Abstract:

Aims: This study aims to evaluate the effectiveness of the Baited Remote Underwater Video (BRUV) technique in monitoring nearshore reef fish communities in the Nanpeng Archipelago, China, and to compare its performance with the traditional Underwater Visual Census (UVC) method. The focus is on assessing both techniques in terms of species diversity, composition, and their ability to capture different ecological groups of reef fish. 

Methods: Simultaneous BRUV and UVC surveys were carried out at four coral reef sites. Each BRUV unit, baited with 2 kg of chopped clupeoid fish (Clupea sp), was deployed until the camera was out of battery. UVC surveys were done by divers recording fish species and abundances along transects. Functional diversity was assessed using traits such as body size, trophic level, mobility, gregariousness, water column, and diet. 

Results: BRUV and UVC recorded a similar number of species (59 for BRUV vs. 61 for UVC), but BRUV exhibited a higher functional richness index (0.987 vs. 0.783). Functional trait analysis showed that BRUV was more effective at capturing large-bodied, highly mobile, schooling predators such as Caranx sexfasciatus, whereas UVC detected a higher number of cryptic reef-associated species. Analysis of species accumulation curves indicated an optimal BRUV deployment duration of 50-60 minutes, beyond which additional sampling time yielded diminishing returns in species detection. 

Conclusions: Both BRUV and UVC have distinct strengths and limitations in monitoring reef fish communities. Our findings demonstrate that BRUV and UVC exhibit distinct yet complementary monitoring efficiencies: UVC is more effective for monitoring fish communities in coral-rich reefs, while BRUV performs better in monitoring rocky reef fish diversity. In practical applications, a combination of both methods would provide a more comprehensive understanding of reef fish diversity and ecological function.

Key words: Baited Remote Underwater Video (BRUV), Underwater Visual Census (UVC), Nanpeng Archipelago, reef fish, species composition, functional structure