The Department of Conservation has joined an international effort to protect endangered leatherback turtles.

This week DOC researchers are in the sky over the Bay of Plenty counting the turtles, which stop for a feed during a long migration.

"The leatherbacks are really an amazing species. They're as ancient as the dinosaurs," Department of Conservation senior science advisor Karen Middlemiss said.

"They make these really large migrations from the west coast of the states down to their breeding beaches in places like the Solomons, and on their way they're passing through our waters here and using them as important foraging grounds."

Like its name suggested, leatherback turtles had thick skin instead of a shell.

They travelled enormous distances, which meant keeping track of their behaviour was a team effort.

The project was a collaboration between the Department of Conservation, NIWA, Australia's Monash University, and American non-profit Upwell Turtles.

Upwell co-founder George Schillinger said it was essential to work on an international scale.

"It would be impossible to adequately protect leatherbacks without working collaboratively and internationally," he said.

"Our research has shown in previous studies that leatherbacks are among the most transboundary or highly migratory marine organisms on the planet."

He said the leatherback population had dropped drastically in recent years, pushing the ancient species to the brink of extinction.

"Leatherbacks are considered critically endangered in the Pacific, with the western Pacific turtles having experienced a greater than 80 percent decline in the last 30 years.

"[They are] facing potentially extirpation or removal from the Pacific by the turn of the century if we can't address the many threats."

Middlemiss said that, for the first time, researchers were counting turtles in New Zealand waters.

"So the teams basically fly transect lines backwards and forwards, and the trained observers on board are looking out down beneath them to spot these animals in the water," she explained.

"They're very large turtles so that makes them easier to see from the air."

Commercial fishing was one of the biggest threats facing leatherback turtles. Schillinger said the goal was to identify hot spots where the turtles gathered so fishing boats could avoid them.

"Well the hope is that the surveys will give us the basic data we need on turtle distribution and abundance and this can in turn then be used and applied by government agencies and fishers to reduce this overlap and to reduce interactions," he said.

"Hopefully that in turn will have a positive impact on this population."

Seafood NZ's Tiffany Bock said the commercial fishing industry was keen to see the results.

"Fishers are out there in the marine environment every day and mostly because they love it so to them you know having a functional and biodiverse marine ecosystem is a big deal and they're really keen to avoid any sort of negative impacts on that," she said.

"I mean obviously any work to better understand turtles and where they go in the marine environment is a positive one."

The research was funded through DOC's conservation services program which took levies from commercial fisheries.

-RNZ