Since becoming New Zealand's first marine reserve in 1975, Goat Island has proven to be worth its weight in gold - and snapper.

The 518ha area at Leigh, officially known as Cape Rodney-Okakari Point Marine Reserve, has provided scientific researchers, snorkellers and divers with a thriving marine ecosystem to observe. It's also played a major role in helping restore balance to the waters around it, through its large stocks of snapper and crayfish and replenished kelp forests.

"It shows what can change if we leave areas of the sea alone," says Tom Trnski, head of natural sciences at Auckland Museum.

Before Goat Island became a no-take zone, kina had left barrens - rocks scoured clean of all life, especially seaweed. "Now these seaweeds are apartment blocks for many different species - there's incredible diversity," Trnski says. "Snapper and crayfish are thriving. Fatter, older and larger snapper produce many more eggs. Our reserves supply eggs and larvae to the waters around them, making a much greater contribution than fish from outside the reserve."

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Goat Island is one of five marine reserves within the Hauraki Gulf Marine Park, stretching over 1.2m ha, but only 0.3 per cent of the gulf is protected from fishing.

Reports on the "State of Our Gulf" over the past five years have been murky. Snapper populations are just 19 per cent of stocks before human fishing - well below the 40 per cent aimed for to sustain future generations. Increased bottom trawling has distressed the habitat that juvenile fish like snapper need to survive.

Tom Trnski on the beach. Photo / Rachael Sagar.
Tom Trnski on the beach. Photo / Rachael Sagar.

The state of the seafloor has changed dramatically - muddy sediment has built up as Auckland has become more populated in the past 175 years. Clearing land for houses, heavy metals from industry, forestry erosion and fertiliser run-off from farms have all contributed to the Gulf's poor health.

Destructive invasive species such as the Mediterranean fanworm are also threatening Auckland's waters; four introduced species have been found since 2011. The 55-strong population of bryde's whales living in the Gulf are too often killed by ship strike. The shipping industry is working towards ships sailing through the Gulf at around 10 knots, reducing the chance of a fatal strike.

New Zealand's first marine spatial plan - due to be released later this year - should help to restore the Gulf's once vibrant ecosystems by making recommendations on how to best manage the waterways.

Discussions on the plan, known as Sea Change - Tai Timu Tai Pari, has brought together the region's councils, government agencies, iwi, fishing operators, farmers, scientists and the wider community.

"If we want to look after the Hauraki Gulf we need to restore some of the old dynamic and limit the impact humans are having on the marine environment. It's never too late," Trnski says. "Water in the marine environment is always moving, so it's really good at recovering.

"If you look after an area it will recover by itself, as reserves like Goat Island, Long Bay and now Tawharanui [a marine reserve since 2011] are showing. Other places need to be given that opportunity."

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