Grey and whitetip reef sharks on the Great Barrier Reef are in the midst of a catastrophic decline, according to researchers.
Credit: istockphoto
SYDNEY: Reef shark populations on the Great Barrier Reef are in the midst of a catastrophic collapse, according to a new Australian study.
"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 lead author William Robbins, of James Cook University in Townsville.
According to the team, reporting in this week's Current Biology, grey reef shark numbers have already declined to around three per cent of unfished levels and are currently declining so fast that they could collapse to one thousandth of their unfished levels within 20 years if current conditions continue.
Whitetip reef sharks fared little better: their numbers have already fallen to 20 per cent of unfished levels, and are headed towards five per cent within two decades.
"Our research indicates that current reef shark abundances and levels of fishing pressure are simply not sustainable," said Robbins. "It also suggests that immediate and substantial reductions in fishing pressure will be needed to give threatened populations any chance of recovery."
To arrive at their findings, the team conducted underwater counts of shark numbers and combined these data with mathematical models that project future population trends based on information about reef sharks' current survival, growth and reproductive rates.
The researchers also compared shark numbers 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 been effective at conserving reef sharks, while 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.
"Reef sharks mature late in life, and, like many whales and dolphins, produce very few offspring," notes co-author Mizue Hisano. "This makes it hard for them to bounce back from even low levels of fishing, such as poaching in green zones.
The recent re-zoning of the Great Barrier Reef, with its increased emphasis on building support for no-take zones among reef users, is an important step, says Sean Connolly, another of the study's authors.
"However, these efforts need to be combined with realistic limits on shark fishing for the ecosystem as a whole. Because shark fishing is intensifying, the population collapses that we have identified are likely to accelerate if we do not take action now."
It was especially disturbing that a collapse in shark populations had occurred on Australia's Great Barrier Reef, says Hisano. "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."
with the Australian Research Council
Saving sharks
We should stop killing these sea animals just for food and to fish they should have a life to. What if you were a shark or a fish fighting for your life like these in dangered animals? what did these poor animals do to you? They are just killing people and animals because thier lives are worst than humans because of us.
Once i read this book about sharks nature and it says that boots, makeup and some other stuff you dont want to use agin like AVON soap and leather boots. What you eat out of fish is a part of sharks. What part you are eatting is the sharks family just a little. Sharks are just afriad of people because aroun 10 years ago people were killing sharks just for fun but why they guard their home is because it is their property and somany people were trespassing by swimming and fishing and sea boatting. Ya soometimes its kind of fun to some people once they first killed a shark because they know that they would do it much more. They would tell their friends and they would tell thier friends and people would love or like to kill sharks. Sharks dont want to die just like we dont want to die like them.
Sharks
Did you know that sharks, through their food up in the air, before they eat their pray.Also sharks are, one of the top animals around the reith. When sharks are around food, other animals come to get that food that the sharks want,the sharks say hay this is my teretory,this is were my food is so back OFF pal.