Cost-efficient sampling of fish assemblages: comparison of baited video stations and diver video transects

Baited remote underwater stereo-video (stereo-BRUV) stations and diver operated stereo-video (stereo-DOV) transects are increasingly used to sample both tropical and temperate fish assemblages. Compared to in situ visual census methods, the use of stereo-video reduces inter- observer variability, improves definition of the sample unit area, increases accuracy of fish length estimates and provides a permanent record of the assemblage that can be validated where required or independently reanalysed. Previous studies have suggested that stereo-BRUV collects representa- tive data on both carnivorous and herbivorous species and can be more cost-efficient than diver- based survey methods. This study compares estimates of common fish assemblage metrics obtained with stereo-BRUV stations and stereo-DOV transects across 3 biogeographic regions, and uses a cost- optimization procedure to compare the efficiency of these 2 methods. Stereo-BRUV stations were found to sample greater species richness and obtain greater estimates of relative biomass of general- ist carnivores, but no differences occurred in the biomass of herbivores sampled by the 2 techniques. Stereo-BRUV stations generally obtained estimates of assemblage metrics with less variance, result- ing in greater power to detect spatial and temporal changes in the fish assemblage metrics. Cost-benefit analyses found that stereo-BRUV was generally more time efficient than stereo-DOV transects in terms of smaller standard error around the mean of the various metrics considered. How- ever, across the 3 biogeographic regions sampled there was considerable variation in the magnitude of these differences. Results suggest that stereo-BRUV stations are, in general, a more cost-effective method for monitoring fish assemblages than stereo-DOV transects.