Citizen scientists from around the world have pored over nearly 14,000 images to help determine threats faced by fur seal colonies in Victoria.
The SealSpotter Challenge is run by Phillip Island Nature Parks, and volunteers who take part count seals in photographs of colonies at Seal Rocks off Phillip Island, and The Skerries near Mallacoota.
Marine scientist Rebecca McIntosh said volunteers spent 500 hours on this year's challenge, which was more than last year.
"We had 124 participants this challenge [compared to] 187 the year before but I think that was because more people around the world were in lockdown," Dr McIntosh said.
"Last year we had 9,280 images counted and this year 13,789. That's a lot of images – so we're really excited that fewer people got more done.
People from 15 different countries took part, including Australia, the US, Spain, United Kingdom, Italy, Netherlands, Norway and Portugal.
Understanding seal deaths
Participants analysed drone images taken at Seal Rocks when pups were being born and then another set of images taken a month later.
"What we're seeing is basically every year the number of pups that are born is pretty stable but the number of pups that survived to the end of December or the start of January, can be quite variable and usually a lot lower than the number that are born," Dr McIntosh said.
"So we're seeing high mortality in pups after birth."
This year there was a decline of more than 1,000 pups from 3,562 down to 2,248.
"One of the things we think it could be attributed to is high PFAS levels in the pups, and PFAS is a flame-retardant chemical," she said.
"We think that they're getting it through the diet, their food supply, and then they store it in the fat and the mums can pass it across the placenta."
She said she thought pups were ingesting "a dump" of the chemicals through their milk after being born, which could be affecting their survival rates.
"We've got a PhD also at the University of Melbourne … looking at abortive disease agents so diseases that are in a population that might cause early births, and that might cause mortality soon after birth as well," she said.
The data is also being used to look into the population impacts of entanglements with marine debris, including recreational fishing line.
"We're not actually sure whether the amount of entanglements and mortality to entanglement is causing population level effects," she said.
