Widespread diversity deficits of coral reef sharks and rays

A global survey of coral reefs reveals that overfishing is driving resident shark species toward extinction, causing diversity deficits in reef elasmobranch (shark and ray) assemblages. Our species-level analysis revealed global declines of 60 to 73% for five common resident reef shark species and that individual shark species were not detected at 34 to 47% of surveyed reefs. As reefs become more shark-depleted, rays begin to dominate assemblages. Shark-dominated assemblages persist in wealthy nations with strong governance and in highly protected areas, whereas poverty, weak governance, and a lack of shark management are associated with depauperate assemblages mainly composed of rays. Without action to address these diversity deficits, loss of ecological function and ecosystem services will increasingly affect human communities., General BRUVS methods
FinPrint sampling of coral reefs used Baited Underwater Video Stations (BRUVS). BRUVS consisted of a weighted metal frame holding a compact high-resolution video camera (typically a GoPro) and a 1 m arm holding a bait bag containing 1 kg of crushed oily fish in front of the camera. Where possible, at least 50 BRUVS were deployed at a reef (defined as a single isolated reef, or a patch of a large reef ~10 km2). Four to eight BRUVS were deployed simultaneously at a reef, with all BRUVS set at least 500 m from each other. BRUVS were deployed between 0-40 m depth and for a minimum of 60 minutes. This deployment time was sufficient to adequately sample the core coral reef shark and ray species. At each BRUVS drop, the date, depth, time of deployment and retrieval, GPS coordinates, sea conditions, and weather conditions were collected.
All videos were read by trained annotators using either Event Measure (https://www.seagis.com.au/event.html) or FinPrint Annotator (https..., R code for the analysis in this paper is provided. All data files used in the analysis are also provided. It will be necessary to specify the location of the data files in the R code to enable it to run. README.txt file contains additional information.