A groundbreaking international study of leatherback turtle populations off the Bay of Plenty coast has wrapped up in Whakatāne.

The project saw scientists from America and Australia work alongside New Zealand researchers to conduct aerial surveys of Bay of Plenty waters off Whitianga and East Cape, looking for leatherback turtles.

The research is the first of its kind in New Zealand, where not much is known about the local turtle population.

The Department of Conservation is leading the local study alongside world leaders Upwell Turtles, with support and expertise from NIWA, Monash University and Moss Landing Marine Laboratories.

DoC senior marine science advisor Karen Middlemiss said it was the first independent research being done in New Zealand into the turtles, with estimates otherwise coming from the fishing industry’s bycatch data.

The study was run by DoC’s bycatch and threats team, which focuses primarily on the impacts of commercial fishing on protected species.

They wanted to look at the abundance of leatherback turtles in the Bay of Plenty, which Dr Middlemiss said was the region where most of their interactions with commercial fisheries occurred.

It was funded through the Conservation Services Programme, with half paid by the Crown and the other half by fisheries levies.

In addition to where and how many leatherbacks are in the region, Dr Middlemiss said they wanted to discover how effective the aerial survey method was for potential future studies.

She said while many human interactions with the turtles were because of bycatch by fishermen, it was not intentional.

“I have been to the port and talked to fishers. They love the turtles, they don’t want to catch them, and they want to work with us to work out how not to catch them.

“They enjoy seeing them out there swimming around in the ocean as much as anybody else. We're all working together.”

NIWA principal scientist – fisheries Matt Dunn said researchers knew for a long time that the leatherbacks existed in New Zealand waters because of bycatch data, but it was not known until recently how many there were.

He said there was a spike in the number of interactions between the turtles and fisheries in 2021, which is when they started to understand the scale.

But Dr Dunn is clear that not all turtles caught in bycatch die, and many are released without issue.

“The issue is to find out where we’re interacting with them most, then if that actually presents a substantive problem – if the animals are released and are fine, or not – and then what we can do to reduce the number of interactions or the negative effects of those interactions.

“It's a management issue to determine what to do about it, and that’s not our concern. Our concern is to tell them where the animals are, what they’re doing, how they seem to be using habitats and how they might be interacting with the fisheries that are out there.”

Leatherback turtles are highly migratory and are found foraging in New Zealand waters in summer months, arriving in November and leaving in April.

George Shillinger, Upwell Turtles executive director, said leatherbacks are among the most highly migratory and transboundary marine species on the planet.

“Effective conservation requires international collaboration from nesting beaches all the way to distant foraging habitats,” he said.

“We are thrilled to have New Zealand contributing to our global understanding and conservation of this ancient turtle species.”

They also travel to Australia, Monash University research fellow Sean Williamson said.

“We're probably 20 years or more behind the US in terms of understanding their use of the habitat.

“But if you look back historically through records, it’s obvious they’ve been here for a long time; it’s us biologists that have taken a bit more time to really register that it’s a proper foraging ground.”

Dr Williamson said they were interested in replicating the study in Australia, too.

An international approach is required to protect the dwindling population because they forage and nest in waters across the Pacific Ocean, crossing the boundaries of several countries.

The Bay of Plenty aerial surveys took place over two weeks, concluding on Sunday, with scientists flying at low altitude.

They did so in a specialised plane, which was already available in New Zealand, with bubble windows that allowed them to view the water at a 90-degree angle.

They could only fly on days with optimum weather conditions.

Karin Forney of Moss Landing Marine Laboratories said although the leatherbacks were large animals at up to two metres long and 600 kilograms in weight, they were very small dots in the ocean when viewed from a plane 650 feet in the air.

“We need to have very calm weather and sunny skies to get the light that allows us to see into the water.

“This time in March was the trade-off between being here in the leatherback season and finding a time period that tends to have acceptable weather patterns.”

It took a specific skillset to be able to identify marine life from the air, and training was given to those going in the plane.

The plane comprised two rows of observers and one person recording data, in addition to two pilots who were comfortable – and skilled – at flying low and slow.

Dr Forney said Sarah Dwyer, of the DoC Aotea Operations Team, was particularly important to have on the plane because she was familiar with New Zealand waters.

“Waters especially here in the Bay of Plenty are a little bit warmer and more tropical, so you get warmer water species than we tend to get on the US West Coast.

“Sarah has been really great helping us figure out some of the species we don’t get.”

While the researchers were in the air, they logged every marine mammal they saw, not only the leatherback turtles.

Upwell Turtles research project technician Sierra Fullmer said the range of marine life they saw in Bay of Plenty waters was “striking.”

They saw beaked whales, baleen whales, ocean sunfish, and many different dolphins and toothed whales.

“The variety of species that you have has been pretty spectacular from my perspective.”

They took requests from other agencies who were interested in incidental data that may be collected on marine life like manta rays.

Moss Landing Marine Laboratories research associate Scott Benson has been leading leatherback turtle research on the West Coast of the United States since 2002.

He said this time of year was when fisheries had reported the highest number of interactions with the turtles in New Zealand.

They feed on jellyfish and are unique among turtles because they can maintain a body temperature greater than their environment.

“But when the jelly aggregation or density becomes lower, seasonally, then they move up to the tropics where the waters are a little warmer.

“They go back and forth between here and the Kermadecs until they are ready to go back to their nesting beaches in the Solomon Islands or Papua New Guinea or Indonesia, which they do about every two to three years.”

Mr Benson said the United States considered the leatherback turtle to be critically endangered, with numbers having declined 80 per cent in the last 30 years.

The figures have come from analysis of data gathered both from nesting beaches on Pacific Island countries and an index foraging area near California.

Mr Benson said there was a high likelihood that the leatherback turtles would become extinct in the next 30 years.

“They are caught in fishing operations and there are some issues still at some of the nesting beaches with harvesting of eggs and harvesting of adults, although less than there used to be.

“We recognise that affording protections to them off the west coast of the United States isn’t going to be anywhere close to being enough, because these are trans-boundary species that range across the whole Pacific.”

Mr Benson said they were looking for partnerships across the Pacific and were happy to have that now with New Zealand.

The public can contribute to protecting leatherbacks and other marine animals by preventing plastics and pollution reaching the sea.

No marine turtles nest on beaches in New Zealand, any turtle on the beach should be reported immediately to 0800 DOC HOT (0800 362 468).