Efficacy of baited remote underwater video systems and bait type in the cool-temperature zone for monitoring 'no-take' marine reserves

Cool-temperate reef fish assemblages are often poorly described below 20 m because of depth limitations of conventional diver-based visual census. The recent development of baited remote underwater video systems (BRUVs) provide an alternative quantitative sampling method. Despite being used in warmer temperate and tropical waters and cool-temperate waters in Victoria, initial trials of vertical BRUVs in Tasmania, Australia, provided poor results. Our study explored possible reasons for this, including using horizontal BRUVs and various baits across a depth gradient. We examined the fish fauna in, and adjacent to, a small, but long-established, no-take marine reserve to assess the potential for BRUVs to enhance monitoring programs in exposed coastal environments. Significant differences in the fish assemblage were described relating to location, depth and bait type, with pilchards being an effective bait type. Fish abundance and species richness increased with depth. The research validated BRUVs for monitoring deep-reef systems in Tasmania, reinforced the importance of depth in structuring fish assemblages and identified the range of observable species in this region that may not be fully captured with diver-based surveys alone. Power analyses were conducted using the data generated here to inform the amount of replication needed to detect biologically meaningful differences in targeted fish assemblages in subsequent studies examining the response of no-take marine reserves to protection. This facilitates future assessments of the effectiveness of Tasmanian no-take reserves and allows for more broad-scale studies that can address a range of ecological and conservation questions.