What on Earth Are We Doing to Our Sea Turtles?

Dr Jane Barker

What on earth are we doing?

Over millions of years our oceans have evolved into a complex sustainable ecosystem, each organism from the plankton to the ocean giants playing their unique role. When any species becomes threatened by extinction, we are forced to investigate the reasons behind this and to look at the part humanity is playing. The impact of humans on our turtle population is sadly readily apparent in those brought into the Australian Seabird and Turtle Rescue centre in Ballina - from pollution to fishing, habitat destruction and climate change these gentle creatures who have inhabited our oceans for aeons are being harmed and put at risk of extinction.

By developing a greater understanding of turtles and their vulnerability to human impact we can practice not only effective conservation biology but learn to love these magnificent creatures who grace our shores.

Plastics

“Fishing entanglements and plastic ingestion also continue to be major problems for marine turtles.” - Jen Slape, Assistant General Manager, Australian Seabird and Turtle Rescue

Annually it has been estimated that 8-12 million tons of plastic from both coastal and inland areas reach the world’s oceans. Once in the marine environment, plastics may persist for hundreds of years. Exposed to sunlight and wave action plastics gradually fragment into micro and nano particles. In these forms they are readily ingested by all sea creatures, reaching humans along the food chain. In the sea most of the plastic stays close to the shoreline. Microplastics get caught up in sea grass and kelp forests.

Hatchlings seek refuge and sustenance within floating sargassum seaweed mats. Hatchlings with stomachs full of plastics they can’t expel may die of malnutrition. Plastics not only pollute the ocean surface but once fragmented reach the ocean floor.

Floating plastic debris travel thousands of miles on the ocean currents, trapped eventually in massive whirlpool-like islands of garbage. Plastic refuse now reaches even the world’s most isolated and pristine coastlines. Turtles have been found to have ingested plastics which entered the ocean far from their foraging grounds.

Turtles may mistake plastic bags for jelly fish. This can cause bowel obstruction, a sense of fullness leading to starvation or trap air causing floating syndrome when the turtle is unable to stay underwater in their foraging grounds. The Australian Seabird and Turtle Rescue centre has rows of glass jars containing plastics retrieved from turtle’s stomachs.

“We see a steady stream of patients affected by both.” - Jen Slape, Assistant General Manager, Australian Seabird and Turtle Rescue

From plastics and fishing gear to habitat destruction and rising temperatures, the greatest threat to sea turtles is no longer nature - it is us.

Fishing equipment

“There has been a rise in hook and line ingestion and entanglements in both marine turtles and seabirds and shorebirds.” - Jen Slape, Assistant General Manager, Australian Seabird and Turtle Rescue

Both recreational and commercial fishing are a danger to turtle populations. In the past turtle were hunted for their shells, decimating populations. In Australia all turtles have been protected since 1968. Turtle deaths are caused by injury by boats, getting caught in nets preventing them from returning to the surface to breathe, or injuring their fins, ingestion of fishing gear nets, fishing line or rope and by habitat destruction through use of dragnets.

Bottom trawling leads to severe ecological damage to the seagrass beds turtles forage on. This causes not only destruction of the seagrass but damage to the seabed from which recovery is slow. Fisheries regulation include the use of turtle expulsion devices (TEDs) fitted to the front of trawling nets and bycatch reduction devices which allow sea snakes and under size fish to escape. Governments are also regulating use of dragnets in eco sensitive areas and close to shore. Australian turtles often forage in areas of the Pacific where it has not always been possible to effectively police any of these fishing practices.

Habitat destruction

“The impact of humans on our turtle population is sadly readily apparent in the animals brought into our centre.” - Jen Slape, Assistant General Manager, Australian Seabird and Turtle Rescue

The destruction of Australian sea turtle habitat is occurring both on nesting beaches and across offshore foraging grounds, threatening the long-term survival of the species common to the NSW North coast region: Green, Loggerhead and Hawksbill Turtles. While coastal development and light pollution disrupt nesting and hatchling orientation, serious impacts are occurring at sea, where turtles spend most of their lives. Migration to areas in the Pacific where it is more difficult to police habitat protection make our turtles even more vulnerable.

Different turtle species have different foraging habits. Adult Green Turtles are purely vegetarian, depending largely on sea grass meadows which can be damaged by pollution from agricultural runoff and industrial activity, and weather events such as cyclones and heatwaves. Hawksbill Turtles depend on reef associated sponges which are impacted by coral bleaching due to rising sea temperatures. Loss of feeding grounds leads to malnutrition which in turn leads to loss of immunity, with infections and impact on reproduction.

Turtles are long lived and according to species do not reach reproductive maturity until they are between 10 and 40 years old. Hatchlings and young turtles are very vulnerable to natural predators so loss of habitat can have a profound effect on the survival of the species.

Climate change

“Currently, the most prominent human impact on our marine turtles is climate change and how habitats and foraging grounds are affected by severe weather systems.” - Jen Slape, Assistant General Manager, Australian Seabird and Turtle Rescue

Many turtles nest on remote Pacific beaches which may be affected by climate change related sea rise. Coral reefs and sea grass meadows are impacted by rises in the sea temperature affecting the turtle’s diet, leading to malnutrition and disease. The sex of hatchling turtles can be affected by the temperature of the sand, the hotter it is the more female hatchlings. Studies in the Northern Great Barrier Reef in Queensland indicate that temperatures above 29.1°C produce mostly females, nearly 99% of juvenile, subadult and adult Green Turtles are female - questioning the sustainability of the species as temperatures rise.

Turtles have survived on earth largely unchanged from the time dinosaurs roamed the land. Human impact has the potential to be devastating, leading if uncurbed to extinction. The plight of the sea turtle is mirrored in other sea creatures and unless humanity takes responsibility, changing what can be changed, the whole marine ecosystem is threatened. By developing a greater understanding of turtles and their vulnerability to human impact we can practice not only effective conservation biology but learn to love these magnificent creatures who grace our shores.

Get involved or donate to Australian Seabird and Turtle Rescue.