3 days ago
Researchers map key north-south divide in Australia's orca population
A new study has mapped the key habitats for Australia's orcas and thrown fresh weight behind the theory there are two distinct species in the nation's waters.
Collating 1,310 sightings by whale watchers over four decades, researchers from Flinders University's Cetacean Ecology, Behaviour and Evolution Lab modelled orca species distributions and were able to pinpoint three key areas.
In the south, the Bremer sub-basin off Western Australia's southern coast and the Bonney Upwelling off south-west Victoria were pinpointed as key locations.
A population was identified in the warmer northern waters off Western Australia's Ningaloo Reef as well.
Lead researcher and PhD candidate, Melissa Hutchings, said each region highlighted the varying environmental preferences of Australia's orca population.
"Those off Ningaloo Reef, they're really drawn to those higher sea surface temperatures, strong productivity, and close-to-reef environments," Ms Hutchings said.
"Whereas, in the south-west and south-east, they're preferring lower sea surface temperatures, stronger currents and a lot of upwelling as well."
Ms Hutchings said their findings suggested there were two ecologically distinct types of killer whales in Australia.
They are temperate or tropical, based on their environmental preferences.
"As an apex predator, they will follow their prey aggregations, and then they will learn that is a predictable resource and will begin to specialise in that certain habitat," she said.
Ms Hutchings said further research was needed to ensure adequate protection for the whales.
"Commercial fishing, marine tourism, offshore drilling, chemical pollutants — all these things can have an impact, even on the ocean's top predator," she said.
On Ningaloo Reef, the orca season is off to a later-than-usual start, with some people speculating the delay could be a result of warmer-than-usual water temperatures.
The World Heritage site's winter feeding group was only spotted recently, hot on the trail of migrating humpback whales.
John Totterdell, a field biologist at Cetacean Research Centre (CETREC) WA, said it was the thrill of the hunt that most distinguished tropical orcas like those at Ningaloo.
"Killer whales in Ningaloo, for instance, have specialised in hunting humpback calves … they've got a strategy that's really precise," he said.
"The other thing they've got [is] their distinct dialect.
Dr Totterdell said skills like personality and familial roles were also handed down within the group, preparing younger whales for the challenges of life in the ocean.
"It's pretty tough to make a living if you're a killer whale in the tropics," he said.
"These humpbacks are only here for several months and some of the [orca] calves, in recent years, we have lost."
The temperate orcas are found further south in the Bremer Bay region.
"The orcas down in Bremer are offshore orcas living in a really deep water environment, so they're out over the continental shelf hunting anywhere between 700 and 2,000 metres," marine biologist Jennah Tucker said.
"They are known to hunt cooperatively, in particular in Bremer, it's the largest known aggregation of orcas in the southern hemisphere.
"In my time down there the most I've seen working together was between 70 and 80 orcas."
