Kaipara Harbour rescue

Ngati Whatua farm manager Ray Monk with his dogs on Otakanini Topu, South Head, overlooking the Kaipara Harbour. Photo / Jason Oxenham

One of our most important but overlooked harbours is at risk of drowning in a sea of mud. But, as Geoff Cumming learns, a partnership approach is beginning to stem the tide.

It's a marine ecological gem on the doorstep of our biggest city and it's not the Hauraki Gulf. Tucked away on the road less travelled, the Kaipara Harbour is our biggest estuary and the second biggest "enclosed" harbour in the southern hemisphere.

The variety of estuarine habitats supports a diverse array of species - ensuring the Kaipara's influence as incubator and nurturer of marine and terrestrial life ripples well beyond its shores. Most snapper in the west coast North Island fishery are born here. Great white sharks have their pups here. Arctic migratory birds including bar-tailed godwits and red knots are among the thousands of wading birds that forage on the inter-tidal flats and fatten on the foreshore.

The key coastal habitats - salt marshes, mangroves, mudflats and dunes - form an effective barrier between people and sea but this isolation is both blessing and curse. Only now are humans waking up to the degradation they have caused.

Though the harbour extends 60km from north to south, its Tasman Sea entrance is just 5km wide at the narrowest point, limiting its flushing ability. The harbour covers 947 sq km but at low tide nearly half is exposed. Inter-tidal and sub-tidal flats are key ecosystems but are slowly being smothered in sediment and harmful nutrients washed down a vast 6400 sq km catchment.

A symposium next weekend organised by iwi-backed Integrated Kaipara Harbour Management Group will shed light on the state of the harbour and look for solutions based on Maori concepts of kaitiakitanga (guardianship and sustainable use) and partnership. Talk to some of the players, it's soon clear these concepts are long overdue.

The catchment extends from the Russell Forest in Northland to the lifestyle blocks of west Auckland. A 9000km-long network of streams and rivers through the catchment are veins that feed the harbour, says IKHMG co-chair Chris Pairama. After 150 years of development, from forest clearance to farming, quarrying and urbanisation, the veins are far from healthy.

Pastoral farming - increasingly dairying - covers 53 per cent of the land. Most main rivers run brown with fine sediment and contaminants by the time they reach the harbour, worsening water quality and clarity and degrading habitats.

"It's an environmental and economic conundrum," says Pairama, of Nga Rima o Kaipara, a Ngati Whatua hapu whose rohe (domain) includes the southern Kaipara.

"The farmers have user rights - they've been doing it for generations, it's New Zealand's biggest export earner. But when you consider the size of the catchment it's the cumulative effects of each farm. It's been forgotten about for so long. We've been dumping nutrients in it for so long."

Pairama, an environmental consultant, is not anti-farming - he's admiring the view from Otakanini Topu, a Ngati Whatua farm covering 2800ha which drains into the southern Kaipara near Parakai. "It's about finding a balance - about sustainable farm practices," he says.

"We need to slowly chip away at the old block. We have to stand up before we lose the Kaipara completely."

The problem, however, stems not just from farming but the legacy of sediment working its way downstream since native bush clearance began in the 1850s - not helped by steep, erosion-prone slopes and underlying geology. Some of the marginal land is only now being retired.

Rural subdivision, pine forest harvesting and quarrying are additional past contributors.

Sediment is accumulating on the harbour floor at 10mm a year - about 10 times the rate before forest clearance, says Niwa principal scientist Mal Green. That adds up to half a metre of mud over 50 years - enough to cause catastrophic impacts on some benthic (seafloor) habitats. The spread of mud promotes the march of mangroves, changing biodiversity.

Other economic uses to threaten harbour ecosystems include sandmining, over-fishing and the tidal power plant planned for the harbour entrance - which gained approval despite concerns about electromagnetic impacts on species navigating the harbour entrance, from spat to maui's dolphins and whales.

Weak and fragmented past governance and limited research funding have let the harbour down - split responsibilities and differing agendas bringing inconsistency and confusion, with more than 70 statutory and planning documents affecting catchment management. New rules requiring councils to set bottom lines for freshwater quality are hazy about impacts on estuarine health.

It's the inter-tidal and sub-tidal flats that make the harbour so important, Green says. Salt marshes and mangroves provide habitat for benthic creatures ranging from tiny burrowers and rare tube-building worms to bivalves - prey for fish and birds. Seagrass meadows are a nursery for infant snapper, rig and other fish - the Kaipara has the most extensive seagrass beds left among west coast harbours.

"There's a massive diversity of habitats that makes the harbour special," Green says. "There are big open parts where the large volume of water dilutes nutrients but also closed embayments that are poorly flushed where the sedimentation is very high.

"The combination is quite important but it's also quite vulnerable." Suspended fine sediments not only hinder filter feeders, they reduce water clarity and quality, affecting aquatic plants such as seagrasses and animals that need light, with impacts spiralling up the food chain. Farm nutrients - including nitrogen and phosphorus - and faecal contamination further reduce water quality.

Evidence of decline is both anecdotal and science-backed. A 2005 stock assessment for the west coast North Island snapper fishery estimated stocks were as low as 8-12 per cent of the pre-fishing biomass, despite measures to rebuild the fishery. Commercial and recreational allowances were further cut but any revival is some years away.

In a new report on Kaipara habitats for the Ministry of Primary Industries, long-time locals report fundamental declines in seagrass meadows, fish size and abundance and shellfish gathering areas - "large schools of big snapper no longer feeding in very shallow waters, dense scallop beds once, but no longer, associated with the grasslands".

The report led by Niwa marine ecologist Mark Morrison found sedimentation was the biggest threat to the Kaipara's function as a critical nursery for rig, school sharks and other commercial species.

Increased water quality monitoring has exposed a distressing pattern, with nitrogen, phosphorus and turbidity readings routinely exceeding guideline limits in most monitored waterways. As monitoring website lawa.org.nz (Land and Water Aotearoa) reveals, 10-year trends in many rivers are worsening, despite increasing community efforts to turn things around.

Meandering through intensive dairying country west of Whangarei, the Mangere River is ranked in the worst 5 per cent of Northland waterways, with excessive levels of nitrogen and E.coli and dangerously low levels of dissolved oxygen. Further downstream, phosphorus and turbidity levels become unacceptable. Fish and eels are still found but the turbidity means fewer banded kokopu juveniles make the annual migration to grow in the Pukenui Forest.

The Northland Regional Council has made this 7650ha area, containing 19 dairy farms plus beef and sheep farms, one of five priority catchments under its Waiora programme. Most farmers and the wider community are on board with better effluent controls, fencing off streams and riparian planting. But a council report notes livestock still have direct access to the river in places, eroding banks and increasing sediment loads.

The Mangere feeds into the Wairua - already laden with sediment and nutrients from the Hikurangi farming district - which joins the Northern Wairoa River near Dargaville. The mud-brown river drains 63 per cent of the catchment and is the Kaipara's biggest source of sediment, which is spread by currents as far as the southern shores. Suspended sediments pouring from the Northern Wairoa during floods have smothered habitats, largely confining juvenile snapper and other fish to the harbour's southern half.

But in the south, where rural subdivision is an additional pressure, the Hoteo, Makarau, Kaukapakapa and Kaipara rivers also carry significant sediment loads, coating once sandy tidal flats in mud.

Throughout the vast catchment, efforts are under way to turn things around. Auckland Council last year injected $130,000 over three years to help restore the Hoteo, whose sediment threatens key seagrass beds off the river mouth. Landowner restoration work is under way in the neighbouring Araparera catchment, where the IKHMG has two flagship farms.

Fonterra and DoC have included the Hikurangi district in their Living Waters programme, one of five catchments nationwide in line for $20 million funding over 10 years. Given the scale of the problem, it may seem a drop in the bucket but an Open Day last month highlighted community and farmer interest in measures such as planting native trees on banks.

There are always cowboys. A Dargaville farmer who carried out excavations including river reclamation and causeway construction over an 18-month period without sediment controls was in June fined $54,000, the Northern Advocate reported. "At best there was a complete lack of care on his part and at worst downright recklessness," Environment Court Judge Brian Dwyer concluded. Northland Regional Council has prosecuted a handful of other farmers in the past three years for discharging effluent into waterways.

But most farmers are keen to improve land, stock and effluent management and undertake riparian planting - the latter encouraged by council grants and tax breaks.

On Otakanini Topu, the Ngati Whatua farm near Parakai, farm manager Ray Monk has his work cut out. The 2800 ha spread includes erosion-prone pasture on unstable sand hills. When he arrived three years ago, heavy cattle roamed the high country and defecated in unfenced wetlands beside the harbour. Monk had the farm and its soils profiled before destocking and fencing off some areas; intensifying in others. Native trees were planted to stabilise steep slopes. With council help, waterways were fenced and the main wetland - once a bog which dried out in summer - is thriving.

The farm mix is mainly sheep and beef and Monk is committed to farming sustainably. "I love doing it but at the end of the day I am paid to run a profitable business. We are showing that it can be done."

Otakanini Topu is one of nine "flagship farms" promoted by IKHMG to demonstrate best practice in sustainable farming. Three are Ngati Whatua, the rest privately owned and operated.

A limestone quarry has also signed up and next year the group hopes to get a marine site established.

That the IKHMG is seeking to revive the harbour using Maori kaupapa (principles) is appropriate. The harbour is taonga to Te Uri O Hau and Nga Rima o Kaipara but, until recent treaty settlements, both these Ngati Whatua hapu and the harbour were struggling against the tide of Pakeha-led economic use.

Since IKHMG formed in 2005, Crown agencies and councils have increased their focus on catchment restoration and research - and they are talking to each other.

"The biggest milestone has been the partnership that's formed between hapu and stakeholders," says IKHMG co-ordinator Leane Makey. "It has meant the Maori world view is acknowledged alongside Western science."

Next weekend, the IKHMG will host Looking Back, Thinking Forward, the first major symposium to focus on the health of the Kaipara. The two-day event at Te Ao Marama Maori Cultural Centre in Te Hana will highlight current knowledge of harbour ecosystems and look to forge further research and partnerships.

More information: www.kaiparaharbour.net.nz.