A team of scientists from Australia and Canada monitored the health of reefs 300 kilometres off the Australian coast – an area where Indonesian fishermen have been catching sharks for centuries. They found that in areas where shark numbers were reduced, the entire food chain of the reef was affected.
‘We saw increasing numbers of mid-level predators – such as snappers – and a reduction in the number of herbivores such as parrotfishes,’ said Mark Meekan from the Australian Institute of Marine Science, who led the study. ‘The parrotfishes are very important to coral reef health because they eat the algae that would otherwise overwhelm young corals on reefs recovering from natural disturbances.’
Previous tracking studies have shown that individual reef sharks often remain close to a particular coral reef, so even relatively small marine protected areas could help to relieve some anthropogenic effects on reefs, including pollution damage and coral bleaching.
‘The reefs provided us with a unique opportunity to isolate the impact of overfishing of sharks on reef resilience, and assess that impact in the broader context of climate change pressures threatening coral reefs,’ said Jonathan Ruppert of the University of Toronto. ‘Shark fishing appears to have quite dramatic effects on coral reef ecosystems. Given that sharks are in decline on reefs worldwide, largely due to the shark fin trade, this information may prove integral to restoration and conservation efforts.’
This story was published in the November 2013 edition of Geographical Magazine