Hauraki Gulf

From Our Changing World, 9:20 pm on 26 June 2014

Tawharanui marine reserve with Hauturu/Little Barrier Island in the distance

View across the Hauraki Gulf, from Tawharanui marine reserve to Hauturu-Little Barrier Island (image: A. Ballance)

Each year, an average of two Bryde’s whales are killed in the Hauraki Gulf as a result of ship-strike, but it’s hoped a voluntary transit protocol, which asks commercial ships to slow down in the Gulf, may be the answer to these unwanted whale deaths .

The protocol is the result of several years of collaboration by a working group made up of University of Auckland whale researcher Rochelle Constantine, along with the ports of Auckland and other interested parties.

This collaborative approach of inviting stakeholders to work together to find solutions to difficult problems is one that is being adopted in the Sea Change - Tai Timu Tai Pari -project, designed to develop a marine spatial plan for the Hauraki Gulf.

The Sea Change project began after the most recent State of the Environment 2011 report, about the health and ecology of the Hauraki Gulf, found that ‘most environmental indicators either show negative trends or remain at levels which are indicative of poor environmental condition.’ The Sea Change project was launched last year, and is due to report back by September 2015.

Bottlenose dolphin in the Hauraki Gulf

The Hauraki Gulf is home to bottlenose dolphins, as well as common dolphins and Bryde's whales (image: A. Ballance)

THE HAURAKI GULF – DECLINING HEALTH

The Hauraki Gulf is 1.2 million hectares of sea and islands on the eastern doorsteps of Auckland and Waikato. It reaches north as far as Waipu Cove, includes the Waitemata harbour and the Firth of Thames and wraps around the Coromandel Peninsula.

The Hauraki Gulf Marine Park is ecologically, culturally and economically important. It generates an estimated 2.7 billion dollars of economic activity each year, most of that coming from tourism and recreation, with smaller amounts from commercial shipping, fishing and aquaculture.

A resident population of about 200 Bryde’s whales, along with common and bottlenose dolphins live in the Hauraki Gulf, but the present-day populations of cetaceans in the Hauraki Gulf are much reduced from what they were 1000 and even just 200 years ago. NIWA’s Taking Stock project has been looking at changes in food webs in the Gulf over the last 1000 years, and has found that human settlement has caused substantial changes in the structure of the Hauraki Gulf marine ecosystem. Modeller Matt Pinkerton says the first major changes began within a couple of hundred years of Maori settlement. Hunting led to the local extinction of seals and sealions, while the introduction of kiore or Pacific rats caused widespread declines in the breeding populations of burrowing seabirds.

European settlement after 1790 caused a new wave of significant population declines, such as the local extinction of southern right whales as a result of whaling, and a very significant decline in the humpback whaling population. Fish stocks, especially snapper, have declined as a result of commercial and recreational fishing. Snapper stocks now are estimated to be just 16% of what they were 1000 years ago.

As marine wildlife in the Hauraki Gulf has declined, the human population has been growing rapidly, and along with that there’s been a growing use of the Gulf by commercial ships. Matt Ball from the Ports of Auckland says more than 1500 large container ships transit through the Gulf each year, moving about 900,000 containers..

The Hauraki Gulf is a hotspot for seabirds, and Forest and Bird’s seabird advocate Karen Baird says many people don’t appreciate what a diversity of seabirds feed and breed in the Gulf. Twenty seven of New Zealand's 85 breeding species of seabird breed in the Hauraki Gulf. However, some species such as black petrels, that breed only in the Gulf, are now classified as threatened.

Rsearchers from Dragonfly Science recently calculated that large numbers of black petrels were being accidentally caught on hooks set by the commercial fishing fleet working in the Hauraki Gulf. Now, however, the fishers are working with groups such as Southern Seabird Solutions to develop seabird–friendly fishing methods. Recent surveys have also showed that recreational fishers have been accidentally catching significant numbers of seabirds.

NIWA’s Bruce Hartill has been studying the size and impact of the recreational fishing sector on fish stocks, using methods such as aerial surveys of boats. On a fine weekend day NIWA’s aerial boat survey routinely count more than 2000 boats out fishing, while on the busiest day they recorded 3600 boats out in the Gulf.

The decrease in the stocks of snapper and also crayfish has had significant effects on reef ecosystems across the Hauraki Gulf. For many years marine biologist Roger Grace has been monitoring the Tawharanui marine reserve, and he says that since fishing was banned in the reserve the kelp forest has returned as the numbers and size of snapper and crayfish in the reserve have increased. Roger Grace, who is a strong advocate for the value of fully protected marein reserves, says it takes about 15 years of ‘no take’ protection for the kelp forest to begin to improve, as only large fish and crayfish are capable of eating the large kina or sea urchins.

NIWA’s Mark Morrison says many of the changes to the ecology of the Hauraki Gulf are subtle and out of sight. Sedimentation as a result of land use changes, especially deforestation, has been significant and widespread. Dairy farming on the Hauraki Plains is the source of significant levels of nitrate runoff, while Auckland’s large urban population produces pollution such as heavy metals.

GREEN LIPPED MUSSEL BEDS IN THE FIRTH OF THAMES

Green-lipped mussels once played a significant role in the Hauraki Gulf marine ecosystem. Darren Parsons from NIWA says that the floor of the Firth of Thames used to be covered in mats of green-lipped mussels that attached to each other in big ‘carpets’. Commercial dredging saw the removal of almost all the mussels by the 1960s, and although there has been no further dredging the mussel beds have not begun to re-establish. It has been estimated that the former mussel beds could filter all the water in the Firth of Thames in a single day, while the remnant beds would take several years to filter the same amount of water.

The Revive our Gulf group recently introduced several tonnes of green-lipped mussels into an area of seafloor  near Waiheke, and are monitoring to see if a larger scale mussel bed restoration could be feasible.

Ports of Auckland wharf with container ship

More than 1500 container vessels transit through the Hauraki Gulf en route to Ports of Auckland each year (image: A. Ballance)

BRYDE’S WHALES AND THE TRANSIT PROTOCOL FOR COMMERCIAL SHIPPING

Research by Rochelle Constantine and her students at the University of Auckland found that Bryde’s whales spend most of their time between the surface of the water and 12 metres down. The maximum draught for large commercial ships in the Hauraki Gulf is 12 metres, which means that the whales spend most of their out of sight but at a depth where they could be hit by a ship.

Rochelle Constantine and one of her students calculated the effect of ship speed on the issue of ship strike on whales. Using AIS - the Automated ID System that identifies ships at sea - they worked out that average ship speed in the Gulf was 13.2 knots. They then calculated the risk that a whale would be killed if it was hit by a ship at that speed was 51%, while the risk of death to a whale from a ship travelling at 10 knots was just 16%.

Further research showed that the whales concentrated their activity in hotspots, but these hotspots varied from year to year and were generally in areas frequented by boats. Overseas, shipping lanes have been re-routed so large ships can avoid areas favoured by whale species such as northern right whales, but the distribution of whales in the Gulf meant this was not an option.

Because slower speed means longer transit times commercial shipping companies were initially reluctant to slow down but Ports of Auckland and a working group of interested parties reached a workable compromise – a voluntary transit protocol which asks ships to speed up outside the Gulf so they can arrive early and have a slower trip through the Gulf. The Dolphin Explorer whale and dolphin safari boat and others also radio through the location of whale sightings, and the Ports of Auckland passes these alerts on to commercial shipping.

Downtown Auckland city from the sea

The Hauraki Gulf is 1.2 million hectares of sea and islands bordered by Auckland city, the Waikato and Coromandel Peninsula (image: A. Ballance)

THE SEA CHANGE PROJECT

Hauraki District Mayor and chair of the Hauraki Gulf Forum John Tregidga has been instrumental in setting up the Sea Change project, which aims to address the ongoing decline in the health of the Hauraki Gulf by developing a marine spatial plan.

There are two tiers to the Sea Change process. The Stakeholder Working Group is 14 people from a range of interest and user groups: mana whenua, aquaculture, fishing, recreation, industry, tourism and conservation. Nick Main is the independent chair working with the stakeholder working group as they collaborate on developing the marine spatial plan.

The Project Steering Group provides leadership and will ultimately recommend to councils and other agencies how the marine spatial plan can be put into practice. It includes representatives from mana whenua, Hauraki Gulf Forum, Auckland Council, Waikato Regional Council, Ministry for Primary Industries and Department of Conservation.

A marine spatial plan for the Hauraki Gulf will have to accommodate many competing uses: marine reserves, marinas, marine farms, recreational and commercial boat use, and fishing, to name just a few. It will also have to be able to cope with everything that is happening in the catchments that feed into the gulf, including a large and rapidly growing urban population and intensification of farming. Small collaborations – the transit protocol to prevent more whale deaths and a trial establishment of green-lipped mussel beds – show what’s possible but trying to improve the health of the Hauraki Gulf is a monumental and urgent task.

Hauraki Gulf dolphin safari - tourists watching bottlenose dolphins

Tourists on board the Dolphin Explorer enjoy an encounter with a pod of bottlenose dolphins near Motuihe Island in the inner hauraki Gulf (image: A. Ballance)