Two unwanted marine pests appear to be gaining the upper hand in Southland's coastal waters, with Environment Southland (ES) today (16 Nov) accepting Stewart Island's Carpet Sea Squirt may be here to stay and announcing that the invasive seawed Undaria has now been found at a third location in Fiordland.

Carpet Sea Squirt (Didemnum vexillum) was first discovered in Rakiura/Stewart Island waters in July 2022 and because of its exclusion pest status, prompted an emergency biosecurity response from ES.

However at today's (16 Nov) ES Strategy and Policy committee meeting, ES biosecurity and biodiversity operations manager Ali Meade said advice given by the technical advisory group during the response concluded that eradication of the pest was unlikely due to its spread. However, it may be possible to contain the extent of incursions and prevent further damage to pristine marine environments.

“While we are accepting the presence of this pest in Big Glory Bay, we will continue to monitor it, educate the public and business, and attempt to contain it," she said.

The committee decided to relax its approach to the marine pest, approving a move to actively prevent Carpet Sea Squirt's spread from Big Glory Bay in the short term, and working towards removing its exclusion status in the next few years.

A change in pest status would require a formal review of the Southland Regional Pest Management Plan.

Meade said removing carpet sea squirt from the plan did not mean it would be left to spread throughout the region.

However Meade was unsure if a new discovery of Undaria, found on 9 November on the south side of Resolution Island, was a jump from the established containment area or a new incursion.

ES, Biosecurity New Zealand (BSNZ), the Department of Conservation and the Fiordland Marine Guardians have been working together on an intensive control programme for Undaria in Te Puaitaha/Breaksea Sound since 2010 and Taiari/Chalky Inlet since its discovery there in 2019, she said.

Undaria. Photo: K Blackmore/DOC

A new two-year trial piloting a suppression tool on Undaria in Te Puaitaha/Breaksea Sound was also underway.

Meade said the latest discovery reinforced just how important it was for all vessels to abide by the rules of the Fiordland Marine Regional Pathway Management Plan to stop pests getting into the pristine waters of Fiordland. 

“The plan requires all vessels entering within one nautical mile of the landward boundary of the Te Moana o Atawhenua/Fiordland Marine Area to hold a Clean Vessel Pass, and to comply with clean vessel, clean gear, and residual seawater standards.”

Fiordland Marine Guardian chair Rebecca McLeod said the new discovery of Undaria was devastating.

“While we are uncertain about what this will mean for the Undaria work already underway in Te Puaitaha/Breaksea Sound, vessels must continue to be vigilant about marine pests when they travel into the fiords.“

“Undaria is just one of several highly invasive marine pests in New Zealand waters, and we need to make every effort to reduce the risk of anything being carried into the Fiordland Marine Area. In the case of Undaria, we don’t want to hasten its spread by shifting it outside of an infested area,” Dr McLeod said.