Bait increases the precision in count data from remote underwater video for most subtidal reef fish in the warm-temperate Agulhas bioregion

Baited remote underwater video (BRUV) has been identified in the literature as a powerful long-term monitoring tool for subtidal rocky reef fish communities. To test this, a repeated-measures field experiment comparing unbaited remote underwater video (RUV) with BRUV was conducted in the Tsitsikamma National Park Marine Protected Area between June 2008 and February 2010. The results demonstrate that BRUV was more efficient at surveying the entire fish community, specifically invertebrate carnivores, generalist carnivores and cartilaginous species. On the other hand, RUV was more effective at surveying microinvertebrate carnivores. High variability in the RUV data resulted in the method requiring a greater number of samples to achieve the same diagnostic power as BRUV. However, RUV required a shorter deployment and post-sampling video analysis time, making it more time efficient. Baited remote underwater video was more sensitive in the detection of differences in abundance between habitat types, while the RUV data were more prone to an intra-species methodological bias linked to the percentage of reef visible in the frame of view. The scale of the response to the presence of bait was inconsistent among species, indicating that behaviour determined the area surveyed within the bait plume of BRUV. The benefits gained by sampling the fish community with RUV do not outweigh those obtained by altering the community through the presence of bait. However, in combination, the 2 methods are highly effective at monitoring the subtidal fish communities in the Agulhas bioregion of South Africa.