Thousands of dead shearwaters have washed up on beaches on Australia's east coast, and researchers are unsure of the cause and scale of these seabird “distresses.”
The 20-metre-long shearwater, also known as the Yura or Muttonbird, flies 15,000 km from the Northern Hemisphere to southern Australia and back each spring. Dead shearwaters have been spotted on the coast of south-east Queensland since late October, with similar reports appearing in New South Wales and Victoria in recent weeks.
Dr Lauren Roman, who studies petrels at the University of Tasmania's Marine and Antarctic Research Institute, said it was “difficult” to understand how many birds had died and whether it was a normal event or a mass die-off.
These deaths are often referred to as seabird disasters, she says.
Shearwater shipwrecks are known to occur during annual migrations, but smartphones and social media have increased people's awareness, she said.
“There is a perception that mortality rates are increasing, but it is very difficult to determine whether this is actually the case or whether it is simply due to increased awareness.
“If they were hundreds of kilometers offshore, in the middle of the Tasman Sea, and there was a mass fatality, we wouldn't see it.”
Even if only a small portion of the population dies near the coast, dozens or even hundreds of people could wash ashore.
“It's very difficult to quantify whether the number of deaths is actually higher than in the past,” she said.
Jennifer Lavers, a researcher at Adrift Labs, said that based on early analysis by citizen scientists, the number of adult birds “washed up dead on beaches” this year is in the “hundreds or thousands.” estimated. report.
The mass mortality event is unusual for long-lived seabirds and “doesn't make sense from an evolutionary perspective,” she said.
Lavers said the stranded birds were weakened and indicated they were struggling to find enough food.
Roman said there was a significant mass mortality event in 2013 in which millions of seabirds died. Recent reports have not been on the same scale.
The 2013 phenomenon was thought to be related to an unusual thermal phenomenon in the North Pacific known as the “blob.”
“We know it caused a series of seabird die-offs in the Northern Hemisphere as well, and the early stages of that coincided with the period when petrels were there before they started migrating,” Roman said.
Dr. Eric Woehler, who has studied seabirds for more than 40 years, said shearwater disasters often occur in the fall when chicks head north for the first time, and occasionally in the spring when the adults return. He said the timing, duration and number of birds involved in the fatalities varied from year to year.
“These birds in particular don't have enough food, and we think they basically started migrating with insufficient body reserves,” he said.
Shearwaters live to be over 40 years old, so the loss of adults likely had a major impact on the entire population due to loss of reproductive effort, Wahler said. Each pair of seabirds laid only one egg and raised one chick each year.
Tasmania and the Bass Strait Islands were home to this species.
Authorities were also wary of the highly pathogenic and highly contagious H5N1 influenza strain, which had not yet been detected in shearwaters found in Australia or on local beaches.
Roman said researchers are working hard to determine the causes and effects of the sinking.
She says while these events can be heartbreaking to witness, people don't need to be alarmed just yet. “If you find one or two dead bodies, don't worry too much, it's normal at this time of year.”
Beachgoers should avoid touching dead birds or allowing pets to interact with birds.
People can contact wildlife guardians if they see live birds that appear to be in distress, and can also report more dead seabirds to the state's marine animal stranding hotline. .
