An area of seabed in Tasman Bay will be dredged next week in an attempt to contain a potentially invasive mussel species left behind after an oil drilling company cleaned its rig in the bay late last year.
Mussel farmers in the top of the south have been put on alert for any spread of South African brown mussels from Tasman Bay, with a warning that if the mussel has spawned it could have serious consequences on New Zealand's $200 million greenshell mussel industry.
Tasman Bay and nearby Golden Bay are key aquaculture areas, producing 20 percent of the industry's mussel spat.
The Ministry of Agriculture and Forestry has asked oyster fishers for a 2km "exclusion zone" around the site until the dredging is done on Monday and Tuesday.
MAF's biosecurity incursion response manager David Yard said a 700sq m area of seabed, including a 300sq m buffer area, would be dredged. The dredging would be managed by Nelson's Cawthron Institute.
Biosecurity officials said the South African mussels had been found on December 8 at the site where the semi-submersible drilling ship Ocean Patriot was defouled that month.
The ship was 22km offshore and was getting rid of New Zealand greenshell mussels, at the order of the Victorian state government, before being towed to Australia.
The company that owned the drilling ship had put up $85,000 to cover the cost of the dredging work, and Biosecurity NZ would initially cover any cost over-runs, Mr Yard said. "We don't want cost to be an issue. We will do what ever we can to clean it up."
The work was not expected to have any lasting effects on the Tasman Bay seabed.
Mr Yard said the consequences of the find were still unknown but if the mussels had spawned there was potential for serious economic damage.
The invasive brown mussel competes with other mussels and is difficult to tell from the native greenshell mussel.
The species has recently spawned in North American waters around the Gulf of Mexico and is reported to have become a nuisance at water-cooling intakes for power stations.
"This could have serious economic impact to the mussel growers, because they will no longer (have) pure greenshell colonies.
"I'm reasonably confident that we will get all of them," Mr Yard said. "But if they have already spawned ... then we have much bigger problems".
However, he reiterated the extent of the problem was unknown, and if it was only a couple of mussels that had spawned the spat might not even make it to shore.
The rig had also been moored off Napier, the Wairarapa coast, the Canterbury coast and in Taranaki waters, and Mr Yard said it was possible other sites might be surveyed for brown mussels.
The rig owners, Diamond Offshore Drilling Inc, complained to financial analysts on February 7 that hiring divers and blasters to remove greenshell New Zealand mussels cost it $6.2 million and put the rig out of commission for 23 days.
Diamond Offshore claimed that rough weather meant the defouling could not be done in the open sea. MAF gave the go-ahead to do it in Tasman Bay, as far offshore as possible, based on survey information indicating there were no unwanted organisms on the rig, and the fact that the weather was posing a threat to human safety.
Nelson-based Aquaculture NZ communications manager Chris Choat said it was not known if the brown mussel would survive or how it would adapt to life in NZ waters, and mussel farmers were not blaming MAF.
"They have been operating within their legislation," he said.
The defouling site was outside the territorial waters controlled by New Zealand, and Mr Yard said there were "huge difficulties" caused by a gap in the laws covering the sea beyond territorial waters.
"We are looking at regulating bio-fouling," he said. NZ had asked the International Maritime Organisation to pursue the issue.
- with NZPA
- The Nelson Mail
Decide what news you want to receive when it suits you
Keep up with the latest news by making us your homepage
What do the stars have in store for you today?
Test your mind with our puzzles
The Little Things, Dilbert, Tom Scott and others