Auckland University scientists are calling for an expansion of the Cape Rodney-Okakari Point (Goat Island) Marine Reserve, to stop crayfish numbers dwindling to an all-time low.

The university operates the Leigh Marine Laboratory, and the reserve was originally set up for scientific research purposes in 1975.

It is administered by the Department of Conservation.

Laboratory senior lecturer Dr Nick Shears says the first research into crayfish numbers, when the reserve opened, showed there were 10 per 500 square metres.

As the 518ha reserve became more effective that figure grew to around 40, but due to more intensive fishing on the reserve border, numbers have dropped back to just 10 – wiping out more than 40 years of conservation efforts.

'The reserve boundary extends 800 metres offshore, but the sand flats where the crayfish feed are beyond this,” says Nick.

'The reserve needs to constantly protect its marine life, which isn't happening, and this means we could soon have less crayfish than when the reserve first opened.”

Relevant agencies are aware of the issue and a Sea Change Plan, designed to enhance the Hauraki Gulf, proposes to extend the boundary a further 2.2km to 3km.

However, no time frames have been set for when the proposal might come into effect. In August, the university approached the Auckland Conservation Board with its concerns.

Board chair Lyn Mayes shares the university's concern.

'The board supports the call by researchers to extend the boundary of the reserve to a minimum of 3km offshore.”

But she says the board can't comment on any action it may have taken to try and get the boundary extended.

Rodney MP Mark Mitchell says he will be right behind any proposal to expand the reserve.

'I'm a huge fan of marine reserves and I can't see any downsides to expanding the one at Goat Island,” Mr Mitchell says.

'It serves our researchers, is a good learning facility and a great tourist attraction.”

Leigh resident and honorary Department of Conservation ranger Tony Enderby says he supports a boundary expansion, but has concerns about opposition.

'It's a great idea, but I have doubts it will happen because a lot of fishermen are opposed to the idea,” he says.

Minister for Conservation Eugenie Sage says she can't comment on the specific proposal to expand the reserve, but says government agencies are working out the best way to progress the Sea Change Plan proposals.

Meanwhile, marine life in local reserves is having to face the additional challenge of sea pollution.

Earlier this month, Goat Island Dive and Snorkel owners Stone and Tine Meharry-Roland found a set net drifting near the Tawharanui reserve full of dead fish.

'People set these nets and then don't monitor them closely. They drift off and catch all sorts of marine life that gets in their way,” Mr Meharry-Roland says.

'The nets are often made of nylon so can easily last 30 years in the water.”

The pair regularly do clean-ups around the coastline and find a lot of rubbish.

'We pick up everything from tyres to fridges, bikes, crayfish pots and, most commonly, plastic waste.”

Goat Island sees around 350,000 visitors each summer and Stone says beachgoers and anglers all need to be mindful of rubbish and the damage it does.