Source: Zee News

12/07/06 

WASHINGTON, DC - A new study by Australian scientists has revealed that overfishing is threatening the existence of coral reef sharks in Australia`s Great Barrier Reef.

The research by William Robbins and colleagues at James Cook University and the ARC Centre of Excellence for Coral Reef Studies, found that grey reef shark numbers had already declined to around three percent of unfished levels, and had the possibility of collapsing to one thousandth of their levels within the next 20 years if present conditions continue.

According to the study "Ongoing collapse of coral reef shark populations", Whitetip reef sharks fared little better: at 20 percent of unfished levels, heading towards the five percent mark within two decades.

Lead author Robbins said the study was the first of its kind to combine direct underwater counts of shark abundance with mathematical models and 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 Robbins.

"It also suggests that immediate and substantial reductions in fishing pressure will be needed to give threatened populations any chance of recovery," he added.

In their study, 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, are 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," he said.

"Reef sharks mature late in life, and, like many whales and dolphins, produce very few offspring. This makes it hard for them to bounce back from even low levels of fishing, such as poaching in green zones," added Mizue Hisano, a co-author of the study.

"It is especially disturbing that a collapse in shark populations has occurred on Australia`s Great Barrier Reef. The Great Barrier Reef is widely regarded as one of the world`s best-managed reef ecosystems. This means the situation may well be even more serious on reefs elsewhere in the world," Hisano said.

The study appears in this week`s issue of Current Biology.