Baited Remote Underwater Video (BRUV) around the Gili Islands – Gili Matra Marine Park

Introduction

Due to the difficulties of studying elasmobranch abundance in the wild, different techniques had to be invented in order to address different ecological questions. One of these techniques is the Baited Remote Underwater Video (BRUV). This shark study method has been used in numerous studies around the world and has been shown very successful.

Objectives

The BRUV project is part of a collection of researchers from Florida International University (FIU) to estimate and compare the relative abundance of predator fish species, including sharks and rays, inside and outside marine protected areas (MPAs). These species are also the most commercially valuable and play and important role in the local villages everyday life. Several questions are waiting for an answer through this study: Is the correlation between diversity and relative abundance of elasmobranchs, and the size of the MPA? Are the MPAs created by NGOs and local villages being successful? Many people in the Gilis are not aware that the entire area is a protected marine park called Gili Matra Marine Natural Recreation Park.

Gili-Shark-Conservation-Gili-Islands-Gili-Matara-Marine-Park

Methodology

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.