If you’ve ever dived or snorkelled on the Great Barrier Reef and seen a turtle majestically gliding by, then chances are it was a green turtle. It’s the most recognisable of all marine turtles and widely distributed throughout the world’s tropical and subtropical waters. Large populations live, feed and nest on the Reef, favouring the bays and protected shores near the coast and around islands. The green turtle is one of the largest and the only herbivorous marine turtle – feeding almost exclusively on seagrass and algae. Like other sea turtles, it migrates long distances between feeding grounds and nesting beaches, with females returning to the very same beach on which they were hatched to lay their eggs. Female green turtles have been tracked across 2,600 kilometres during such a migration. Producing the next generation of turtles is a lengthy process. Green turtles take 30-50 years to reach sexual maturity, after which females will only nest every 5-8 years. Although clutches may contain as many as 120 eggs, it’s estimated that as few as 1 in 1,000 hatchlings survive to adulthood.
Marine turtles have roamed the world’s oceans for more than 100 million years, and are an integral part of our tropical coastal ecosystems. It’s taken humans just 200 years to tip the scales against their survival and these ancient mariners are now considered endangered or vulnerable. Only a few large nesting populations of green turtles remain in the world and Australia has some of the largest. Raine Island, in the northern Great Barrier Reef, is home to the world’s largest green turtle rookery, with an annual nesting population of tens of thousands of females. In the southern Great Barrier Reef, a genetically distinct group of green turtles nest in the Capricorn/Bunker group of islands, numbering some 8,000 females. The continued health of green turtle populations has a large bearing on the overall health of seagrass communities. Turtle grazing helps to maintain the seagrass beds and keep them productive (much like mowing the lawn), and turtles recycle nutrients, making them available to many other animals and plants. Healthy seagrass beds ultimately mean healthy nurseries for invertebrates and fish, some of these are of commercial value and so important to human food security.
In Australia, green turtles are found from Shark Bay in Western Australia, around the northern Australian coast, throughout the Great Barrier Reef and as far south as Moreton Bay in southern Queensland. Some green turtles migrate within the western Pacific to places like New Caledonia, Papua New Guinea and Solomon Islands to feed.
The odds are stacked against green turtles. They regularly become entangled in discarded fishing gear and long-line nets, get struck by boats and die from ingesting marine plastics. Their nests are raided by feral animals, and those hatchlings that do emerge are frequently disoriented by lights, disturbed by people and vehicles as they struggle to make it safely to the water. Turtle hunting and egg collection by Indigenous communities continues and we’re yet to fully understand how turtles will be impacted by climate change. Because marine turtles have temperature-dependent sex determination, an increase in global temperatures could change the proportion of female and male hatchlings and bring instability to turtle populations. However, one of the biggest dangers lurking in our waters is sediment and chemical run-off from the mainland, coupled with insensitive coastal development.
New research supported by WWF is indicating that green turtles living near urban and farming areas are absorbing thousands of agricultural and industrial chemicals which may possibly be having a negative impact on their health. Other scientists are investigating the increased occurrence of the fibropapilloma virus (a herpes-like virus only found in the wild) in turtles and if run-off from land or marine pollution weakens the turtle's immune system, rendering it more susceptible to infection. In the period from 2010-2014, almost 6,000 turtles were found stranded – dead or dying – on the beaches of Queensland. Only a very small proportion of these turtles are rescued and rehabilitated, and eventually returned to the wild. In one single incident in June/July 2012, over 105 green turtles were founded dead and dying on the beaches of Upstart Bay, south of Townsville. This incident sparked the question – “Are coastal pollutants affecting green turtle health and the place they call home?”
- We don't yet know the full effect that run-off has on turtles, however it is worth remembering that the chemicals we flush down our toilets, apply to our gardens, spray on crops, or use in factories can end up in our river systems and ultimately the ocean.
- Turtle hatchlings use light and reflections from the moon to find their way to the water at night. Artificial lighting confuses them, so turn off lights visible from nesting beaches. Similarly, torches and people can disturb female turtles when they’re nesting. Give turtles – large and small – plenty of space as they emerge from or move toward the ocean.
- Never litter, and do your part to pick up any rubbish you see on the beach, in the park, or on the side of the road. Litter can be carried by the wind into our waterways and onto our beaches. Turtles can mistake garbage as food, especially plastic bags and balloons, which look like jellyfish.
- Don't buy products that have been made from sea turtle parts. Guitars, ashtrays, jewellery and other products made from sea turtles are sold to tourists around the world.