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Hawksbill turtle on Milman Island - ©Veronica Joseph / WWF-Australia

Hawksbill turtle on Milman Island - ©Veronica Joseph / WWF-Australia

Made in the shade: How WWF is helping turtle populations

10 Feb 2019

Keywords
  • hawksbill turtles
  • marine turtles

Chris Hof

Marine Species Project Manager

 

I’ve worked with sea turtles for more than six years now and have always been captivated by these majestic ancient mariners. The first time I worked with sea turtles was in 2013, and I was sold. With their complex life cycle spanning many beaches and ocean basins, turtles showcase what it means to be truly connected to land and to sea, and how important it is to conserve and protect our oceans. Marine turtles may have been present in the ocean since the time of dinosaurs, but they’re now under threat.


Climate change is impacting turtles
Climate change is a major issue. It’s a bowling ball rolling toward us. As a result, we’re seeing warmer temperatures not only in the sea but also on sand and land.

Every year female sea turtles return near to the beach where they hatched to dig a nest deep in the sand to lay their eggs. Although they return to the sea, their eggs stay hidden for about two months, slowly incubating in the sand.

Rising sand temperatures are of particular importance when it comes to sea turtles. This is because the sex of the turtle is determined by the temperature of the sand around the eggs. Temperatures above 29.1°C generate mostly females, while temperatures below this are male. Sand temperatures above 34°C are considered fatal for the turtles growing inside.

As part of the WWF Rivers to Reef to Turtles study, scientists from the National Oceanic and Atmospheric Administration (NOAA) trialled a new method to determine the sex of juvenile and subadult green turtles foraging grounds in the northern Great Barrier Reef. We found that over 99% of the northern Great Barrier Reef stock were females - meaning virtually no males are now being born. This is known as feminisation. And it is detrimental to the future of sea turtles.

Last month, I travelled to Milman Island, a nesting site for hawksbill and green turtles, 140 km from the Cape of York (a few hours by boat north of the very tip of Australia). Here our researchers were at the beginning of a new project that’s looking into ways to combat this feminisation trend.

The picturesque Milman Island offers ideal conditions to trial a series of shade structures that aim to cool sand temperatures. Milman Island used to be one of the world’s largest hawksbill nesting sites and is also home to the northern Great Barrier Reef green sea turtle. These green turtles are the stock proven to be feminising and have been doing so for decades.

 

Milman Island

Milman Island, the site of the trial, is located off the coast of Far North Queensland © Melissa Staines

 

The solution is shade

Working together with the University of Queensland, the Queensland Government and supported by furniture company Koala, we’re investigating simple but effective ways to cool sand temperatures and re-establish more natural gender numbers of offspring - ultimately saving the species.

For the project, some green and hawksbill turtle nests will be left in direct sunlight; others will be sheltered with a shade cloth structure; others with natural options of dropped or washed up palm or pandanus leaves and some will be irrigated with seawater. Nests built under natural tree shade will also be monitored. A data logger will be placed in the relocated nests to keep track of temperatures.

In order to do this, we need to be on the island when turtles are nesting to relocate eggs for the cooling tests, and stay until they hatch. This means three months of research and many volunteers. With other competing projects, unfortunately my first visit to Milman Island this year was limited. I was able to help the research team monitor the beach for nesting turtles, build the palm frond shade structure and water the nests. In particularly, I eagerly await the results from the seawater trials. Each night, I helped with the task of pouring eight litres of seawater onto the nests. Seawater as well as dropped palm fronds are readily available across the Western Pacific region - in areas where we are concerned feminisation may also be occurring. If these methods are proven to be successful, they cost nothing. It might just be the most suitable option for shading turtle nests in remote areas. For Raine Island, the largest green turtle rookery in the world, seawater trials may prove to be the best management response to the feminisation trend, and set the way for trials on a much larger scale.

The life of a researcher - even on an island as beautiful as Milman - isn’t as glamorous as it might seem and is far from a 9-5 job. We patrol the beaches for nesting turtles during the night (and depending on tides, this can almost be all hours of the night). Outside those hours, we’re on turtle watch among other tasks, like marine debris clean up, from early morning and throughout the day as temperatures soar up to 38°C and sometimes reaches 90% humidity. Undoubtedly, the heat of the sand climbed too, but safeguarding the future of sea turtles is worth putting up with the heat, humidity and lack of sleep. 

 

Irrigation of turtle nests with sea water

Chris Hof and Project Lead, Melissa Staines irrigate sea turtle nests © WWF-Australia - Veronica Joseph

What’s next?

I’ll be returning to visit our research team in March when the turtles will start to hatch. We’ll retrieve the data loggers to find out how the cooling tests changed the sand incubation temperatures and sex of the hatchlings.

Once the turtles hatch our scientists will conduct quick ‘performance tests’ to see how fast the hatchlings can crawl, swim, and flip over if they are on their backs. Hatchlings need peak performance when they break the sand to get to the water before they’re eaten by circling predators above and below the water.

Our researchers predict the shaded nests will produce more energetic hatchlings than sun-exposed nests because locomotion performance is impeded by high nest temperatures. We hope this means the shaded nests will have the best chance of survival. 

 

Hawksbill hatchling in Milman Island

A hawksbill hatchling emerges from its nest © WWF-Australia - Veronica Joseph

 

The long game
If climate change isn’t addressed we’re going to see complete feminisation of the northern Great Barrier Reef green turtle population. This is detrimental to the longevity of the species. It’s projects like these that are trying to combat this issue to reduce sand temperatures so we can produce more natural sex numbers and hopefully recover the populations.

To safeguard the future of these majestic mariners we also need to address the raft of other threats that green and hawksbill turtles face. This includes poaching, fishing by-catch and loss of habitat. WWF-Australia is already working in partnership to reduce these threats, and you can support us.

Learn more about the turtle cooling project

Donate today and become an Ocean Protector. 

 

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