Marlborough ecosystems being destroyed

Sedimentation caused by forestry activities at Hitaua Bay in the Marlborough Sounds.
ROB DAVIDSON

Sedimentation caused by forestry activities at Hitaua Bay in the Marlborough Sounds.

Significant marine ecosystems in the Marlborough Sounds are being degraded or lost at an alarming rate, a new report shows. 

Marine biologist Rob Davidson said more than 1431 hectares of sea bed ecosystems, the size of Blenheim and its suburbs, had disappeared in the Sounds since the late 1980s.

Nine sites, ranked as significant because of their biological values, had decreased by 71 per cent.

Anchor damage to Perano Shoal in the Marlborough Sounds.
ROB DAVIDSON

Anchor damage to Perano Shoal in the Marlborough Sounds.

Those worst affected areas were deep, off shore, soft bottom sites, Davidson said.

Five sites at Port Gore, Ship Cove to Cannibal Cove and Hitaua Bay Estuary showed a decline in size because of trawling, dredging, and sedimentation from forestry activities. 

Sedimentation from logging was smothering some ecosystems and trawling and dredging from commercial fishing saw anchors being dragged along soft sea floors damaging vulnerable habitats, Davidson said.

It was the first time the level of degradation had been revealed.

Presenting the report at the Marlborough District Council's environment committee, he said his findings were demoralising.

If the council did not move to protect off shore soft bottom habitats that support medium and high biological values they would continue to disappear, he said.

Davidson analysed 21 significant marine sites in Queen Charlotte Sound, Tory Channel and Port Gore and compared them with 2011 data. 

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Sedimentation caused by forestry activities saw large volumes of fine sediment smother and clog low-lying estuaries, reducing their productivity, Davidson said.

Oyster wraps in Kaiuma Bay had gathered up 0.7 metres of sediment in four years.

It damaged habitats, removed species and destabilised the sea floor.

Dredging from commercial activity and anchors dragging along the sea floor threatened habitats.

Fourteen per cent of Perano Shoal in the Marlborough Sounds was damaged by anchors scouring out channels, threatening fragile dense tubeworm mounds.

Davidson urged council to retain the most significant sites.

"Despite the intense and widespread level of human pressure and the knowledge that few significant sites remain, there is a poor record of marine protection in Marlborough."

Only Long Island-Kokomohua Marine Reserve was protected out of 127 significant sites.

"We have to concentrate on what we have left, rather than what we have lost.

"If we don't do anything they will gradually be degraded and lost. We can't sit and hope.

"New legislation is not good on this. If we created 127 marine reserves people would throw rocks at us. We need a wider mechanism."

Considerable attention had been given to blue cod stocks in Marlborough Sounds, by placing size limits, fishing seasons and bag limits on recreational fisherman.

Virtually no attention had been given to protection of adult and juvenile blue cod habitat, Davidson said

Blue cod regularly inhabit soft bottom habitats and it is these habitats that are under serious threat and declining, Davidson said. 

"We don't want to stop people fishing. Line fishing is OK. 

"Stopping anchoring is not too hard."

In Perano Shoal, protection could be as simple as a habitat protection zone where anchoring was banned.

Council coastal scientist Dr Steve Urlich said the report had pulled back the aquatic curtain in Marlborough for the first time.

"Because sites are unseen we are unaware our collective impact is causing severe disturbance and decline of our most significant habitats, of which there are relatively few remaining. If we think about these habitats as Marlborough versions of coral reefs, which are being damaged and destroyed, they need protection and restoration."

Council did have powers under the Resource Management Act to control seabed disturbance and council was considering that in the review of the Marlborough Resource Management Plan, Urlich said.

Environment committee chairman Peter Jerram said the speed of deterioration was startling. 

"We have 19 per cent of New Zealand's coastline and one marine reserve. That's a national and regional disgrace."

 - Stuff

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