Marine biologist hopes to figure out why sunfish strand along Australia's southern coast
Growing up to 3 metres long and weighing up to 2,000 kilograms, some species of sunfish are among the largest fish in Australian waters.
The smaller slender sunfish draws attention for a different reason, with the fish washing ashore on beaches on Australia's southern coast every year.
When Marianne Nyegaard first saw a sunfish, it drastically altered the trajectory of her life and started her down a path to solving the mystery of the strandings.
The encounter took place while scuba diving in Bali in 2012.
"I realised that people knew nothing of these fish up there and it's a massive tourism industry around this seasonal phenomenon of sunfishes coming into the reefs up there," Dr Nyegaard said.
"I flew home and quit my job and started a PhD on these fish."
The primary focus of her research at Murdoch University in Perth was to discern the impact of tourism on the fish.
But it was not long before a new element was unexpectedly added to her research.
"Through doing population genetics, I found another species of sunfish that wasn't described," she said.
"We called it the hoodwinker sunfish because it had been hiding in plain sight.
"There's been a tonne of interest in sunfishes going back to the 1500s and lots of species had been described that later turned out to be all the same one.
"In all of this mess of names and descriptions, this fish just slipped through the net and was never discovered.
"It was a huge honour to be able to name this tricky fish hiding in plain sight."
During this time, Dr Nyegaard became aware of what appeared to be the habitual stranding of a much smaller member of the sunfish family on WA shores.
"It's sad to see them die and it's also very sad to see tonnes of them on the beaches," she said.
"But I do believe it is a natural phenomenon."
The sometimes "brutal" mass stranding of the slender sunfish became the focus of her citizen science project.
For more than a decade, Dr Nyegaard has been building a dataset of strandings around Australia, almost all of which occur in WA between Albany and Cheynes Beach to the east.
"Some years there are hardly any, and other years there are hundreds or even thousands of fish that strand," she said.
"My biggest year was in 2016 … one day we counted just about 1,000 sunfish stranded on the beaches in Albany.
This dataset enabled Dr Nyegaard to confirm previous studies ruling out post-spawning mortalities as the cause of the strandings.
Nor do pollution or toxic algal blooms appear to be associated with the events.
The next hypothesis to investigate was whether the strength of the Leeuwin Current had anything to do with the scale of the strandings.
"By collecting data over a long time, we hope to be able to figure out if the strengths of these stranding years are correlated with certain oceanographic features," Dr Nyegaard said.
"I'm also hoping in the next year or two to have my data curated and ready for analysis."
The citizen science project, however, will not end there.
"I am kind of suspecting there might be some longer-term patterns here that we need decades of data to be able to see, so that's why I'm hoping to just keep it going."
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