ABC Science /
By environment reporter Nick Kilvert
4/19/2021
The short-nosed sea snake used to be abundant on Ashmore Reef
(Supplied: Schmidt Ocean Institute/Conor Ashleigh)
A species of extremely rare, endemic sea snake not seen on Western Australia's Ashmore Reef in 23 years has been rediscovered living in the "twilight zone".
A species of extremely rare, endemic sea snake not seen on Western Australia's Ashmore Reef in 23 years has been rediscovered living in the "twilight zone".
Key points:
17 species of sea snake disappeared from the shallow reef in the '90s and 2000s
This is the 3rd species to have been rediscovered living at depth
Genetic tests are needed to determine if it's a unique species
The critically endangered short-nosed sea snake (Aipysurus apraefrontalis) is known from a couple of sites on the north coast of Western Australia, and was once abundant in the shallows of Ashmore Reef before it seemingly disappeared in 1998.
But scientists on board a research vessel equipped with "advanced robotic technologies" found the snake in 67 metres of water last week, according to sea snake researcher Blanche D'Anastasi from the Australian Institute of Marine Science (AIMS).
"The robot was looking at a dead shell and [the researchers] were trying to pick it up and it had a sea snake sitting next to it," Ms D'Anastasi said.
"They asked to zoom in on it and they [both] realised straight away it was a short-nosed sea snake.
"They contacted me soon after and were like, 'is this what we think it is?'"
Ashmore Reef sits about 320 kilometres off Australia's north-west coast.
(Supplied: Geoscience Australia)
Ashmore Reef, which sits about 320 kilometres off the north-west coast of Australia, was once home to one of the most abundant assemblages of sea snakes on the planet, but began mysteriously disappearing.
"They've been gradually declining since the '70s, but things started really going awry in 2002," Ms D'Anastasi said.
"You used to find about 50 snakes per day if you were walking the reef site.
"By 2002 it was down to 20 snakes per day, by 2010 it was down to 10, and then in 2012 there were no snakes left in the shallows."
By 2012, 17 species had vanished from the reef, according to Ms D'Anastasi.
The short-nosed sea snake is now the third of those 17 "disappeared" sea snakes to have been rediscovered by scientists on board the Schmidt Ocean Institute's Research Vessel Falkor.
The find offers a chance for recovery and protection of the species, according to Nerida Wilson from the Western Australian Museum, who was on board the vessel when they made the find.
"This discovery shows that we have so much more to learn about the twilight zone, and we are hopeful to find more of Ashmore's lost sea snake species," Dr Wilson said in a statement.
The twilight zone, also called the mesophotic zone, refers to ocean depths between about 30m and 150m where some sunlight still penetrates.
Discovery could be a separate species
Ashmore Reef, which sits about 320 kilometres off the north-west coast of Australia, was once home to one of the most abundant assemblages of sea snakes on the planet, but began mysteriously disappearing.
"They've been gradually declining since the '70s, but things started really going awry in 2002," Ms D'Anastasi said.
"You used to find about 50 snakes per day if you were walking the reef site.
"By 2002 it was down to 20 snakes per day, by 2010 it was down to 10, and then in 2012 there were no snakes left in the shallows."
By 2012, 17 species had vanished from the reef, according to Ms D'Anastasi.
The short-nosed sea snake is now the third of those 17 "disappeared" sea snakes to have been rediscovered by scientists on board the Schmidt Ocean Institute's Research Vessel Falkor.
The find offers a chance for recovery and protection of the species, according to Nerida Wilson from the Western Australian Museum, who was on board the vessel when they made the find.
"This discovery shows that we have so much more to learn about the twilight zone, and we are hopeful to find more of Ashmore's lost sea snake species," Dr Wilson said in a statement.
The twilight zone, also called the mesophotic zone, refers to ocean depths between about 30m and 150m where some sunlight still penetrates.
Discovery could be a separate species
The researchers spotted the snake curled up near a dead shell.
(Supplied: Schmidt Ocean Institute/Conor Ashleigh)
The short-nosed sea snake is a venomous species that grows to just over a metre in length. It is usually a brownish-purple colour with light banding across its body.
It's in the Elapidae family — a group of snakes characterised by their short, hollow, fixed fangs — which includes land species like the taipan, death adder and cobra.
The rediscovery of the snakes living at depth on Ashmore Reef has thrown up more questions than answers, according to reptile ecologist Kate Sanders from the University of Adelaide.
The species was presumed extinct after it disappeared from Ashmore, but were found living in a few isolated coastal habitats by Dr Sanders' team in 2016.
"Cable Beach in Broome, we've had a single specimen from there, and scattered distributions from the Exmouth Gulf," she said.
The short-nosed sea snake is a venomous species that grows to just over a metre in length. It is usually a brownish-purple colour with light banding across its body.
It's in the Elapidae family — a group of snakes characterised by their short, hollow, fixed fangs — which includes land species like the taipan, death adder and cobra.
The rediscovery of the snakes living at depth on Ashmore Reef has thrown up more questions than answers, according to reptile ecologist Kate Sanders from the University of Adelaide.
The species was presumed extinct after it disappeared from Ashmore, but were found living in a few isolated coastal habitats by Dr Sanders' team in 2016.
"Cable Beach in Broome, we've had a single specimen from there, and scattered distributions from the Exmouth Gulf," she said.
The sea snake hadn't been seen on the Ashmore Reef in 23 year.
(Supplied: Schmidt Ocean Institute/Conor Ashleigh)s
But the coastal specimens are morphologically different to the Ashmore snakes, with a smaller head that appears suited to foraging for eels in shallow sandy and seagrass habitats, Dr Sanders said.
Genetic testing could reveal them to be separate species.
"The coastal and the Ashmore populations have these genetic and morphological and ecological differences," Dr Sanders said.
"So, depending on what you consider a species to be, they could easily be considered a separate species."
But the coastal specimens are morphologically different to the Ashmore snakes, with a smaller head that appears suited to foraging for eels in shallow sandy and seagrass habitats, Dr Sanders said.
Genetic testing could reveal them to be separate species.
"The coastal and the Ashmore populations have these genetic and morphological and ecological differences," Dr Sanders said.
"So, depending on what you consider a species to be, they could easily be considered a separate species."
What is unclear from the photos of this new snake spotted at Ashmore Reef is whether it's a coastal specimen that has migrated out to the reef recently, or if it shows that the Ashmore population has persisted this whole time at depth.
The solution will be to catch and take genetic samples from a specimen at Ashmore, and compare it to a coastal specimen.
If it turns out to be a coastal specimen, this will provide useful information in itself.
Part of the reason the short-nosed sea snake was presumed extinct when it disappeared from Ashmore Reef was because it was thought to have an extremely limited range — as little as a few kilometres.
"Could they have re-colonised from the coast? That's a really important question,"
Dr Sanders said.
"If it's the coastal population that's recolonised, that would suggest we've lost that historical diversity that used to be present on Ashmore."
"If it's the coastal population that's recolonised, that would suggest we've lost that historical diversity that used to be present on Ashmore."
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