Red-eared slider turtles have been called one of the world's 100 worst invasive species. Photo: Laszlo Ilyes / Creative Commons
Authorities are concerned for native freshwater plants and animals as introduced wild turtles begin looking for food in spring.
The global Invasive Species Specialist Group classified red-eared slider turtles as one of the world's 100 worst invasive species more than 20 years ago.
Department of Conservation (DOC) freshwater ranger Matt Brady said red-eared slider turtles are sluggish over winter and enter a brumate state where they do not eat for weeks.
"Brumation is like a half hibernation. When red-eared sliders emerge in spring, looking for food, they're a serious threat to native freshwater plants and animals."
Brady said the turtles would eat fish, plants, aquatic insects, koura and small birds including ducklings.
Auckland has banned the breeding, distribution and sale of the turtles, but they can still be easily bought and keep as pets in other parts of the country.
Brady asked anyone considering buying a red-eared slider turtle to do their "due diligence".
"Red-eared sliders can grow to the size of a dinner plate and live for up to 50 years. They have particular habitat needs such as large, heated aquarium or a secure outdoor pond. Taking on a turtle requires 100 percent commitment."
As climate change brings increased temperatures, there is also concern that both male and female young will hatch and allow a self-sustaining population to establish in the wild.
There was already evidence red-eared slider turtles were now able to multiply in the wild in the Waikato region after a population in the Coromandel was found to be breeding in 2015.
Volunteer leader Jayne Nightingale and a team of volunteers have caught 76 red-eared slider turtles at Cook's Beach in Coromandel since 2021. These include turtles caught in a trap provided by Waikato Regional Council as well as those handed in by the community or as bycatch in fishing gear.
"When I first started trapping turtles, I was met with a lot of negativity from the locals. However, with a bit of education, the ecological impacts from invasive turtles have become much better understood.
"The trapping work has been so successful that we think only a couple of the turtles remain at large. We hope to catch them this spring, when they're more active."
New Zealand does not have native freshwater turtles, so any turtle seen in the wild is an escaped exotic species.
DOC is asking people to report any wild turtle sighting on iNaturalist or the Find-A-Pest app.
"This helps DOC and regional councils to understand where the turtles are, how many there are, and it informs how we manage them," Brady said.