BRUV’s consist of a video camera (GoPro Hero 3) inside an underwater housing that is mounted on an aluminium frame (fig 2). Bait is placed in a wire cage mounted on a pole in the camera’s field of view. 1 kg of oily bait is used as standardized bait for every single BRUV drop. BRUV sampling is conducted throughout the Matra Marine Natural Recreation Park surrounding the three islands of Gili Trawangan, Gili Meno, and Gili Air in both recognized dive locations and exploratory areas on the perimeter of the MPA. Locations of deployment for each site are chosen using a random number generator to avoid location bias. BRUVs are placed on the random location at daylight hours and, upon arrival, the vessel captain is asked to find the closest suitable location for deployment.
The deployments are typically done in an area between 4m and 30m of depth, with a flat bottom to maximize line of sight, and at least 10 m away from an edge to prevent from loosing the BRUV due to strong current. BRUV’s are deployed using SCUBA gear and diving lift bags to guide it away from live coral and to orient the BRUV facing down current. The BRUV is in the water for over 90 minutes and other activities (e.g training dives or survey dives) are simultaneously conducted no closer than 500m from the BRUV drop site. At both the start and the end of each deployment environmental variable are measured including, water current speed (with a General Oceanics, Mechanical Flowmeter), bottom depth, underwater visibility and water temperature. BRUVs are dropped 4 times a week until a minimum of 200 drops throughout the MPA area is reached. Each video is viewed twice by a trained volunteer on a computer and data is recorded. Every elasmobranch or commercially valuable fish species present in the frame is counted and recorded.