The expansion of Stewart Island's invasive seaweed, Undaria, seems to have halted following the results of the latest survey conducted in early January by Environment Southland (ES) divers.

Divers spent a week surveying Rakiura/Stewart Island's southern coast and found no sign of Undaria in Broad Bay, where a previous incursion was identified in 2020.

And while a check on Easy Harbour found some regrowth of Undaria, it was at much lower densities than when it was discovered in 2022. That regrowth was removed.

ES biosecurity operations manager Ali Meade said all Undaria was removed and no further expansion of the population was identified.

“The reduced number of plants and density is a good sign that our work to eliminate the incursion is on track. Follow-up removal efforts will be required to ensure elimination from the site.”

“This is a great result and shows what can happen with quick efforts to remove the invasive species. Further surveillance will be required to confirm complete elimination over the next few years but it looks promising.”

The final part of the dive trip was to survey key anchorages around the southern coast of Rakiura and within Port Pegasus for Undaria, carpet sea squirt and other marine pests.

“No Undaria was found at the sites inspected around the southern coast or in Port Pegasus. Some sea squirts were found in very low numbers but were not positively identified as the invasive species, carpet sea squirt,” Meade said.

Photographs of the ascidians will be sent away for identification, but they are most likely native."