Fisheries on the verge of collapse and sediment-choked and polluted waterways have been laid bare in a new report on the ailing health of Auckland and Waikato's big blue backyard.
And authors of the State of the Gulf 2020 warn little improvements have been made since the Hauraki Gulf Marine Park was established 20 years ago, with population growth, coastal developments and climate change all pointing towards an even more dire future without drastic action.
The report, prepared by the Hauraki Gulf Forum, asks whether legislation set up to protect the 1.2-million-hectare Park needs to be revisited, and argue the balance is tipped too far towards "development and utilisation" over the environment.
Since human arrival there have been dramatic changes to the Gulf – known to Māori as Tīkapa Moana – with decades of destructive fishing methods not only depleting fishing biomass today to less than half the level in 1925, but decimating the seabed, leaving vast sections wastelands.
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Trevally numbers have plummeted by 86 per cent from historic levels, snapper by 83 per cent, sharks - a key part of the ecosystem - by 86 per cent and dolphins 97 per cent.
Forest clearance, development and farming on land has seen sediment muddy the once-crystal clear waters, leaving the previously sandy beaches layered in sludge, and shellfish-laden reefs choked in silt.
Dredging has stripped the seafloor of all its mussel beds - crucial for filtering the water, reduced scallops to alarmingly low levels, and crayfish/kōura are now regarded "functionally extinct".
The report highlights the interrelatedness of the various species, with the decline of crayfish and snapper leading to the march of the "kina barren".
Kina – preyed on by crayfish and snapper – eat kelp and other algae, and when they are released from predation they multiply and can strip the kelp forests to bare rock, depriving a diverse range of other kelp-dwelling species of a habitat, leaving a desert of malnourished, nutrient-depleted kina.
Despite changes to recreational bag and size limits seeing some improvements for snapper, the authors warn it may not be enough to stop the "proliferation of kina barrens".
Commercial fishing has increased, though a ban on trawling in the inner parts of the Gulf has seen the practice drop over 50 per cent since 2000.
Danish Seine nets meanwhile have continued unabated, and between 2016–17 and 2018–19 about 22 of the nets were set in restricted areas.
The authors also expressed concern for seabirds, with the Hauraki Gulf a crucial habitat to over 20 per cent of the world's species, and shorebirds.
While seabird captures have reduced, the amount making the park, a world-renowned habitat, home classed as "threatened" had increased more than fivefold from 4 to 22 per cent since 2000.
Authors also railed against the lack of movement in increasing protected areas, with marine reserves only increasing by 0.05 per cent in 20 years, covering just 0.3 per cent of the Marine Park.
But it also offered glimmers of hope, noting the tide may slowly be turning with improved regulations reducing sediment and run-off in some areas, along with Government action on implementing the much-vaunted Sea Change Marine Spatial Plan.
Minister of Conservation Eugenie Sage has also expressed support for the Forum's goal of protecting at least 20 per cent of the park, with 10 per cent "no take" marine reserves.
Authors also highlighted the restoration of Gulf islands, with pest-free islands increasing from 25 in 2000 covering 1200ha to 40 now covering 10,000ha.
However, rapid growth that has seen Auckland's population increase 500,000 people in 20 years, an increase in coastal development sites and climate change impacts could see a reverse to many improvements, the authors wrote.
Moana Tamaariki-Pohe, deputy Forum chair at the time the report was being written, said the issues come down to "the struggle between economic development and population growth on the one hand, and environmental loss on the other".
She asked if it was time to consider if the Hauraki Gulf Marine Park Act – the only instrument advocating for the Gulf – was effective enough, and whether it had the balance between "environmental, economic and social values right".
"It doesn't appear to have the strength to turn things around."
The report will be publicly released this afternoon at Auckland's Royal New Zealand Yacht Squadron, attended by Minister of Conservation Eugenie Sage.
State of the Gulf 2020
The march of the "kina barren"
With kōura/crayfish classed as "functionally extinct" in many parts of the marine park and tāmure/snapper down 83 per cent on historic levels there has been a proliferation of "kina barrens" on subtidal reefs.
Kina in turn feed on kelp, removing a vital habitat for marine life.
The report warns current catch and bag limits might not be enough restore the balance to keep the ecosystem in check.
Sediment and water quality
Sediment is ranked the third highest threat to New Zealand's marine habitats, after ocean acidification and global warming. Land activities, such as forestry, farming, mining, draining of wetlands and urban development, have greatly increased the amount of sediment that enters our waterways and harbours.
Sedimentation rates in the Waikato over the past 100 years are around 100 times those of pre-human times. Despite council regulations containing sedimentation, high inputs are still occurring in some estuaries, which is reflected in the increasing proportion of mud and very fine sand at many of the monitored sites over the last 10 years, including sites in Kuranui Bay, Miranda, Okura, Mangemangeroa, Turanga and the Upper Waitematā.
There are also worrying signs that nutrient run-off from the Hauraki Plains is adversely affecting the Firth of Thames. Conversely, nutrient concentrations in Auckland's coastal waters are now lower than they were before the Marine Park was established, although the situation appears to be worsening again with concentrations of some key nutrients increasing on the Auckland coast over the past 10 years.
Since 2000, seabird species that breed in the Marine Park classed as "threatened" has increased fivefold to 22 per cent, and authors noted particular concern for the fairy tern, of which a maximum of 43 adults remain.
The number of seabirds captured by commercial fisheries had decreased by 54 per cent.
There was also concern for shorebird species, with three species "threatened" and two "at risk" in 2000, increasing to five and five respectively today.
Just 0.3 per cent of the Marine Park is protected as a marine reserve, with only a 0.05 per cent increase since 2000. The only new reserve to be created since the Marine Park was established is Te Matuku Marine Reserve, on the southern side of Waiheke Island. The application for that reserve was lodged before 2000.
In 2000 there were about 66 non-indigenous species in the Marine Park, but this had more than doubled to 144 by 2020. The number of marine pests had also increased from one - the Asian Date Mussel - to seven today, including the wakame, Mediterranean fan worm, Australian droplet tunicate, clubbed tunicate, Asian paddle crab and carpet sea squirt.
One of the positives seen in the Gulf's past 20 years has been the massive boost in biodiversity above water, due to the vast increase in predator-free islands.
In 2000 there were 25 such islands covering 1200ha, but this had since increased to 40 covering 10,000ha.
Increasing pressures on land
In 1999, Auckland's population of 1.2 million people was estimated to reach 2 million by 2050. By 2018 it was already at 1.7 million people. This rapid increase has seen a corresponding increase in coastal developments, and the number of marinas have also increased from 13 to 18.
Rubbish and plastic pollution continue to be major issues for the health of the Gulf, with charity group Sea Cleaners having removed over 8.8 million litres of rubbish from Auckland, Whangārei and Coromandel waterways since 2002.
The effects of climate change are already obvious, the report warns, with over the last century Auckland's mean annual temperature increasing by 1.6C and sea levels rising by an average of 20 centimetres.
Under current climate trajectory the Gulf would be affected further by rising sea levels and warming sea temperature. More extreme weather events on land could lead to more sediment being flushed into the Gulf, and ocean acidification could adversely affect marine life, particularly those covered in calcium such as shellfish.
The change in temperature and currents could lead to an increase in subtropical/tropical disease and pests.
Report authors warned there needed to be "drastic action" to mitigate the effects of climate change.
The risk of fatal ship strikes on Bryde's whales has been substantially reduced through a voluntarily reduction in the speed of large commercial ships. The lack of ship strikes over the past five years suggests whales can now safely feed and rest within the Marine Park.