One hundred and sixty-five species of elasmobranchs (sharks and rays) have been recorded off the Brazilian coast, accounting for 55% of the endangered Brazilian marine ichthyofauna. With 54 species classified in the IUCN threat categories (Vulnerable, Endangered or Critically Endangered), it is imperative for scientists to assess population trends and conservation statuses of the species here. But, like many elasmobranchs, researchers lack crucial population data to make informed decisions to pave the wave for sustainable management of these animals.
Enter the baited remote underwater stereo-video system (stereo-BRUVs). BRUVs consist of a video camera (usually a GoPro) inside an underwater housing that is mounted on an aluminium frame and has a treat bag full of bait to entince animals to come into the camera’s frame. These underwater video stations are a common worldwide fish-surveying tool due to the availability of this low-cost technological set up. Widely adopted as a non-extractive technique, a team of researchers deployed BRUVs at the Brazilian oceanic islands of the Trindade and Martin Vaz Archipelago (TMV) and Saint Peter and Saint Paul Archipelago (SPSPA).
The Trindade and Martin Vaz Archipelago is highly isolated, located some 746 miles (about 1200 kilometers) off the Brazilian coast and is the most eastward point of the Brazilian territory. A result of volcanic activity deep below the Atlantic Ocean, it has a tropical oceanic climate. Fourteen of the 60 deployments recorded 19 sharks in Trindade Island, including two tiger sharks (Galeocerdo cuvier), 11 Caribbean reef sharks (Carcharhinus perezi), two nurse sharks (Ginglymostoma cirratum), and three scalloped hammerhead sharks (Sphyrna lewini).
The Saint Peter and Saint Paul Archipelago is a group of small islets and rocks in the Atlantic Ocean, lying close to the equator and close to the Intertropical Convergence Zone (ITCZ), an area of constant and severe thunderstorms. This archipelago has been a designated multiple-use marine protected area (MPA) since 1986, especially dedicated to the protection and maintenance of the region’s biodiversity. In the SPSPA, only two of five pelagic deployments recorded sharks – two silky sharks (Carcharhinus falciformis) in each deployment, and two of 14 demersal deployments recorded one silky shark and one Galapagos shark (Carcharhinus galapagensis).
Despite its name, the Galapagos shark is not endemic to the Galapagos Marine Reserve and is found all over the world. A species of requiem shark – a family of migratory, live-bearing sharks found in warm waters – they were regarded as locally extinct in the SPSPA so spotting them on the BRUV footage was very exciting for the scientists. This evidence has also sparked many questions, leading the researchers to wonder how many more of these individuals swim in the SPSPA waters.
According to the article, systematic fish and shark studies using other non-invasive methods (such as underwater visual census and remotely operated vehicles) in these two Brazilian oceanic islands have not recorded sharks in recent decades. The hope is that this evidence can allow for further non-invasive research in the area and perhaps continue to unravel the oceanic secrets here.