With a grunt and a splash, the baited remote underwater video system (or BRUVs, as it is more commonly known) slowly sinks from the frothy ocean surface to the calmer waters below. It’s a little green down here, but the visibility is stellar even though all we can see right now is silent habitat since any nearby fish have scattered thanks to all the commotion. But they’ll be back, curiosity getting the better of them. And that’s perfect because it’ll allow the stand-out scientific tool to do her job: observe.
Consisting of a steel frame and two video cameras inside waterproof housings, BRUVs are a common fish-surveying tool around the world. These stationary, seafloor camera stations use bait to attract fish in their vicinity, recording the species attracted to the bait or swimming past the camera lens. Excellent for observing marine life in hard-to-reach habitats, the Wildlife Conservation Society (WCS) and the Instituto Oceanográfico de Moçambique (InOM) have been using them to assess sharks and rays off southern Mozambique. Conducted by scientists Dave van Beuningen (WCS), Jorge Sitoe (WCS), Emildo Notisso (InOM) and Jonas Chambo (Ocean Revolution Mozambique), this research is part of a broader initiative that uses BRUVs technology to identify shark and ray hotspots throughout the southwest Indian Ocean.
The Mozambican coastline is one considered by many to be one of the most important shark hotspots in the world even though little is known about the elasmobranchs that roam this area. With approximately 147 shark and ray species recorded in Mozambique, it’s not uncommon to see one attracted to these underwater camera systems, often getting so close all the camera sees is their ampullae of Lorenzini under their snouts (dark mucus-filled pores that are able to detect electric fields). Not only do the BRUVs allow researchers the ability to identify individual fish species that enter the camera’s field of view, the stereo video cameras have their fields of view calibrated, allowing accurate estimates of the size of any animal passing by. Big or small, the scientists are hunched over the computer for hours trying to make sure they capture every fish and get the best shot to accurately measure each species.
So imagine their surprise when a flash of grey-and-white obscures the camera. The great white shark (Carcharodon carcharias) is notorious off African waters, although it has become rarer in some countries and locales thanks to orcas. Found in cool, coastal waters around the world, these torpedo-shaped predators have been captured on BRUV footage before. Often the camera or bait bag gets bit, dragged and thrashed around until the shark either tires or rips its prize off and gulps it down. But this shark was unique – his distinct facial scars and caudal fin coloration matched that of a shark that had been tagged in South Africa and later recorded in a a BRUV survey off Struisbaai in May 2022.
The researchers slowed down the footage to see if a tag was visible… and… wait… yup! There it was! The position confirms it was the same individual shark, a juvenile male. “This single observation is of great value to shark science and conservation, as it confirms a transboundary movement, on the scale of thousands of kilometers, of a threatened shark species, which has major implications for the management of this species,” says Rhett Bennett, PI on the BRUV survey project in Mozambique. “The individual ID match also highlights yet another value of BRUVs, and specifically video records, as useful research tools for shark and ray science.”
While the BRUV surveys are led by WCS and InOM, in collaboration with Ocean Revolution and the South African Institute for Aquatic Biodiversity, the white shark tagging in South Africa is part of a PhD project led by marine biologist Alison Towner of Rhodes University. The BRUV surveys in South Africa were conducted in collaboration with Hazmat Productions and Discovery Channel. Says Towner of the observation: “This important ID match and confirmation of transboundary movement has come at a time that the Southern African white shark population is facing the additional threat of orca predation on top of other anthropogenic threats such as shark nets. It’s a great example of collaboration between different research platforms.”
Not only are great white shark populations suffering in South Africa, all sharks in general aren’t doing too well. The most recent global IUCN Red List of Threatened Species assessment of sharks estimated that over one third of species (37%) are threatened with extinction (i.e. considered Critically Endangered, Endangered, or Vulnerable). Under immense pressure globally from fisheries, the findings will help to inform fisheries and resource managers in South Africa and Mozambique about the migratory capacity of white sharks, and the need for multilateral or at least bilateral management measures for this and other threatened shark and ray species that are moving between the waters of these countries.
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