Study suggests overfishing of sharks is harming coral reefs

September 18, 2013
This image shows divers photographing reef sharks. Credit: Peter Verhoog of the Dutch Shark Society

A team of scientists from Canada and Australia have discovered that the decline in shark populations is detrimental to coral reefs.

"Where shark numbers are reduced due to , there is also a decrease in the herbivorous fishes which play a key role in promoting reef health," said Jonathan Ruppert, a recent University of Toronto PhD graduate. Ruppert was part of a team engaged in long-term monitoring of reefs off Australians northwest coast.

Team leader Mark Meekan of the Australian Institute of Marine Science (AIMS), said that the results might, at first glance, seem strange. "However our analysis suggests that where shark numbers are reduced, we see a fundamental change in the structure of on reefs."

"We saw increasing numbers of mid-level predators—such as snappers—and a reduction in the number of herbivores such as parrotfishes. 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," said Meekan.

According to Ruppert, the study comes at an opportune time—coral reefs are facing a number of pressures both from direct human activity, such as over-fishing, as well as from climate change.

This is an image of reef sharks. Credit: Peter Verhoog of the Dutch Shark Society

The reefs studied are about 300 kilometres off the coast of northwest Australia where Indonesian fishers target —a practice stretching back several centuries and which continues under an Australian-Indonesian memorandum of understanding.

"The reefs provided us with a unique opportunity to isolate the impact of over-fishing of sharks on reef resilience, and assess that impact in the broader context of climate change pressures threatening coral reefs," said Ruppert. "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 is an image of a reef shark. Credit: Peter Verhoog of the Dutch Shark Society

Tracking studies show that, in many cases, individual reef sharks are closely attached to certain coral reefs. This means that even relatively small marine-protected areas could be effective in protecting the top-level predators and allowing to better able to recover from coral bleaching or large cyclones which are increasing in frequency due to the warming of the oceans as a result of .

The study will appear in the September 28 issue of journal PLOS ONE.

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1 / 5 (12) Sep 19, 2013
Very interesting and insightful study. I am sure despite the evidence though, sharks will continue to be hunted down and killed for shark fin soup.

A shame about the ending paragraph with the climate change bullshit though.

Kind of like when they thought AGW was wiping out frogs, for 10 years later, actual scientists, using controls and proper experiments found out it was a virus killing them off.

Oh and the same kind of thing with many species.

It's usually blanketed with the easy answer of AGW, and then actual scientists come along and do some actual science to find the actual answer.

I'm not suggesting shark hunting is the sole cause of coral decline btw.
1 / 5 (10) Sep 19, 2013
There is a recent TED talk about a similar situation that happened with wolves in Yellowstone National Park where the apex predator keeps the ecosystem health. I would recommend it for anyone that is interested.

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