Application of spatially robust stereo-BRUV sampling for quantifying fish assemblages in UK marine protected areas.

Marine protected areas (MPAs) often lack adequate data on the status of marine assemblages to support evidence-based management. Stereo baited remote underwater video (BRUV) systems offer a powerful, low-cost tool for collecting ecological data, yet they remain underutilized in the North East Atlantic, especially compared to more invasive methods such as fisheries surveys. Here, we demonstrate how a spatially comprehensive stereo-BRUV survey can generate benchmark data to support MPA management at an ecosystem scale, using an ecologically distinct oceanic archipelago as a case study. The archipelago's habitats were found to support high abundances of regionally targeted commercial species, including benthic catsharks (Scyliorhinidae) and European spiny lobster (Palinurus elephas), with ~12,000 individuals recorded representing 64 species and 44 families. Deeper, topographically complex reefs were found to support higher levels of richness and biomass, with sediment-specific increases in depth also driving demersal abundance. Stereo technology was additionally able to provide body size data for 43 species, with remoteness and shelter from exposure found to be common drivers of increased body size for indicator taxa. Survey results represent a contemporary benchmark for measuring changes in local MPA management, fisheries practices, and climate change impacts. The results also illustrate how spatially robust sampling methods and stereo-BRUV systems can facilitate more holistic, fisheries-independent data collection in UK and European waters.