Simple intervention could help stabilise turtle populations – research

Tess de la Mare, PA
·4-min read

A simple intervention to cool turtle nests could help stave off a growing crisis in the sex ratios of global turtle populations caused by climate change, newly published research has found.

The sex of turtle hatchlings is determined by the temperature at which the eggs incubate, and as global temperatures rise vastly more females than males are hatching, putting their future in jeopardy.

Many turtle populations are now showing evidence of a female sex bias, the green turtles in particular are facing disaster with 99% of all eggs in some regions hatching female.

But research among loggerhead turtles on the island of Boa Vista, part of the Cape Verde archipelago off the west coast of Africa, has found that a cheap intervention to cool nests could be a means of stabilising populations.

The study found that in natural nests on the island 69% of all hatchlings are female, with this figure expected to rise to up to 95% in the coming years as global warming impacts the temperature of the sand.

There were an average of 92 eggs in a loggerhead turtle clutch, the research found.

But by halving the number of eggs in a clutch scientists found they could lower nest temperatures by reducing the amount of metabolic heat, the heat generated by the hatchlings developing, by 0.5C, resulting in just 45% female hatchlings.

Shading the nests, where dark fabric was suspended 15cm above the clutch, had an even more dramatic effect, reducing average temperatures by 1.1C and producing just 1.46% females on average.

Shaded nests
Shading nests had a dramatic impact on sex ratios (L Clarke and L Hawkes/PA)

Dr Leo Clarke, a marine biologist at the University of Bangor and lead author of the study, told the PA news agency: “Every night we would trek up and down the beach and there would be female turtles coming ashore to dig their nests and laying their eggs.”

He explained: “Once they begin to lay their eggs they are in a sort of catatonic state, a bit of a trance, and you can collect the eggs as they lay them.”

The eggs were transferred to a fenced-off hatchery on the beach run by a local conservation programme to protect them from predators such as birds and crabs.

A data logger placed in each nest, which were all buried to a depth of 45cm, recorded the temperature every 15 seconds throughout incubation.

Little plastic corrals were built around the nests to keep the hatchlings separate until the researchers had recorded their sex and the fitness of those in each clutch before releasing them into the ocean.

Turtle nests
Plastic netting kept the hatchlings from each nest separate (L Clarke and L Hawkes/PA)

Dr Clarke said: “Obviously we want to know when you are intervening like this whether it actually affects the hatchlings because temperature also affects their size and potentially fitness and could affect their long-term survival.

“Once they emerged from the nest we took various measurements from the hatchlings, size, weight, how fast they could run and how fast they could right themselves when they were on their back.

“Importantly we found that although there were differences in the sex ratios and in nest temperatures, there was no difference in the condition of the hatchlings.”

The researchers believe that the interventions could buy loggerhead turtles some time as world leaders try to limit global warming to 1.5C, and are optimistic the results can be reproduced in other turtle species.

Turtle hatchlings
The health of the baby turtles was not affected by the interventions (L Clarke and L Hawkes/PA)

Dr Clarke said: “There is variation between species and variations between populations, but for most species of turtle the number of eggs in a nest are high, sometimes up to 150 eggs in a clutch.

“Metabolic heat may be significant based on the number of eggs that are incubating so clutch splitting, we predict, would work elsewhere.”

There is also a huge amount of will in regions with turtle nesting sites, many of them in developing countries, to protect the populations as they are a massive draw for tourism.

“You find a lot of ex-turtle poachers are now employed in turtle watching and tourism activities,” Dr Clarke said.

“For almost every turtle population around the world there’s some sort of conservation effort going on with those populations.”

Turtles are also vital to regulating in-shore ecosystems.

“They are grazers and they keep the algal growth down on coral reefs,” Dr Clarke said.

“Coral reefs are finally balanced ecosystems and if you remove species that graze on algae what you will find is that you get huge growths of algae and the coral suffers as a result.”

The paper Low‐cost Tools Mitigate Climate Change During Reproduction In An Endangered Marine Ectotherm is published in the Journal Of Applied Ecology.

The research was conducted in 2012 and repeated in 2014.