14 March 2008

Good progress on biosecurity mussel dredging in Tasman Bay

The MAF Biosecurity New Zealand (MAFBNZ) dredging of the Tasman Bay site where an oil rig was cleaned late last year is progressing well.

The removal of material from the drop zone beneath the rig defouling site is to reduce the biosecurity risk posed by a South African brown mussel that was thought to be on the rig at the time it was cleaned.

The mussel, Perna perna, is listed on a world database of invasive species, although it’s not known how it would perform in the New Zealand environment.

An area of around 250,000 square metres of seabed is being dredged by a scallop dredge, which has been at work in the area a week. Each day the dredge has been at work it has brought ashore some three tonnes of debris for disposal at a local landfill. Work is expected to be finished at the site next week, weather permitting.

MAFBNZ Incursion Response Manager David Yard says as the work progresses, some mussel specimens from the dredge material are being retained for further scientific examination.

“So far, of the mussels found, less than one percent are what could be described as “potentially” South African brown mussel Perna perna. This is because they look slightly different to the native green lipped mussel, Perna canaliculus. Definitive identification of these suspect mussels is, however, proving challenging as they are so similar to Perna canaliculus. Genetic testing is underway to provide a definitive identification.”

Analysis of mussel samples dredged from the area for analysis in mid February, and which prompted the dredging clean up, are still undergoing identification.

David Yard says after the sample taking there were two suspicious specimens. One of those has now been formally identified as the New Zealand Perna canaliculus and the other specimen has been tentatively identified as Perna perna, however MAFBNZ is awaiting results of genetic testing to be sure of this diagnosis – this illustrates just how difficult Perna perna is to distinguish from its native relative.

Once dredging is completed at the main rig defouling site, MAFBNZ will be scoping up a similar clean-up at an initial site where the rig commenced its defouling before moving to shelter closer inshore.

David Yard says preliminary information was that divers were only working at this initial site for a matter of hours, but it has now been confirmed that defouling was underway there for a week, making it important to also treat this location,

A further meeting to update concerned individuals in the Nelson/Marlborough/Tasman area is being planned for next week.

ends

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