Raffaella Ciccarella, in 9NewsCom, 10 August 2022, where the tile runs thus “Australia’s own snake island, where ‘giant’ tiger snakes slither” …. with highlighting added by The Editor Thuppahi
Mount Chappell Island is part of the Furneaux Group, within the Bass Strait, and is managed by the Aboriginal Land Council of Tasmania.
It is uninhabited and located off the island state’s north-east corner.
The rocky outcrop skirted by azure blue ocean is said to support a “dense population” of venomous black tiger snakes, which reach lengths of over two metres.
Only a select few have set foot on the isolated shores, Queensland man Shane Black is one of the lucky few. He was granted permission to visit and touched down on Chappell Island April 2018, spurred on by his lifelong fascination with venomous snakes.
“I’ve always wanted to go to Chappell Island since I was very young after I learnt about the giant tigers that lived there,” he told 9news.com.au. “A few years back I decided to make it happen.
“I seen around 40 in a day. The biggest I seen were around 1.6 metres, which is large by tiger snake standards.”
While large, Black said the island tiger snakes have a “fairly relaxed” demeanour. “(But) they will bite if harassed,” he added. “I’m actually hoping to get back there in the next year or two.”
Chappell Island tiger snakes are considered the largest of all the tiger snakes, and according to University of Melbourne’s School of Biomedical Science, may reach lengths of 2.4 metres. They survive on an annual six week feast of mutton bird chicks – a protein-rich migratory bird that only lands in Tasmania – before they are forced into a period of fasting.
Evolutionary biologist with the University of Canberra Dr Vicki Thomson said there’s a chance the reptiles are the oldest snakes to evolve in isolation within Australia.
“They’ve probably been isolated there since the Last Glacial Maximum when sea levels rose and cut them off,” she told 9news.com.au. “They’ve got a long history on that piece of land”.
Thomson said she’s not surprised by the fact the snakes on Chappell Island seem to be reaching such extreme lengths.
She explained two factors could be contributing to this.
“Snakes are perpetually growing,” she said.”And on these islands there’s often not many predators for the snakes, so they can keep growing and growing. There’s nothing really there that can predate on them apart from the other snakes, so the gigantism may actually just be the fact they are really old. (But) there’s another island phenomenon, where you can see both gigantism and dwarfism depending on the animal you’re looking at.”
Chappell Island tiger snakes also happen to be the most prolific venom producer of all the black tiger snakes, with an average venom yield of 74mg.
To compare, mainland snakes have an average venom yield of 35mg.
“Venom volume isn’t necessarily what makes a bite deadly, but rather the level of toxicity,” Australia Reptile Park Reptiles Keeper Sam Herrmann told 9news.com.au. “Toxicity and volume are very species-dependent, however some larger species such as king brown snakes do typically produce a larger venom yield.”
The toxicity of Chappell Island tiger snakes is said to be less than that of mainland tiger snakes, but antivenom should be sought immediately after a bite.
While the Chappell Island tiger snake has developed a fearsome reputation, Thomson said they’re not the only snakes that have found themselves cut-off from the mainland. She said “there’s lots of islands in South Australia where tiger snakes live because they’ve been cut off by sea levels”, and pointed to Carnac Island in Western Australia, where tiger snakes were also introduced by humans.
What scientists don’t know is why tiger snakes seem to be the species most prone to island isolation – and adaptation. “That’s the million dollar question,” Thomson said.