Baited remote underwater videos

Nurse shark relative abundance was surveyed using Baited Remote Underwater Videos (BRUVs). BRUVs have been previously found to produce comparable estimates of abundance to those obtained from underwater visual census and baited hook and line methods [40,41], and to be well suited to sampling generalist and large carnivores [42]. BRUVs consisted of a GoPro camera mounted on a metal frame, with a wire mesh bag of crushed baitfish suspended 110cm in front of the GoPro. A 30cm long metal bar was fixed perpendicularly above the bait, to allow length estimations of nurse sharks to be made (see [41] for more information on BRUVs). BRUVs were deployed from a boat using a rope and in-water operators guided it away from live coral. Each BRUV was left to record continuously for at least 65 minutes after settling on the sea floor and manually retrieved afterwards using a small marker float attached to the rope used to lower the BRUV into position. Time of deployment, GPS location, bottom depth, type of bait used, habitat type (forereef, backreef, patchreef, or seagrass beds), and positioning within or outside MPA borders were recorded for each BRUV deployment. BRUVs were deployed at study regions from 2012 to 2016 (Table 1). A total of 409 successful BRUV deployments were made during the course of the surveys across all regions. BRUV deployments were equally distributed within and outside protected areas (204 and 205 deployments, respectively); 245 BRUVS were deployed in reef ecosystems and 164 in lagoon ecosystems.

Summary statistics of nurse shark (Ginglymostoma cirratum) surveys, including: Area estimation, BRUV (Baited Remote Underwater Video) deployments, and transect surveys for all study regions (GLO = Glovers Reef; LRA = Lighthouse Reef Atoll; NBZ = Northern Belize; SBZ = Southern Belize; TUR = Turneffe Atoll). MPA = Marine Protected Areas; Positive refers to the count of BRUVs or transects in which a nurse shark was sighted; FO = Frequency of Occurrence, expressed as the number of positive BRUVs over the number of BRUVs deployed; ER = Encounter Rate, expressed as sharks per km².