Optimal BRUVs (baited remote underwater video system) survey design for reef fish monitoring in the Stilbaai Marine Protected Area

Abstract

Marine protected areas (MPAs) play an important role in coastal conservation, but there is presently no uniformly applied methodology for monitoring the efficacy of coastal fish protection. Whereas underwater visual census and controlled angling surveys have been used, their skilled-labour requirements and environmental impact have prevented their nation-wide application in South Africa. We used a baited remote underwater video system (BRUVs) to provide the first survey of reef fishes in the Stilbaai MPA (SMPA), and assessed the deployment time and sample size requirements of BRUVs for reef fish monitoring. Thirty-eight species, including 13 chondrichthyans, were recorded in one-hour deployments across 29 sites in the 11.3 km² no-take zone of the SMPA, in depths ranging from 5 to 41 m. Bait was limited to sardine Sardinops sagax homogenate, but the species recorded by BRUVs comprised several feeding guilds, including herbivores. Optimal deployment time was 49 min, but 60 min is recommended as a conservative and practical standard. Over a five-year period, annual BRUVs sample sizes required to detect increases in abundance of 0.1 y⁻¹ with 80% power would be 28 deployments for abundant species and 129 for rare species. Detection of decreases of equivalent magnitude will require more samples.

Keywords:

• BRUVs
• power analysis
• reef fish survey