Marine reserves that protect the entire reef ecosystem are more likely to sustain healthy shark populations than single species ‘shark sanctuaries’ or zoned schemes that only fully protect a few reefs within an area, according to an international study led by The University of Western Australia.
The study, published today in the journal PLOS ONE, was carried out by researchers from UWA’s School of Biological Sciences’ Marine Futures group and ZSL (Zoological Society of London).
Baited video systems, called BRUVS, were used to survey shark and fish numbers across different habitats and depth zones of the reefs of the British Indian Ocean Territory Marine Reserve (BMR) in the central Indian Ocean.
Declared in April 2010, the BMR is one of the world’s largest no-take marine reserves, containing an isolated archipelago of reefs extending more than 300km north to south and 200km east to west, making it one of the best places in the world to study reef systems in their natural state.
The researchers found that reef shark abundance was most strongly linked to the amount of prey fish in an area rather than the quality of the reef habitat itself, suggesting that overall, sharks respond most strongly to food availability.
Lead author David Tickler, from UWA’s School of Biological Sciences, said individual shark species tended to vary in their habitat preferences.
“We found that shallow reef sites were important for common species such as white tip and grey reef sharks, whereas deep reefs on submerged seamounts were the haunt of hammerhead and silvertip sharks and isolated banks were important to juveniles,” Mr Tickler said.
“To maintain both abundance and diversity of reef sharks, we need to make sure that their food is protected and that a range of habitats are included. This is why a large no-take marine reserve, such as the BMR, is important to shark conservation.
“Reef systems are a complex interlocking web of predator and prey relationships; disturbing one element of that system has knock-on effects throughout the reef, and conservation goals are best achieved when all parts – predators, prey and habitat – are protected.”
Co-author Dr Tom Letessier from ZSL said no-take reserves such as the BMR, located far from humans, were home to a remarkable number and diversity of sharks.
“This study shows that at the local scale within the reserve, shark abundance is intimately linked to their prey (fish) and their habitats. Our work is evidence of the importance of protecting the entire ecosystem: effective shark conservation measures must include protection of shark prey and their habitats.”
Co-author Professor Jessica Meeuwig said the study, partly funded by the Bertarelli Foundation, had broad significance for marine conservation.
“Sharks are fundamental to healthy ecosystems and the threat they face from indiscriminate fishing is clear,” Professor Meeuwig said.
“Like the predators of the African plains, sharks dominate the marine ecosystems of the ‘Blue Serengeti’ and provide valuable ecosystem services as well as direct benefits to industries such as dive tourism. The demand for shark meat and fins has led to declines of up to 90 per cent in some species, and fully protected marine reserves are a vital tool to help rebuild their populations.”
David Tickler (UWA School of Biological Sciences) (+61 4) 51 00 87 55
David Stacey (UWA Media and PR Manager) (+61 8) 6488 3229 / (+61 4) 32 637 716