Underwater soundscape analysis reveals fish assemblage contrasts between protected and exploited areas in an African mangrove delta

Mangrove estuaries are keystone habitats for many marine species, but their contribution to the tropical coastal fisheries is threatened by increasing anthropogenic pressures, including overfishing. Thus, the implementation of marine protected areas in mangroves is motivated by the need to ensure the fishing community's food security and economic livelihood, but there is a lack of affordable methods to monitor the effect of this management on fish. Here, we explored how passive acoustic monitoring (PAM) could be utilized in a case study of the Sine-Saloum estuary, Senegal. We compared biodiversity indices based on PAM and scientific fishing in two contrasted areas, one being heavily fished and the other protected. We computed fish sound abundance, richness, and diversity indices from underwater recordings in both areas in 2020 and 2024, and compared them to those obtained from conventional fish sampling methods. Acoustic-based indices were in accordance with fishing-based indices and showed anticipated differences between protected vs. exploited areas. This first PAM assessment in underwater mangrove suggests it might be a useful tool for MPA monitoring in this type of habitats, and open the way to continuous, fishery-independent, non-intrusive fish assemblage monitoring system. Such monitoring system would contribute to the establishment and acceptance of protected areas in mangroves ecosystems.