Scientists say they have recorded multiple sightings of elusive bigfin squid in Australian waters for the first time.
The researchers, led by the CSIRO, recorded the cephalopods in deep sea waters in the Great Australian Bight during two separate voyages.
Bigfin squid - or Magnapinna - are known for their long arms and tentacles and can measure up to seven metres in length. They are found kilometres beneath the ocean surface and there have only been about a dozen confirmed sightings of the animals worldwide.
The scientists took two voyages, the first in 2015, followed by a second in 2017. After processing hundreds of hours of camera footage, their findings have now been published in the journal Plos One.
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The scientists deployed cameras at depths of 946m-3258m. On the first voyage, they used a towed camera system which captured two sightings of the animals.
On the second journey, they used remotely operated vehicles which detected three more Bigfin squid.
Deborah Osterhage, who was one of the CSIRO scientists on both voyages, said the researchers were confident that each of the five sightings were separate individuals due to differences in their appearance, including their colour.
As well as marking the first time the animals have been recorded in Australian waters, it doubles the known records in the southern hemisphere.
Osterhage said the findings were significant because the animals are so rarely seen and much remains to be understood about them.
"They're quite a distinctive squid, so when you see them, you know you've really seen them and the fact they aren't seen very often is what makes them so appealing," she said. "They almost seem other-worldly."
Osterhage said in the past scientists had used a nearby object of a known size to estimate the size of Bigfin squid.
The research team were this time able to project lasers onto the body of one of the squid they recorded to determine a precise measurement, which came in at 1.8 metres.
"That was mostly made up of arms and tentacles. The body was only about 15cm," she said.
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Knowledge of deep sea cephalopods has been limited partly because specimens collected in the past were of animals that had been injured and killed by deep-sea fishing trawls.
In their paper, the scientists say underwater imagery had revolutionised study of the elusive fauna such as Bigfin squid because it enabled researchers to observe live animals in their habitat.
The two voyages covered a large area but the squid recorded were all sighted in locations that were close together. Osterhage said this was something the scientists would like to explore further.
"Normally when you find animals clustered close together it indicates something about their ecology," she said.
"It could be they have a specific habitat they like or it's related to reproduction. If we find they're in similar habitat that would give us clues as to why we're seeing this pattern."