Conservation Comment: Red-eared sliders breeding at Virginia Lake

Red-eared sliders at Virginia Lake, September 2021. Photo / Ormond Torr

Cute baby turtles bought from pet shops have matured and later escaped from backyards or been illegally liberated when they have outgrown their enclosures.

Biosecurity staff in some regional councils are concerned that too many of these exotic animals are out in the wild. They have been found from Northland to Southland.

The red-eared slider Trachemys scripta elegans is on the world's 100 worst invasive species list (compiled by the World Conservation Union's [IUCN] Invasive Species Specialist Group). The terrapin has an olive to brown carapace patterned with yellow spots or stripes and a distinctive red stripe behind the eyes.

Their omnivorous diet includes all plant parts, molluscs, frogs, crustaceans, insects, gastropods, birds and small reptiles.

They can grow up to the size of a dinner plate, live for 40 years and require great effort to look after in a tank.

Whanganui resident Margie Chiet found a female red-eared slider crossing London St near Whanganui Collegiate before Christmas last year. She took it home where it was a hit with her grandchildren for several weeks.

Her friend Jo McDonnell has kept three female turtles in a secure enclosure for years. Margie's find was added to that group.

At Cooks Beach on the Coromandel Peninsula, a volunteer set up a homemade basking trap to catch turtles inhabiting an artificial lake.

Volunteers check the trap daily and have caught 12 turtles so far. A female turtle still carrying eggs was removed from the wild before laying her eggs.

It was originally thought the species could not reproduce in the wild in New Zealand due to our cooler climate.

Captured turtles are being housed at the University of Waikato; help with research into this species involves developing eDNA detection and isotope analysis to determine feeding habits.

Whanganui wildlife photographer Ormond Torr says his first photos of a turtle were taken at Virginia Lake in January 2010.

University of Waikato biological scientist Nick Ling says, "The species seems to have been in the lake for at least 20 years.

"A female turtle there has been seen laying eggs. They have also been caught in the Whanganui River."

Mr Ling says global warming was likely the cause of breeding populations in New Zealand. He predicts that within 10 years, more female turtle offspring will hatch as – like many reptiles – the temperature determines the sex.

"Between 20 and 27 degrees, every egg is going to be male, and above 31 degrees females are produced.

"The 'Goldilocks' temperature is 28.5 degrees, where either sex can be hatched.

"We monitored the temperatures at Cooks Beach and it was hovering a couple of degrees below the Goldilocks temperature."

Sexual maturity appears to be size-related, with males maturing when their carapace length is about 10cm and that of females 17cm. Females can retain sperm and produce offspring up to five years after insemination.

They can produce two or three clutches per season. The egg number per clutch varies, generally in the range of four to 15, but as many as 23 per nest have been recorded in South Africa.

Auckland Council has made a ruling: you may not breed, distribute or sell any red-eared slider or other sub-species of Trachemys scripta within the Auckland region from September 1.

If you have a pet turtle, ensure it is securely contained to avoid accidental escapes. If you cannot look after it, find someone who is prepared to give it a lifetime home, or contact a pet shop or animal rescue organisation to get the animal rehomed.

Never release a red-eared slider into the wild. It may be unable to find the food and shelter it needs, and it also puts New Zealand native species at risk.

The red-eared slider originates in southern USA and Mexico. It is called a slider due to the fast way it slides into the water when startled.