Article by Ella Humphreys

When I first swam alongside a green sea turtle around Lady Elliot Island, I was struck by the slow and easy way it pulled itself through the water with its front flippers. It moved above a coral and seagrass meadow teeming with fish of all sizes and colours; some fish moved as an aggregate shoal while others drifted with the sway of the current. 

Recently, I went snorkelling offshore from Minjerribah (also known as North Stradbroke Island), one of three sand islands that hem Moreton Bay. When I encountered sea turtles again, I started to think about the challenges they face. The sea turtle is one species that has been so clearly affected by anthropogenic change: environmental change or pollution originating in human activity. 

Moreton Bay, which lies 14 kilometres from the centre of Brisbane city, provides habitat and feeding sites for an incredible array of marine animals and migrating shorebirds. Except for Kemp’s ridley sea turtle, Moreton Bay is home to six of the world’s seven sea turtles. It is home to herding dugong, dolphins, sharks, rays, and hundreds of fish species and is visited by seasonal migrating humpback whales and southern right whales. It seems impossible to talk about one species without referring to a myriad of other species; we live alongside and/or in dependence upon so many other animal and plant species. Sea turtles are an important part of the marine ecosystem, helping to recycle nutrients, balance food webs, and maintain healthy seagrass beds and coral reefs.

Moreton Bay, a relatively sheltered and shallow marine environment, receives the outflow of five rivers (the Albert, Logan, Brisbane, Pine and Caboolture). These rivers receive plastics and chemical pollutants from the activities of a city of more than 2 and a half million people, including their commercial, agricultural, and industrial activities. The 2022 flood carried heavy sediment loads into the Bay, affecting seagrass beds, an important source of food for turtles and dugongs. Flooding events highlight the importance of revegetation projects along creeks and riverbanks to prevent erosion. 

Sea turtles are reptiles whose evolutionary lineage stretches back to the time of the dinosaurs: the leatherback turtle is considered to be much the same as it was 110 million years ago. They have remarkable navigation abilities. While it is not exactly certain how it is done, turtles can navigate by detecting variations in the Earth’s magnetic field. Turtles can detect a combination of the strength of the magnetic field and the angle that the magnetic field lines make with the surface of the earth. They use these components, much like latitude and longitude, as a kind of “magnetic map,” which helps them navigate between feeding and nesting grounds. There is strong evidence that turtles imprint the geomagnetic signature of their birthplace, and this information is retained until they need to return to their birthplace to nest. 

Turtle Survival

Increased beach activity during the holiday season means there are more recreational boats out on the water, and therefore, a greater risk turtles will get hit. As turtles and dugongs are surface-breathing animals, they often get hit by speeding boats as they come up for air. Boat strikes are a leading cause of death or injury for turtles. Like road speed restrictions, turtle and dugong go-slow speed limits are in place to prevent harm. 

Around 1 in 1000 turtle hatchlings survive to adulthood. The age at which turtles can reproduce varies across turtle species and populations. Because green turtles eat mostly seagrass and seaweed as adults, they reach sexual maturity at a later age, between 20 and 50 years of age. Turtle nesting and hatching in Queensland occurs between November and April. 

The holiday season coincides with turtle nesting, creating risks for the survival of hatchlings. The use of off-road vehicles on the beach poses the risk that nests may be crushed or sand compacted over nests. To avoid making wheel ruts that can hinder the hatchling’s progress to sea, it is advised that vehicles should be kept to the hard sand well below the high tide mark.

At night, artificial light can prevent mothers from coming ashore to lay their eggs. Bright lights also affect hatchlings’ ability to see reflected celestial light across the sea horizon when they emerge from the sand. If artificial light is too bright, they can become disoriented and head towards land instead of out to sea. 

Sea turtles are currently nesting in the dunes on one of Moreton Bay’s sand islands, Yarun (Bribie Island). Citizen scientists and volunteers from the TurtleCare Sunshine Coast program and the Bribie Island Turtle Trackers monitor nesting mothers and relocate or fence nests if eggs are laid below the high water mark or in the near-dune traffic zone. Their dedication and effort increase the chance of turtles surviving. 

In north Queensland, the Cairns Turtle Rehabilitation Centre, a volunteer organisation, cares for sick and injured turtles brought in from the Great Barrier Reef and the Cape York Peninsula. The turtles cared for suffer from disease and/or injuries caused by boat strikes, discarded fishing gear, or ingested plastic that is mistaken for food. 

Lost or abandoned fishing gear—nets, lines, ropes, or traps, known as “ghost nets” is a global problem. Since the growth of the mass production of plastics from the 1950s onward, the world’s oceans have accumulated lightweight, relatively inexpensive synthetic nets that float in the ocean potentially for decades, if not centuries. The impact of ghost nets and plastics cannot be understated—up to 14,600 turtles were caught in 8,690 ghost nets across northern Australia in 7 years. 

Millions of tons of discarded plastics enter the world’s waterways each year. Marine animals like turtles and birds swallow them or become entangled, causing injury and death. Since 2022, the sale of lightweight plastic bags has been banned in supermarkets in all states and territories across Australia due to the devastating impact they have had on the marine environment. Jurisdictions across Australia have committed to banning certain single-use plastics. I am convinced legislation across jurisdictions, on a global scale, must be enacted to phase out the majority of mass-produced consumer plastics for the sake of all beings. The word of the next 50 years should be biodegradable!

Climate change is driving air and sea temperatures higher, impacting the sex of sea turtles. Unlike human beings, the sex of turtles isn’t determined at fertilisation by XY chromosomes. The temperature of the sand during incubation determines whether the turtle develops as male or female. While pivotal temperatures vary across populations, on average, if the nest temperature is above 31 degrees centigrade, all turtles will be female; below 27.7 degrees, they will all be males. With increased temperatures, greater numbers of female turtles are being born in the northern Great Barrier Reef, while males are still hatching in the cooler southern Great Barrier Reef. A trial study conducted in Cape York has shown that shade cloth can protect nests from rising temperatures, providing a difference of 6.58 degrees compared to sites with no shade.

Kemp’s ridley turtle

In an incredible collaborative conservation effort, the Mexican and U.S. governments and the Gladys Porter Zoo worked together for decades to save the Kemp’s ridley turtle from extinction. A secondary nesting site was established at the Padre Island National Seashore in South Texas. 

In the 1970s, the bycatch of turtles in shrimp trawling posed an imminent threat to turtles’ survival. The U.S. National Marine Fisheries Service, with the help of the commercial shrimping industry, invented a device called the turtle excluder device (TED), which ensures turtles don’t get drowned as bycatch in shrimp nets. It is now mandatory that shrimp trawlers operating in the U.S. waters of the Gulf of Mexico and the South Atlantic use it. It has dramatically reduced turtle deaths. 

While there are challenges, many people are working together for the survival of sea turtles and marine animals. It is truly inspiring.  

“Hope is often misunderstood. People tend to think that it is simply passive wishful thinking: I hope something will happen but I’m not going to do anything about it. This is indeed the opposite of real hope, which requires action and engagement.”

– Jane Goodall, The Book of Hope: A Survival Guide for Trying Times