Underwater Sharks

Coral reef shark populations on the Great Barrier Reef are in the midst of a catastrophic collapse, a new study suggests.

Researchers found that grey reef shark numbers are currently declining so fast that they could collapse to one thousandth of their un-fished levels within 20 years if current conditions continue.  

The study is the first of its kind to combine direct underwater counts of shark abundance with mathematical models that project future population trends based on information about reef sharks' current survival, growth and reproductive rates.

"Our research indicates that current reef shark abundances and levels of fishing pressure are simply not sustainable.  Reef sharks are effectively on a fast track to 'ecological extinction' - becoming so rare that they will no longer play their part in the ecology and food web of the reef," said study lead author, William Robbins from the James Cook University.

The researchers also compared shark abundances in reefs that had been zoned for different levels of fishing in the decades preceding the study.  They found that some types of no-take zones had worked very effectively for reef sharks, but that others had not. 

In particular, reef shark abundances in "pink zones", which are strictly policed no-take zones that require special permits to enter, were as large as on oceanic reefs with virtually no shark fishing.  In contrast, shark abundances in "green zones", where illegal fishing is much harder to prevent, were similar to abundances in legally fishable areas.

The study appears in this week's issue of the journal Current Biology.

---LiveScience Staff

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