A Western Bay conservationist has criticised a plan to use a hovercraft to eradicate mangroves in the Tauranga Harbour saying it will further threaten a rare native bird.
More than $250,000 will be spent on a hovercraft to eradicate mangroves in the harbour where the banded rail seeks shelter and food.
Bay of Plenty Regional Council is working with Fieldmaster, an Auckland based company which specialises in high-tech mowing equipment, to develop a hovercraft which will mow down areas of regenerated mangrove seedlings in the Tauranga Harbour.
The hovercraft will have a front-mounted mowing system which will cut mangrove seedlings below their lowest leaves.
Trials for the machine should begin in August or September this year with council hoping the hovercraft will be in action by March next year.
Warwick Murray, Environmental Delivery general manager, said once in operation the hovercraft mower will be in operation for six months every year.
"It is expected to be able to complete annual mowing in each of the areas consented for seedling control, totalling 600ha which are located in parts of 11 estuaries within Tauranga Harbour.
However, he said hovercraft mowing will stop for the bird breeding season, from August to February, each year.
Regional Council had carefully considered the costs and benefits of mechanical seedling control, he said.
"There was a comprehensive monitoring programme to ensure the effects of the machine on estuarine birds and shellfish are no more than minor.
"Due to its speed, design and low PSI of 0.1, the hovercraft will leave no discernable 'footprint' on the estuary surface," Mr Murray said.
However Basil Graeme a veteran Tauranga environmentalist said mangroves were not only important for the environment but also a vital habitat for the banded rail.
"It's a threatened bird, they have been described as mangrove dependent.
"They have disappeared from practically all the wetlands around the place unless mangroves are present."
Mr Graeme said the little bird, known to be extremely shy and secretive, used mangroves for protection from predators and would hunt crabs, one of its food sources, from underneath their roots.
Mangroves were also an important absorber of carbon dioxide, Mr Graeme said.
"As the stock grows up they are storing carbon not just in the mangrove plants but in the roots but they are also storing carbon in the sediment. They are one of the most important carbon storage bits of vegetation that we've got.
"Regional council is meant to be planning a 100 years ahead for climate change but they are going ahead and mowing down mangroves which could be absorbing all this carbon if they let them grow," Mr Graeme added.