A single juvenile plant of the invasive seaweed Undaria has been pulled from a mooring line in the far south of Rakiura after a fisherman noticed something unusual and reported it.
The plant was found attached to a line near Pukeweka Island, off Taukihepa/Big South Cape Island at the southern tip of Stewart Island/Rakiura. Environment Southland investigated the report, removed the plant and sent specialist divers to search the surrounding area. They found no further sign of the pest.
Environment Southland marine team leader Kathryn McLachlan said the speed of the report made the difference, allowing the council to respond immediately and check whether a wider infestation had taken hold.
"We're incredibly grateful to the fisherman who reported what they found," she said.
Undaria pinnatifida is an Asian kelp that can spread quickly, compete with native species and change the make-up of marine ecosystems. It is already established in parts of Southland and remains one of the region's most significant marine biosecurity risks. Divers carried out an Undaria survey around Rakiura in 2023.
Eyes on the water
Ms McLachlan said people who spent their time on the water were often the first to notice changes in the marine environment, and boaties, fishers and other water users played a key role in protecting Murihiku Southland's coast.
Early detection, she said, was one of the most effective tools available for managing marine pests, and the council would always rather investigate a report and find nothing than miss a new arrival.
She described the outcome as "a great example of biosecurity working exactly as it should".
Environment Southland will keep monitoring the area through its future surveillance work. It is asking anyone who finds a suspected marine pest, or notices anything unusual in the marine environment, to report it promptly.
Island already under the biosecurity spotlight
The find comes at a time when attention on Rakiura's biosecurity is already high on land. The Predator Free Rakiura programme, led by the Department of Conservation, Te Rūnanga o Ngāi Tahu and Zero Invasive Predators with input from the island community, is working towards removing rats, possums, feral cats and hedgehogs from the island, while Te Puka Rakiura Trust is developing a biosecurity system designed to stop those predators returning once they are gone.
The marine side of that picture depends heavily on the people who work the waters around the island. In this case a quick phone call, a dive team and a single plant in a bag appear to have been enough to head off a problem that, left alone, could have been far harder to reverse.
