Warm conditions could cause higher female turtle population

A new study by Swansea University academics has revealed that warmer temperatures associated with climate change may lead to higher numbers of female sea turtles which could result in the population collapsing in some areas of the world.

Hawksbill turtle 2The new study carried out by researchers from the University’s College of Science and Deakin University, Australia and published this week in the Journal of Experimental Marine Biology and Ecology‌ looked at the impact of warming temperature on three populations of sea turtles nesting in Zeelandia Beach at the St Eustatius National Park (STENAPA) in St Eustatius in the Dutch Caribbean. The majority of hatchlings born on Zeelandia beach had been female biased during the past decades.

Swansea University researcher Nicole Esteban, a former STENAPA Manager, said: “Sea turtles do not have sex chromosomes and it is the incubation temperature in sand surrounding a clutch of eggs that determines the sex of a turtle hatchling which is known as Temperature-Dependent Sex Determination. Eggs incubating at cooler temperatures (generally lower than 29 °C) produce male turtles and eggs incubating at warmer temperatures produce females. This has led to concerns that in the context of climate change, warming air temperatures may lead to female-biased sea turtle populations.”

The researchers recorded the sand temperature using small temperature loggers buried at turtle nesting depths on Zeelandia Beach between 2011 and 2013 where leatherback, hawksbill, and green sea turtles nest. The data was combined with temperature projections from the Intergovernmental Panel on Climate Change (IPCC) to model how sand temperatures will change on the beach in the next 100 years.

The results of the study showed that incubation temperatures are relatively high, averaging 31.0 °C, and ranging from 29.1 °C to 33.3 °C through the nesting season. Of the population of hatchlings for each species, the percentage of male hatchlings at Zeelandia Beach, were at the following levels:

  • Hawksbill males were at 36%
  • Leatherback males accounted for 24%
  • Green turtles males were less than 16%

Hawksbill turtleProjecting this information into the future suggests that the female- skew will be intensified by warmer air temperatures in the coming decades and there are indications that by 2090 less than 1% of green turtle hatchlings will be male.

Ms Esteban (pictured left diving with a Hawksbill turtle) said: “There is a real concern that there will not be enough males born on Zeelandia beach in the future. If there are too few males, the local population is at risk of collapsing. Another concern is that turtle eggs do not develop above a certain temperature. The study highlights the extinction risks of climate change to species whose biology is closely linked to temperature.

“This research underlines that there is real need for effective conservation measures to be put in place to prevent the localised extinction of these turtle populations in St Eustatius. Potential conservation strategies include shading turtle nests on the beach or moving nests to a cooler section of a beach such as a protected hatchery. The Marine Park Manager Jessica Berkel has reported they have already trialled relocation of turtle eggs to a cooler ‘hatchery site’ and this may well be one of the strategies used in future.”

‌"Sand temperatures for nesting sea turtles in the Caribbean: implications for hatchling sex ratios in the face of climate change” was published by the Journal of Experimental Marine Biology and Ecology (2015). Authors: Jacques-Olivier Laloë, Nicole Esteban, Jessica Berkel and Graeme Hays.

Read the study here

Pictures of Hawksbill turtles courtesy of Frogfish Photography


Story by Delyth Purchase