Undaria survey yields positive results

Media Release

1 February 2023

An Environment Southland dive survey on the southern coast of Rakiura/Stewart Island has found no sign of the invasive seaweed in Broad Bay, where a previous incursion was identified in 2020.

Divers spent a week in early January survey where they surveyed Broad Bay, Easy Harbour and a number of key anchorages on the southern coast.

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

Environment Southland 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.”

Divers also completed a follow-up inspection of the incursion discovered in Broad Bay in 2020. At the time, Undaria was removed from craypots.

“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 aspect 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.”

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