Red-eared slider turtle spotted at Whanganui's Virginia Lake

A red-eared slider turtle, spotted at Virginia Lake on Sunday. Photo / Colin Ogle

A red-eared turtle spotted at Whanganui's Virginia Lake could be an unwanted pet - but the species is also on a global list of invasive pests.

St Johns Hill resident Colin Ogle photographed the turtle on Sunday, and said he had seen the animals there quite often over the past few years but he didn't have any idea how many of them there were.

"I know they're classed as a pest, but whether there are enough to cause concern, I have no idea," Ogle said.

Department of Conservation Whanganui operations manager Tahinganui Hina said red-eared slider turtles were pets that occasionally "outlived their welcome".

"They are a long-lived species and are regularly dumped as unwanted pets," Hina said.

"They are unable to successfully breed in the wild under New Zealand conditions because temperatures determine the sex of offspring, and only males have been observed.

"Climate warming may see this change, and I would expect localised increases in populations at common dumping grounds."

Hina said red-eared sliders were listed in the top 100 in the Global invasive species database, as well as in several regional councils' pest management plans.

However, the turtles, native to southern parts of the United States, are not listed in Horizons Regional Council's pest management plan.

"They are omnivorous and feed on a range of vegetation and animals including molluscs, fish, insects, small birds and reptiles," Hina said.

"There is little pressure from natural predation in New Zealand, as adult turtles are about the size of a dinner plate."