High Coral Cover Offsets the Impacts of High Fishing Pressure on Fish Biomass in a Remote Coral Reef System

ABSTRACT

Illegal fishing and habitat degradation threaten coral reef biodiversity throughout the South China Sea. At Dongsha Atoll, a remote but heavily exploited national park, the lack of traditional monitoring has hindered our understanding of how fishing pressure interacts with habitat quality to influence the fish communities. We used coastal surveillance radar systems (CSRS) to quantify pressure from ‘dark fishing fleets’ (those without Automatic Identification Systems) and integrated this with underwater visual surveys of fish biomass, abundance and richness. Generalized Additive Models (GAMs) revealed a consistent interaction between fishing pressure and habitat complexity ( p  < 0.05); at sites with low coral cover (< 20%), fish biomass and abundance exhibited precipitous declines as boat density increased (β ≈ −0.30). Meanwhile, at sites with high coral cover (> 50%), these community metrics remained stable, indicating that structural complexity provides a critical buffer against exploitation. Despite formal protection of the reefs at Dongsha, we observed a pervasive shift in community composition; large‐bodied predators and herbivores were severely depleted across the atoll, regardless of local fishing pressure. These findings demonstrate that while habitat health can mitigate some impacts of illegal fishing, formal protection is insufficient without active enforcement. We show that CSRS provides a high‐resolution, objective tool for monitoring illegal fishing activity in remote areas, offering a scalable method for linking anthropogenic pressure to ecological resilience in contested maritime regions.