Conservationists are increasingly moving turtle nests out of harm’s way to protect them from rising tides and temperatures. We’re learning that there might be unintended consequences.
A turtle hatchling’s fate hinges on where its mother lays her eggs.
Too close to the tide line and the waves might wash them all away.
The further up the beach she lays her eggs means a longer journey to the water for her babies, all the while being dive bombed by hungry birds or dragged underground by waiting ghost crabs.
There’s a reason only about one in a thousand newly hatched turtles ever makes it to adulthood.
And temperature is an emerging threat that mother turtle perhaps didn’t consider when marking out her nest.
Because incubation temperature is a key determinant of hatchling sex and warmer temperatures mean more females, climate change means some clutches are over 90% female.
But when a nest is in trouble, it’s becoming increasingly common for conservationists to intervene and move it somewhere safer, higher up the beach above the tide line and covered by shade cloth to better regulate temperature.
“It’s generally reserved for ‘doomed’ nests,” says UNSW sea turtle ecologist Davey Dor.
“Nests laid too low on the beach or somewhere they’d likely be flooded, preyed on or overheated, or where the whole clutch would otherwise be lost might be moved.”
Nest relocation is widely used around the world, including in New South Wales where last year ahead of ex-Cyclone Alfred, authorities pulled off the state’s largest ever egg rescue.
Led by the National Parks and Wildlife Service and NSW TurtleWatch , wildlife carers and rehabilitation groups, relocated over 1,000 eggs from nine nests on the north coast before the swells hit, with hatching success as high as 96%.
But as nest relocation becomes more common, Mr Dor wants to know what else moving a nest does to the hatchlings.
In a recent study published in the journal Marine Biology , Mr Dor, along with Associate Professor Lisa Schwanz at UNSW and Dr David Booth at the University of Queensland, studied 48 green turtle clutches over two nesting seasons on Heron Island on the southern Great Barrier Reef.
Nests were randomly assigned to one of three groups: left where the mother laid them; relocated beneath 95% shade cloth; or relocated without artificial shade.
They measured temperature, hatching and emergence success, hatchling size, sex ratios and physical performance including crawling and the ability to flip themselves upright.
Physical performance is particularly important for a hatchling, which might have to crawl 50 metres from the nest to the relative safety of open water.
If a hatchling gets flipped over or turned around and can’t right itself, it’s easy game for predators.
On Heron Island, hatchlings that clear the beach also face a swim through predator-infested shallows, meaning baby turtles need every advantage they can get.
“That initial crawl down the beach is fraught with different obstacles and predators, so how quickly a hatchling makes it across can come down to both its size and speed,” says Mr Dor.
Mr Dor found that unshaded relocated nests were much hotter and produced overwhelmingly female hatchlings, with just 8% of those sampled in one season estimated to be male.
Shading brought nest temperatures down and the sampled sex ratio was much more balanced, at 55% male.
But the key concerning finding is that the relocated nests still had lower hatching success and produced hatchlings that were smaller and worse at righting themselves.
“The difference shows up even when the shaded and natural nests are the same temperature,” says Mr Dor.
“We can’t pin it to a single factor.”
Mr Dor says moving a clutch can change any number of things at once: the moisture around the eggs, the sand they develop in, how gases move through the nest, the microbes they develop with, and how deep they sit.
Any of these, alone or together, could be shaping how the hatchlings turn out.
“Our next step is to tease these factors apart.”
Mr Dor says the findings don’t mean conservationists should stop moving nests that would otherwise be doomed.
Instead, they show how important it is to understand the different factors that determine hatchling success, particularly as shifting climates and changing coastlines mean we may come to rely on it more and more.
“Nest relocation as a conservation strategy has been used all over the world for a long time now,” he says.
“We need to understand these factors so we can give the turtles we’re trying to save the best chance of survival.”
As for how this impacts the hatchlings over the course of their lives, Mr Dor says it’s impossible to say right now.
Once turtles make it to the water they enter what scientists call their “lost years”, and we might not hear from them until they return to our coastal waters as sub-adults in about 10-20 years.
“Sea turtle conservation and science is very much a long-term game,” says Mr Dor.
“Only very recently with satellite tracking have researchers started to really piece together what goes on during those lost years.”
But there is evidence that research and conservation are paying off.
Earlier this year, green turtles were reclassified from endangered to least concern on the IUCN red list, a huge moment for a species that was once on the path to extinction.
The focus for researchers and conservationists now is making sure the interventions designed to protect the next generation give them the best possible start.
