Australia's government is on the rocks, struggling in political polls.

So it took a brave minister to hold a press conference in front of circling sharks.

Tony Burke, the environment minister, used Sydney Aquarium as a backdrop to launch what he says is the world’s most ambitious network of protected marine parks.

This includes an area of ocean larger in size than India - 3.3 million square kilometres.

But that, Australia's government hopes, will be just the beginning.

They want their protection zones to become models for other countries around the world. As the minister told me: “Hopefully this does set a very strong benchmark for the rest of the world on protection for that great shared resource which is our ocean.”

The timing of Australia's announcement is no accident. In a week the Rio+20 conference on sustainable development begins.

Australia wants to brandish its credentials as an environmental trend-setter. Its carbon tax begins in less than a month: that too could be a benchmark scheme for the world.

But Australia's government is green only up to a point.

On the carbon tax, compensation for the big polluters is too generous, say pressure groups.

On marine parks, commercial fishermen complain that while they will be hit hard, oil and gas companies – worth more in royalties – have been let off lightly.

They've largely been successful in their lobbying to keep their key areas of interest outside the most protected zones. The big bucks those industries create gives them clout.

As if to underline that point, earlier this month Australia was criticised by UNESCO for the rapid development of land adjacent to the Great Barrier Reef: huge processing plants from which to ship Liquefied Natural Gas are being built in Gladstone Harbour. Boats much bigger than buildings are allowed to carry coal through protected waters.

Nevertheless, Green groups in Australia are pleased with their government's marine park plans.

I could have sworn that even some of the sharks were smiling this morning – they were certainly baring their teeth. Although they may have just been contemplating lunch.