A comparison of underwater visual census, baited, diver operated and remotely operated stereo-video for sampling shallow water reef fishes

Marine Protected Areas (MPAs) are a popular conservation strategy aimed at managing anthropogenic pressures and protecting habitats and the diversity of ocean flora and fauna. Robust, cost-effective sampling of fish as-semblages is important in understanding the effects of these management strategies on ocean ecosystems. We compared the sampling effectiveness and efficiencies of three commonly used methods of sampling fish as-semblages; underwater visual census (UVC), baited remote underwater stereo-video systems (stereo-BRUVs), and diver operated stereo-video (stereo-DOV) and one emerging method (remotely operated vehicle with stereo -video system (stereo-ROV). We assessed the assemblage composition, numbers of species and individuals, and the statistical power to detect hypothetical changes in the number of species and individuals for each method. Stereo-BRUVs sampled a distinctive assemblage compared to all transect-based methods, with more in-dividuals, total species, and predatory fishes from higher trophic groups that are targeted by commercial and recreational fishers. UVC also sampled a distinctive assemblage compared to stereo-ROV and stereo-BRUVs (comparisons with stereo-DOV were not possible due to sampling restrictions). The fish assemblage sampled by UVC consisted of more species and individuals than stereo-ROV and small bodied or cryptic species that were not detected by the video methods. Although stereo-DOV sampled more individuals than stereo-ROV with dif-ferences in small schooling species at a few sites, the assemblage composition was broadly comparable. To effectively monitor MPAs a combination of BRUVs, which more effectively sampled fisheries indicator species, and one of the transect based methods should be used. Given the similarities in the assemblages sampled by the stereo-video transect based methods and the advantages associated with health and safety, logistics and field efficiency with remote methods, we recommend stereo-ROV and stereo-BRUVs.

Automated summary

This study compared the sampling effectiveness and efficiencies of four commonly used methods for sampling fish assemblages in marine protected areas (MPAs). The results showed that stereo-BRUVs sampled a distinctive assemblage with more individuals, total species, and predatory fishes. UVC sampled a distinctive assemblage with more species and individuals, including small bodied or cryptic species. Based on the sampling results and advantages, stereo-ROV and stereo-BRUVs were recommended for monitoring MPAs.