Conservation areas undershoot range of endangered Australian sea turtles

December 14, 2020

A green sea turtle at Australia's Cairns Aquarium. (David Clode, Unsplash)

Endangered green sea turtles were found in new research to roam far outside the boundaries of existing conservation areas in Australia, putting them at risk of falling victim to boat propellers and other harmful interactions with humans. 

The study published this month was part of a program at the Australian Institute of Marine Science that aims to help government, industry and communities make informed decisions about the marine ecosystem in Australia and particularly on its Northwest Shelf, home to one of three genetically distinct green turtle stocks in Western Australian waters.

Researchers found that existing conservation areas largely underestimate the space the turtles use for foraging, migrating and other activities. Understanding the range of the turtles is of growing importance amid increasing hydrocarbon and mineral resource development in coastal areas, which could pose grave dangers for the turtles. 

The scientists also were interested in limiting potential damaging interactions with humans, for example from the use of artificial light at night, which can disrupt breeding.

“We know very well where green turtles nest in Australia, but we didn’t know where they went once they left those nesting areas,” said Luciana Ferreira, a postdoctoral scientist at AIMS and lead author of the research’s resulting paper, which was published Dec. 4 in Diversity and Distributions

The researchers analyzed data from 76 turtles tagged in previous studies that hadn’t been analyzed on a regional scale, and also tagged 20 more females nesting at beaches in Western Australia, tracking them with satellites. 

“The Western Australia stock is distributed along the whole northwest of Australia,” Ferreira said. “We really needed to have a large-scale view of where these turtles are going.”

The result was the mapping of newly discovered foraging grounds as well as migratory routes utilized by the green turtles, whose national conservation status is considered vulnerable by the Australian government, and which are listed as endangered by the International Union for Conservation of Nature.

In particular, while turtles are present during the breeding season in inter-nesting areas that are covered by protections, when it comes to foraging, Australia’s spatially defined “biologically important areas” are “largely underestimating” the space being used by turtles, according to the paper. 

The so-called BIAs aim to assist decision-making regarding regionally significant marine species with data on where they are known to do things such as breed, forage, rest or migrate, but “are often based on limited information and reliance on expert elicitation where peer‐reviewed published literature are unavailable,” the authors said.

Whereas green turtles in other parts of the world can cross oceans — and economic zones where other countries have jurisdiction over natural resources — to reach their foraging areas, the animals in the study largely remained within Australian coastal waters, although a small proportion migrated north to Indonesia. The researchers also identified two common migratory corridors for green turtles.

The findings help to understand the turtles in the context of the Australian coastal shelf, and suggest this sub-population of turtles needs a form of management focused more on that country, Ferreira said.

Because much of the data analyzed came from individual studies with differing objectives, and a lot was contained in unpublished reports, when officials developed the current protections for turtles, a lot of the information was not available.

“The ultimate goal was to provide robust data, and the data in a format the managers can use,” Ferreira said. “What they’ll decide to do, it’s up to them, but we showed how the foraging distance of turtles is much larger than the area that is currently being protected, so maybe in the future the data we provide can help them refine those biologically protected areas.”

The researchers were able to construct a much more accurate distribution map by expanding their dataset through collaboration with industry and turtle scientists in Western Australia, including that government’s Department of Biodiversity, Conservation and Attractions.

But they noted that because the study showed “relatively low” overlap among foraging turtles, it may suggest the inshore waters of much of northern Australia are flush with available foraging habitat.

“However, our analysis indicated that despite our large sample size, it was still insufficient for calculating the total distribution over our large study area,” researchers said in the paper. “This is likely because our sample size is still considerably small when compared to the expected population size of green turtles in Western Australia.”

The Northwest Shelf stock counts about 125,000 turtles among its ranks, according to previous research.

In addition to signaling a healthy reef, turtles are adored by Australians and also hold special cultural and social importance to indigenous communities there.

“Turtles are iconic for anyone related to the sea,” Ferreira said. “We were really driven by that iconic importance of the green turtles to try and do the study and try to help Australia and the managers to protect this species.”

The paper, Multiple satellite tracking datasets inform green turtle conservation at a regional scale, was published Dec. 4 in 
Diversity and Distributions. The authors of the paper were Luciana C. Ferreira, Michele Thums, Sabrina Fossette, Phillipa Wilson, Takahiro Shimada, Anton D. Tucker, Kellie Pendoley, Dave Waayers, Michael L. Guinea, Graham Loewenthal, Joanne King, Marissa Speirs, Dani Rob, and Scott D. Whiting. The lead author was Luciana C. Ferreira.

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