Eradication of Asian seaweed planned

Forest and Bird, Issue 293, 1 August 1999, Page 7

Eradication of Asian seaweed planned

DoC, Southland.

—Tom O'Connor,

e Department of Conservation has been asked to lead a joint project to eradicate the exotic seaweed undaria from Stewart Island waters. The Asian seaweed was discovered at Big Glory Bay, inside Paterson Inlet, in 1997. The invasive algal weed is thought to have arrived in New Zealand via the hulls or ballast tanks of international ships, and was discovered in east coast harbours from Napier to Lyttelton in the late 1980s. The bottom-smoth-ering weed has since turned up in more exposed and widespread places. Its discovery on marine farm buoys and ropes in Big Glory Bay brought a swift reaction, and the department’s Southland Conservancy was called in to set up a joint eradication trial with the regional council and marine farmers. Conservator Lou Sanson says Stewart Island marine ecosystems are recognised internationally for their relatively pristine and natural condition.

"Undaria is a very aggressive species and could displace native seaweeds and the marine life which rely on them. Kina, paua, crayfish and our indigenous fish species have evolved a complex inter-relationship which could be seriously disrupted if this seaweed is allowed to become established in Stewart Island waters. Weare currently working on the establishment of a marine reserve in Paterson Inlet to protect the native marine ecology, and the last thing we want is an invasive seaweed taking over; he says. A team of divers has spent the last year laboriously picking plants from hundreds of metres of mussel farm ropes, buoys, fish cages and the sea floor. Marine farmers cooperated by removing a number of heavily infested barges and other floating equipment from the water, and have assisted the department’s diving team. Lou Sanson says early advice suggested eradication was probably not achievable, and that a control programme was the

best that could be expected. "The hard work over the past year has altered that perception. We are now more confident, given the results the diving team has achieved to date, that we can get the last plant in Big Glory Bay. It is, however, an expensive operation but we are going to continue for another growing season and re-evaluate the situation again later this year’

The 1999 Budget included $2.177 million to fund the costs of eradicating undaria from Stewart Island over five years. The weed will also be eradicated from Bluff Harbour on the adjacent mainland to prevent reinfestation across Foveaux Strait. Undaria has already spread along several other coasts of mainland New Zealand, however. Puzzlingly, in Wellington, the regional council has even encouraged its management as a commercial product by permitting a marine farm to harvest undaria for export. — Editor.