Title
Informing improved conservation and management of elasmobranchs in the Western Indian Ocean: Insights from baited remote underwater video surveys
Author(s)
Dave van Beuningen; Rhett Bennett; Anthony Bernard; Jorge Sitoe; Mike Markovina; Stela Fernando; Naseeba Sidat; Remy Oddenyo; Roxanne Juby; Aseeqah Davids; Katie Heckendorn; Isabel da Silva
Published
2022
Abstract
Elasmobranchs in the Western Indian Ocean (WIO) are heavily overexploited, with 41% of the 215 known species considered threatened with extinction. Limited information and increasing fishery threats call for the improved conservation and management of elasmobranchs in this region. We conducted ecological surveys using stereo baited remote underwater video (stereo-BRUV), to provide data on elasmobranch distribution ranges, diversity, relative abundance and habitat associations. Over 1900 hour-long BRUV deployments were conducted over reef and sand habitats (5–98 m deep) across Comoros, Kenya, Madagascar, Mozambique, South Africa and Tanzania, from November 2016 to March 2022. The surveys revealed inter alia a hotspot for the Critically Endangered whitespotted wedgefish Rhynchobatus djiddensis, a 2000-km range extension of the Critically Endangered shorttail nurse shark Pseudoginglymostoma brevicaudatum, and the importance of sand habitats for elasmobranchs. Overall, South Africa and southern Mozambique displayed the highest frequency of occurrence (52% and 40% of samples with at least one elasmobranch recorded, respectively) and species richness (21 and 16 species, respectively), supporting this area’s recognition as a global elasmobranch hotspot. However, frequency of occurrence overall was generally much lower than results from other regions globally. Notably, zero sharks were recorded in 165 deployments throughout Kenya, and 120 deployments in Antongil Bay in northeast Madagascar, the only designated shark sanctuary in the WIO. These findings confirm the incredible impacts of coastal fisheries on elasmobranchs in the WIO; they will help to inform area-based management measures and identify areas for focused conservation efforts for elasmobranchs in this region.
Keywords
elasmobranch; conservation; management; BRUV

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