions with other predators, and the consequences of their removal for ecosystem functioning.
Findings reveal a severe decline in shark and ray populations in both study areas, likely due to the combined effects of industrial and small-scale fisheries operating on the border and within these protected areas, respectively. This has led to changes in shark and ray communities and catches of fisheries. This thesis shows that highly threatened hammerhead sharks and guitarfish still use these areas but that continued exploitation will likely cause these to disappear. Moreover, this research underscores the importance of the intertidal habitat for sharks and rays as feeding refugia or nurseries. This also highlights their role in ecosystem functioning and interactions with migratory shorebirds, as an overlap between prey species of rays and shorebirds suggests their shared reliance on intertidal prey.
The thesis underlines the need to include intertidal areas as ecologically important areas for sharks and rays in conservation and emphasizes the importance of community involvement in data collection and management strategies. Recommendations include improving data collection, identifying areas for protection, and enforcing fishing regulations. The integration of shark and ray protection is urgently needed to halt their continued loss from these vital ecosystems and associated coastal livelihoods.