Developers, farmers claim they are not to blame for harbour contamination
It's the first home for the majority of the North Island's west coast snapper, and it's under threat - but farmers and developers deny they're contaminating the Kaipara Harbour.
The Kaipara Harbour is both a nursery and feeding ground for snapper. A Niwa report from 2009 said 98 per cent of all adult snapper caught from Ninety Mile Beach to Mana Island in Wellington were originally from Kaipara Harbour.
The Niwa report said Kaipara Harbour was under threat from human activities – particularly land uses which caused sedimentation and changes in water quality. These effects could all damage the nursery habitat of snapper, usually seagrasses and horse mussel beds, the report said. Negative impacts on juvenile fish in the harbour would cascade through to a much larger ecosystem.
Rodney Local Board deputy chairman Phelan Pirrie said cattle urinating and defecating in streams were contributing to nitrogen making its way into the harbour, putting snapper stocks at risk.
The board wants to tackle the contamination at its source - offering to match every dollar farmers in the north-west spend fencing off waterways.
Pirrie said silt run-off was damaging the seagrass where the snapper live, increasing the risk of fisheries declining.
"We need to keep stock out of the rivers," Pirrie said.
"Every time I drive up to council I see them [cattle in streams]. That's an issue and we want to do what we can to encourage farmers to do that fencing that is required."
The board was proposing a $250,000 fund be put together for the next financial year - beginning in July 2017 - to address the problem.
The fund doubled the board's usual environmental budget, and used up its common development budget.
Pirrie said Niwa reports indicated nitrogen run-off was part of the harbour's degradation problem, and nitrogen tended to come from cattle.
But senior policy advisor for Federated Farmers, Richard Gardner, said cattle was not the biggest issue for the Kaipara Harbour.
Gardner said sedimentation from developments was the main contaminator of the harbour, and the change from rural land to urban land contributed.
"You've probably seen how they take off all the topsoil and are left with the bare clay while they prepare to do earthworks and then cover it up. That can give rise to quite a bit of sediment. They do a lot of work on that to prevent the run-off but they can't do it all," he said.
Gardner said fencing requirements only stated that flat farm land needed to be fenced, not steep land.
General manager of north-west property developer Cabra Developments, Lloyd Barker, said its consents required the company to construct temporary silt ponds with flock treatment and silt fences.
These were designed to remove 95 per cent of silt generated and were regularly monitored by Auckland Council, he said.
Previous studies had shown that once houses are constructed in a subdivision, and the grounds established, the silt run-off is significantly lower than the same area of rural land, Barker said.
He said in the Kaipara River catchment urban land was only a "very small percentage" of the total land draining into the harbour.
Cabra has worked on sites in Huapai, Riverhead, Wainui and Orewa.
Pirrie agreed there were a number of issues with the harbour.
He said the board aimed to focus on the harbour's health over the next few years to see what it could do to make a change.