Luke and Isla, as the juvenile turtles had been named, had been weak and underweight, and gut impactions, caused by ingesting plastic, when they were found, Kelly Tarlton's SEA LIFE Aquarium curator Andrew Christie said.
"These turtles are generally found in warmer tropical waters, but they can be washed on to our shores during colder periods if they are weak and suffering from injury or illness, and we do our utmost to assist them back to health," Mr Christie said.
"We're delighted to be growing what is a very successful partnership with Auckland Zoo. With the zoo's vet team and the expertise of Massey University researcher and marine turtle expert Dan Godoy, our aim is to further improve the specialist care we can give to ensure the successful release of these endangered marine mammals."
Kelly Tarlton's had treated more than 80 turtles since the inception of its rehabilitation programme, made possible with the support of the Kelly Tarlton's Marine Wildlife Trust. This was the third time that Far North turtles had been restored to health and released, but it had been a slow process.
Aged eight to 10 years, some 15 to 20 years short of reproductive age, they could grow from their current weight of 15 kilograms to well over 100 kilograms, with a similar lifespan to humans.
Both had been extremely fatigued and heavily encrusted with barnacles when they were found. Luke, the bigger of the two, had only needed warming up, antibiotics and a special diet, but Isla had needed two months of intensive care, including tube feeding, thanks to a blockage of the intestinal tract.
Both had eventually been transferred to Tarlton's main aquarium, where they had eaten a "huge amount of food once they came right."
"Many turtles brought to us have mistaken plastics and other rubbish for their staple food items, such as jellyfish and sponges," Mr Christie said.
"Once they have swallowed this rubbish the turtles remain buoyant and are unable to dive for food, which starts a process of starvation and a slow, agonising death.
"We can all help reduce the human impact on turtle habitats, starting by protecting our beaches and disposing of rubbish appropriately."
There was growing evidence, he added, that young turtles spent time growing up in Far North waters, and DNA samples had been taken from Luke and Isla for analysis in Australia, in the hope of establishing which part of the Pacific they had come from.
Both went back to the Tasman Sea carrying antennae that would send signals to a satellite every time they surfaced, recording their position, water depth and temperature.
