There have been two high profile shark encounters in Tasmanian waters in less than a fortnight — what is happening?
On Wednesday, a father and son videoed the moment a shark collided with their boat as they were observing a seal colony at Tenth Island, around 10 kilometres off the coast of Beechford in the state’s north.
It happened less than two weeks after a 10-year-old boy was pulled from a boat into the water by a shark of Tasmania’s north-west coast on July 17, with the child’s father jumping in to save him credited with saving his life.
Experts have said while these types of encounters are infrequent, they are also not surprising.
Professor Culum Brown from Macquarie University has been working in the field of shark behaviour for over 10 years, and said it was uncommon for sharks to come near boats.
“It’s pretty unusual for them to approach boats unless the people are fishing or something like that, and then they’re chasing a hooked fish into the boat,” he said.
“Occasionally when it does happen, and it is rare, it’s more often that it’s a kayak, a kayaker or a stand-up [paddle] border or something like that, where the silhouette actually looks a bit like a seal from underneath.”
Searching for food — and a cooler climate
Professor Brown said seals are also likely responsible for the close encounters with sharks in Tasmanian waters recently.
“Their [sharks] behaviour is driven by food and whatever moves their food around, that’s what moves the sharks around, and that can be ocean currents and upwellings and those sorts of things.”
He said unusually warmer waters along Australia’s east coast also play a role in bringing seals, and consequently sharks, further south.
“The East Coast Current is actually pushing further down into Tasmania than it would normally … and that’s only going to continue to strengthen as we move forward with climate change,” he said.
“One thing that you can guarantee is that where there are seals and seal colonies, and particularly seal pups, then there will be white sharks,” Professor Brown said.
Given that, Professor Brown said being anywhere near a seal colony would be “more than enough” to encounter a shark.
“If you were driving your boat or going fishing anywhere around the seal colony, then you’ll probably encounter sharks in one way, shape, or form.”
Adaptable, but vulnerable
Shark researcher and author Chris Black said white sharks are part of the Lamnidae family, meaning they are able to adapt to cooler waters — like those in a Tasmanian winter — making them a common predator at this time of year.
“They [Lamnidae] are all ectothermic, that means that they can keep their body temperature above that of the surrounding seawater,” he said.
“Some people call it almost like a warm-blooded shark, even though that’s not technically correct, but they are able to regulate their temperature in that way.”
Mr Black said it is difficult to estimate how many sharks would currently be lurking in Tasmanian waters as they don’t tend to stay in the one area.
“It’s almost impossible to say in fact, white sharks are so cosmopolitan. They’re cruising over the ocean the whole time.”
But Professor Brown said there are fewer sharks than people might expect across the entire east coast of Australia
“[Our east coast population] estimates are around about 800 adult individuals only, and if you include juveniles, it might be up around the 2,500 mark is the best ‘guesstimate’,” he said.
“There are not a lot of animals on the east coast of Australia at all, and in fact, white sharks are federally listed for conservation protection for that very reason.”
Caution, and understanding, vital out at sea
Both shark researchers said boaters and fishers should be careful on the water knowing the presence of seals will generally mean there’s also sharks nearby.
“We just have to keep in mind, sharks are doing their thing. They’re in their environment, and we actually represent a far greater threat to sharks than the other way around,” he added.
Mr Black agrees, saying people on the water need to ensure they exercise caution, but understand they’re in the shark’s territory.
“It’s very hard to keep an eye out for a shark, but it is something to keep in mind,” he said.
“We must understand whether we go out in boats or whether we go diving or surfing, we shouldn’t stop doing those things.