The tsunami triggered by a powerful earthquake off the coast of Chile last week has caused minor damage to marine farms in Nelson and Golden Bay, which could now be hazardous for boaties.
Tasman District Council harbourmaster Steve Hainstock has issued a navigation warning for users of Tasman district waters around marine farms, including those in Golden Bay and Tasman Bay, after exceptionally strong currents dislodged elements of the farms.
Hainstock said marine farms had reported line breakages and damage to navigation aids.
Later inspection revealed half-tonne mooring blocks had been dragged around on the sea floor.
There were now loose mussel farming “backbone lines” in the water and navigation lights were either out or missing, Hainstock said.
The lines are anchored to the seabed at one end only, with a buoy on the other and they may present a hazard, particularly to yachts and motorised vessels.
Hainstock was surprised at the damage, particularly as no tsunami warning was issued for New Zealand.
Contractors working on the farms reported sudden, intense currents that were strong enough to pull the light buoys under the water, one by one, he said.
“A contractor on the farm at Collingwood, which is not far off shore, was out doing monitoring work when a surge arrived. He said it was the strongest current he’d ever seen.”
The contractor watched parts of the farm get sucked under the water, Hainstock said. “He watched the light buoys disappear one by one under the water. Some popped back up but others didn’t. That’s quite a significant current.”
Yesterday a yachtsman reported loose lines in the water extending off the farms in Tasman Bay off Port Motueka. Ropes coiled on the farm ready for installation were pulled free by the current.
“There is now 40 metres of lines flapping around,” Hainstock said.
Closer inspection had shown channel markers at the entrance to Collingwood had been “mucked around”.
“Half tonne [mooring] blocks have been dragged around. Only a decent current would have done that.
“It was a sudden current and you certainly wouldn’t have wanted to be in the water or diving at the time.”
Mariners have been advised to navigate with extra caution in these areas until at least April 15.
2014 Fairfax New Zealand Limited