Sharks acting out of stress, not aggression, during SA’s toxic algae bloom, experts say
Experts have weighed in on whether it’s safe to swim in our waters after several videos emerged of sharks acting erratically as algae suffocated their habitat. See the video.
Sharks behaving strangely during South Australia’s toxic algal bloom are acting out of stress, not aggression, experts say, but beachgoers are still being warned not to take risks if they encounter one near shore.
Several videos have emerged this year showing sharks and rays swimming erratically along the coastline, with some even beaching themselves.
Watch episode three of the exclusive new algal bloom mini series in the video player above
- Watch episode one of Save our Summer: The Bloom’s Grip
- Watch episode two of Save our Summer: The Ripple Effect
Prominent marine ecologist and shark researcher Professor Charlie Huveneers from Flinders University said anyone who spots a shark “exhibiting weird behaviour” should be cautious, particularly around larger species.
“In the case of potentially dangerous species, like white sharks or large bronze whalers, unless you really know what you’re doing, I would recommend that people not risk it by dragging sharks out,” he said.
He said the unusual behaviour being seen, including sharks lingering close to shore or beaching themselves, was likely linked to the harmful algal bloom.
“I got a lot of reports of people trying to take that shark and put it back out at sea, but a shark five minutes later, coming back on the beach as well,” he said.
“This is not usual behaviour for sharks, obviously and it’s likely linked to these brevetoxin or some of the other toxins that can be produced by the species of algae found in these bloom.”
However, he stressed there was no evidence the bloom was triggering more attacks.
“There’s no indication the algal bloom is leading to more shark bites,” he said.
“What we’ve seen hasn’t been aggressive behaviour. It’s been stress behaviour, when the sharks are trying to survive rather than trying to hunt and consume prey.”
Marine conservationist Dr Mike Bossley had a close brush with that stress driven behaviour in May when he was snorkelling with friend Pam Bennett at Treasure Cove on the Yorke Peninsula.
Pam was seriously injured after being struck by a stingray in what experts described as an unprovoked attack.
Rescuer Dave Hentschke said the 68-year-old narrowly avoided death after a 16cm stingray barb pierced her arm about 50m offshore.
“We had quite a few species starting to wash up, and one day Pam and Mike went out for a snorkel to have a look,” he said.
“She swam over a group of stingrays and one of them, sick and stressed from the algae, came up behind her and flicked its barb into her arm.”
Mr Hentschke said the barb missed a major artery by just millimetres.
“If that would have done the same thing to Steve (Irwin). She would have definitely been in a lot of trouble.”
Professor Huveneers said the current situation was a reminder that people should always be alert when entering the ocean, bloom or not.
“I think that regardless of the algal bloom, with more people being in the water and with shark population recovering, there’s going to be a lot, it’s likely to be an increased risk of shark bites,” he said.
Professor Huveneers said the algal bloom has triggered mass deaths among sharks and rays, but warned the biggest threat is to species found nowhere else.
The coastal stingray and pygmy thornback skate, which exist in very low numbers across small parts of South Australia, face “a real likelihood of impacting the entire species”, potentially driving populations down and putting them “at risk of extinction”.
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Originally published as Sharks acting out of stress, not aggression, during SA’s toxic algae bloom, experts say
