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Fairy tern trust has doubts over MHRS mangrove study




thumbnail 04 MF-FairyTreply2-291Following the recent study by Mangawhai Harbour Restoration Society (MHRS) which outlined positive findings regarding local mangrove management [Focus, Feb 10] the Focus approached another environmental guardian group for their perspective.

New Zealand Fairy Tern Charitable Trust (NZFTCT) convenor Heather Rogan says although having some doubts regarding the study, the organisation actually has ‘no problem with mangrove management’.

“As long as it doesn’t cause any harm. It is to be hoped that by ‘mangrove management’ the MHRS don’t mean wholesale or large-scale mangrove removal, as this did have a detrimental effect on NZ fairy tern breeding success in Mangawhai, normally the bird’s most significant breeding area.”

Succeeding the extensive 2015 mangrove removal, a decline in the breeding success of the endangered birds was immediately noticed Rogan says, with the number of fairy tern eggs laid on Mangawhai Spit ‘plummeting to only five compared with 18 the previous season’.

“Unfortunately the decline continued in subsequent years with the 2018-19 season being the worst on record for Mangawhai fairy terns – no chicks fledged here that season,” she says. “That is why we have misgivings about the reliability of the MHRS survey when it claims that mangrove removal has been beneficial for NZ fairy terns.”

Teetering on the brink of extinction since the 1970s, fewer than 40 adult fairy terns or ‘tara iti’ are now alive despite intensive management programmes. Based in Mangawhai, NZFTCT was created in 2008 to work with Department of Conservation to help protect the critically endangered birds whose main threats include predators and loss of, and disturbance of, habitat. Mangawhai fairy terns nest along the Sandspit where the Trust has managed a successful year-round predator control programme which has seen no loss of birds, chicks or eggs to introduced predators since 2012. Due to their fish-only diet the fairy terns are dependent on the harbour and for the past three breeding seasons Trust volunteers have conducted a survey of the birds’ aquatic feeding grounds.

“Mangroves seem to get bad press in Mangawhai with some people even trying to claim they are not native to New Zealand! A hard claim to understand when records show they have been here for some 19 million years,” Rogan says. “Some communities in Northland value their mangroves and it’s easy to see why when you consider their benefits.”

Besides providing a nursery and a shelter for fish, the plants are a habitat for endangered, reclusive birds such as bittern, banded rail and fernbird, Rogan says.

“Just because birds are hidden in the mangroves doesn’t mean they‘re not there.”

Mangroves also form a protective barrier for saltmarsh, filter sediment and pollutants keeping harbours clean, reduce erosion by calming wave action, ‘have you noticed the erosion of the

causeway since mangrove removal?’ and with sea levels rising ‘their protective, buffering role will become increasingly important’ she says.

“Their honey is said to be delicious, on a par with manuka honey and they provide a peaceful, sheltered environment, where passive recreation can be enjoyed… kayaking and paddle-boarding through mangroves at high tide is heaps of fun,” she says. “However, we do understand that the unchecked spread of mangroves can be a problem… a focus on prevention, rather than cure, may be the answer.”

¢ To read ‘Mangroves in NZ – Misunderstandings and Management’ by Dr Sharon De Luca, visit boffamiskell.co.nz/downloads/publications/mangroves-in-nz-misunderstandings-and-management.pdf

Waterway planting to stop mangrove march

Among the muddy controversy of mangroves’ environmental value and what to do about the plants prolific spread, a long-time Mangawhai resident says the way to halt the march of the mangroves is not through removal, but by planting out the areas waterways – riparian planting.

“In the 1950s and early 60s, land was still being cleared of gorse and scrub for pasture, and there were many small airstrips in the district with small planes buzzing overhead for a number of years spreading fertiliser on new farm areas as well as existing farms,” the local woman says who prefers to not be identified for personal reasons. “It was about this time that mangroves were reported to be on the increase.”

For many years fertiliser poured on surrounding land, as well as animal excrement and sediment flushed with heavy rain, has been trickling down to the harbour via the many minute streams, where mangroves have been ‘doing their job’ by filtering the flow and keeping the harbour clean’. The local says ‘it is totally inappropriate’ to pull mangroves out of the harbour before cleaning up the water upstream, as the mangroves ‘will just keep growing again’.

“Riparian planting will help. It takes time to be effective, about 10 years, but it is a start; visit Raglan Harbour if you want proof. The entire stream system over years has been planted by the community and the harbour is now really clean,” she says. “Come on MHRS! Stop wasting our ratepayer money pulling out mangroves! Be constructive, plant instead!”

“Some communities in Northland value their mangroves and it’s easy to see why when you consider their benefits.”

-- Heather Rogan


Under constant threat of becoming extinct, NZ’s rarest endemic breeding bird, the fairy tern. Heather Rogan says although ratepayers contribute $80 per year to the Mangawhai Harbour Restoration Society, they have no control over how their money is spent. “We would like to see the society consult more widely with groups such as ours, who have a legitimate interest in the health of the harbour.”

PHOTO/Darren Markin 2019


For more on the importance of rural minor waterways, see ‘Stock grazing muddies local waters’, Mangawhai Focus, Feb 10 issue, page 1

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