https://www.abc.net.au/news/2023-01-30/ ... /101897876
Hundreds of orcas are now congregating at the Bremer Canyon off Western Australia's south coast to search for food and find a mate, but scientists still don't know where they come from.
The apex predators make the journey every year between January and April to hunt for deep-diving whales and fish species like tuna and giant squid.
According to a researcher observing the orcas, the pods spotted this season off Bremer Bay were matriarchal and led by a grandmother who had knowledge of hunting.
However, the knowledge of the existence of the orcas in the area is relatively new, with scientists only becoming aware of their migration through the "hotspot" just over a decade ago.
It's still not known where they come from or where they go.
Research into clever killers
Marine biologist Jennah Tucker conducts observational research on the orcas so that they can be better understood.
Ms Tucker said the black and white sea creatures, also known as killer whales, were so intelligent they had even worked out how to remove satellite tags.
"There have been quite a few attempts at tagging orca, but they've been quite unsuccessful. They're really, really clever animals," she said.
"They're basically, sort of like: 'Oh, what's that on your back? Let me get that off, and then there goes a $10,000 tag."
She said her team gets photo ID of the animals by getting shots of their dorsal fins and eye patches — which are equivalent to the fingerprints of humans.
"We're just trying to piece together the different family structures and the different pods that we see regularly," she said.
This year the animals were led by a grandmother who had knowledge of hunting.
The sea creatures get in formation and hunt silently in a line to cover more ground.
The pods usually include anywhere between five and 15 whales.
When they find food, there is sometimes an oil slick that can be seen from the surface or a distinct smell.
Another sure sign the whales have hit the jackpot is the presence of seabirds trying to feed on the leftovers.
Orcas vs sharks
Ms Tucker said there were places around the world where orcas predate on sharks.
"If I were a shark, I wouldn't be hanging too closely around an orca that is feeding," she said.
"We don't tend to see them [sharks] in amongst all of the action."
Bianca Uyen, a marine biologist onboard Naturaliste Charters, said it was suspected that great white sharks left the area when orcas arrived.
She said there had been reports of great white shark populations in South Africa fleeing when orcas came through.
It took the great whites a long time to return, according to the African Journal of Marine Science, which published a research paper on the topic in 2021.
Need for protection
Kane Watson, Naturaliste Charters whale spotter, said orcas spent 80 per cent of their time hunting.
He said the whales sometimes got curious about the boat when their bellies were full.
"We have to stick about 50m away from them, and these guys [the whales] don't know the rules and come right up to us," he said.
Mr Watson said the tours helped fund research about the whales so that they could be better understood.
He also called for people to take care of the ocean.
"Make sure you're cleaning up after yourself to keep our oceans healthy," he said.
Ms Uyen also said it was important to ensure tourism was sustainable.
"A focus must be on minimising our impact on the environment and giving back to research," she said.
"We can reduce our impact by educating passengers of whale and dolphin research and conservation, following the Australian National guidelines for whale watching and removing the use of plastic onboard."
- An orca breaches in the Bremer Sub-Basin off the coast of Western Australia.(Supplied: Naturaliste Charters)
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