Broad Bay celebrates a clean sweep

Environment Southland is celebrating a significant biosecurity milestone with the successful eradication of the invasive seaweed Undaria pinnatifida (Undaria) from Broad Bay, Rakiura/Stewart Island.

In September 2020, a single craypot in Broad Bay was found to have Undaria. Immediate removal and treatment followed, and extensive follow-up surveillance conducted from 2023 to 2025 found no further evidence of the pest in the area.

Environment Southland Marine Biosecurity Team Leader Kathryn McLachlan said the absence of Undaria during recent dive surveys confirms the prompt response was highly effective.

“Undaria is a rapidly growing seaweed that disrupts marine ecosystems. Its removal after initial detection shows that eradication can be achieved with swift, coordinated efforts”.

“We can celebrate Broad Bay’s return to Undaria-free status. This result demonstrates what can be achieved when regional authorities, local communities, and marine users work together,” Kathryn McLachlan said.

Ongoing vigilance is essential to prevent reintroduction and ensure permanent eradication and we will continue annual surveillance of both Broad Bay and the wider southern Rakiura area, including northern Rakiura and Easy Harbour, where the seaweed is still established, Kathryn McLachlan added.

“We want people to take steps not to transport Undariawhen moving around Rakiura, especially from the northern parts of the island, where Undaria is established. Remember to maintain a clean hull, and clean gear.”

The ocean is a vital part of our way of life. It’s a place for recreation, gathering kai (food), and connecting with nature. However, this marine environment is under serious threat from invasive marine pests, which can damage ecosystems, fisheries, and biodiversity.

The Protect Our Paradise campaign was born out of a desire to promote how to protect our precious marine environment.

As part of the campaign, this summer Environment Southland and Biosecurity New Zealand have partnered to employ a marine biosecurity ambassador for Southland. Ambassador John Carter, of Te Anau, will be out and about at boat ramps, wharfs and marine events to discuss the importance of marine biosecurity for the region.

New Undaria sites can be reported to Environment Southland through www.pesthub.es.govt.nz. Members of the public should also remember to leave marine pests in place and not try to remove them themselves.

For more information phone 0800 76 88 45 or email communications@es.govt.nz