MARINE REPTILES ON THE EDGE

They’ve been on our planet since the dinosaurs, but sea turtles are now on the brink of extinction.

By Hannah Rudd.

When you think of sea turtles many of us conjure up images of turquoise blue waters and pristine sandy beaches, where these marine reptiles spend their days grazing on coral reefs. A scene in a certain Pixar film may also spring to mind. But turtles aren’t confined to the tropical waters of warmer seas, they can also make appearances in our much cooler seas.

We are continually learning more about these impressive animals, unveiling their secrets and gaining a deeper understanding about their life histories. These marine reptiles have wandered our oceans for the last 100 million years. Palaeontologists believe marine turtles appeared during the Jurassic period, but it wasn’t until the Cretaceous period 100 million years ago that prehistoric turtles began to evolve into what we know as sea turtles today.

Sea turtles have evolved to play a vital role in keeping our marine ecosystems healthy by grazing on seagrasses, algaes, corals, jellyfish and much more – depending on the species. This keeps these habitats more productive – similar to how we mow our lawns to keep them healthy – and ensures prey populations don’t explode, having huge consequences for ecosystem health.

Scientists are still not clear exactly how long sea turtles live, but it’s estimated that they have similar lifespans to us, living 50 years or more. Most species take between 20 and 30 years to mature and are only actively reproductive for around a decade. Every year millions of sea turtles head back to the very beach where they were born to lay their eggs and give life to the next generation of their species by using the Earth’s magnetic field. After (slowly) hurling themselves up the beach, a single female can lay between two and six clutches of eggs, each containing 65 to 180 eggs. There is a two-week gap between each clutch being laid and it can be up to nine years before she will experience another nesting season. Hatching sea turtles is a familiar sight on natural history documentaries as they scamper toward the big blue, trying to avoid being picked off by awaiting predators. But what happens from the moment these hatchlings enter the water to when they return to coastal shallow waters to forage –sometimes up to 20 years later – remains largely a mystery to us.

Worldwide there are just seven species of sea turtle. Here in the UK domestic waters we have recorded six of these species – most of which don’t belong in our seas at all and are the victim of stranding events. The ginormous leatherback (Dermochelys coriacea) is the most reliably encountered sea turtle here. During the summer months these impressive turtles migrate to our waters to feed on jellyfish. In fact, while not in the UK, the longest known record migration of a sea turtle is for a female leatherback who swam nearly 13,000 miles over 647 days from Indonesia to the west coast of America - over 20 miles a day! Our leatherbacks likely begin life at one of the many breeding colonies found in UK Overseas Territories – from French Guiana to the British Virgin Islands.

On the Brink

Tragically, in this day and age when you think of sea turtles you may also think of them munching on deadly plastic. Researchers estimate that more than 50% of sea turtles have ingested plastic –often mistaking it for their favourite food, jellyfish – and becoming entangled in plastic fishing nets also has suffocating consequences for these animals. When washed up on beaches plastic can also make nesting difficult as the giant females desperately try to hurl themselves up on the beaches. If she is successful in finding a spot to nest, many weeks later the tiny hatchlings may find it difficult to emerge from their nest if plastic is blocking their path.

Uncontrolled coastal development and vehicles on beaches are also problematic for nesting sea turtles. This disturbance can make it difficult for them to feel comfortable to nest and both light and noise pollution can deter them from being successful – wasting precious energy and time. Coastal development also can lead to pollution and sedimentation of inshore waters, degrading precious turtle feeding grounds like coral reefs and seagrass beds making them less productive.

Wand land runoff threaten the future of sea turtle’s favourite feeding spots, but climate change is putting further pressure on these habitats. 50% of the world’s coral reefs have been lost, primarily due to climate change and ocean acidification, and at the current rate of warming are at risk of being lost completely by 2050. Climate change is also challenging for sea turtle populations. Whilst incubating turtle eggs the temperature of the sand dictates what sex the emerging hatchling will be. As sand temperatures rise with climate change there is a risk that sea turtle populations will be skewed with more females than males making proliferating the future generations difficult. Rising seas also threaten to flood nesting sites and increased severity in storms may have impacts on hatchling survival.

Poaching and hunting continue to be threats for sea turtles too. Their eggs are considered a delicacy in many cultures and trade of turtle parts on the black market continues to be a profitable business. In West Africa, turtles are killed for use in medicine and traditional ceremonies, endangering their survival in the region. Their meat and shells are often the driving force behind their intentional capture in other