To save a turtle, Caitlin Smith, a graduate student at the University of the Sunshine Coast, half swam, half crawled through mud on a tube. She tied a harness around his chest and flippers so the rest of the team could carefully pull him to safety. It was just one of 15 diseased green turtles our team spotted in the Great Sandy Strait near Queensland’s Hervey Bay in recent weeks.
Turtles aren’t the only ones struggling at the moment. A dead dugong was found nearby, while another emaciated dugong was found alive up the Noosa River.
you are starving. Huge rainfall and flooding have washed large amounts of sediment out to sea, where it smothers the seaweed these sea creatures rely on. There is no relief in sight as we enter our third wet year of La Niña.
Why is this happening?
Most of the sick sea turtles we found — as well as those found by the Queensland Department of Environment and Science team — showed signs of starvation and disease, including the newly identified softshell turtle disease.
What is behind these deaths is the rains and flooding that La Nina has brought.
Like much of New South Wales and Queensland, the Great Sandy Strait has been badly hit by flooding this year, with three major floods inundating the Mary River. Flooding has carried massive amounts of sediment into Hervey Bay, reducing water quality and washing pollutants into the habitat of sea turtles and manatees.
In normal years, sediments from rivers bring a flood of nutrients that can actually trigger a seagrass boom as water quality improves. The problem is, there was just too much sediment. With one La Niña after another, seagrass has had a harder time recovering or regrowing.
Read more: Seagrass restoration can bring coastal bays back to life
As the sediments from the floods spread across the shallow seas, the water became cloudier. Soon the sunlight could no longer penetrate the gloom to reach the seagrass beds. Worse, floods release a cocktail of chemicals, including pesticides and herbicides, that are unintentionally washed down farms and flooded communities.
The result was widespread devastation in the Great Sandy Straits region. In May this year, a team from James Cook University surveyed 2,300 square kilometers in the region and found almost no seagrass left in waters between 1 and 17 meters.
Green sea turtles and dugongs are the grazers of the Australian seas and rely heavily on seagrass. In good years they will drift across these lush seagrass meadows, which resemble grass fields on land, and feed as they go.
In the summer, our seagrass beds usually flower, allowing turtles and manatees to fatten up for the winter. In winter, seagrass dies off naturally. This year, local sea turtles and dugongs went into winter in poor condition after failing to fatten up during the summer season.
That’s why we see so many sick or dying animals. From January 1 to August 31 this year, Turtles in Trouble Rescue volunteers transported 91 local sea turtles to the nearest wildlife hospital, 300 kilometers away. In contrast, in 2019, before the start of the La Niña cycle, the group had only 12 transports.
Is there no food anywhere else?
In flood-affected areas, turtles and dugongs have only two choices: move away or try to eat something else.
During the great floods of 2010, Hervey Bay dugongs were found more than 200 kilometers south in Moreton Bay off the coast of Brisbane. Unfortunately, their migration didn’t fare much better – the seagrass in Moreton Bay had been hit by sediment from the Brisbane River. But we do know that some survived.
Others were found dead, washed up 900 kilometers south, after trying to find food and failing. Turtles can also migrate, but they are often so debilitated by starvation diseases and parasites that they die before they can find an alternative food source.
What about finding something else to eat? When our team analyzed the stomachs of dead sea turtles from the Hervey Bay area, we found that many were full of mangrove leaves.
Unfortunately, these trees contain a number of natural toxins designed to deter animals from eating them, such as the toxic sap of the milky mangrove. Worse, as the “kidneys of the coast,” mangroves use their leaves to store concentrated salt and toxins like heavy metals. In short, this diet is not a substitute.
Is this part of a natural boom and bust cycle?
While turtles and dugongs exhibit natural variations in their populations over time – and often due to food availability – there are limits. Turtles and dugongs cannot respond to climate-related pressures the way fast-breeding mice can.
Female green sea turtles must be 30 to 40 years old before they can reproduce. Only every three to eight years do they undertake their long migrations to reproduce. They lay over 1,000 eggs in hopes that just one hatchling will survive the dangerous seas long enough to reach reproductive age.
Dugongs, on the other hand, only raise a single calf every three to seven years. These reproductive strategies make it very difficult to respond to rapid changes in their environment.
Consecutive lean years caused by consecutive La Niña events will affect both the survival rate and reproductive ability of these animals.
Sea turtles in poor condition cannot migrate successfully, meaning they are headed for a poor nesting season. Dugongs will fight too. Without fat reserves, the females cannot support their calves until they are weaned. That will make it harder to replenish population and recover from losses from starvation or resettlement. We will not know the full impact of this event for years to come.
In response to the crisis, local volunteers have stepped up. The Turtles in Trouble Rescue group has grown from five to 50 trained members and is working with the University of the Sunshine Coast to establish a sea turtle rehabilitation center in the area. We are better prepared for the next flood event.
Read more: Dugongs: A glimpse into the gentle sea creature’s past can guard its future