Sharks could linger off Perth coast despite whale carcass removal

Some of Perth's most seasoned swimmers are taking a break from the ocean after a whale carcass lured sharks close to shore, with an expert warning that the predators could be attracted to the area for weeks.

Several sharks have been spotted lurking off some of Perth's most popular beaches in recent days after a whale carcass washed up at City Beach on Monday, just over a week after a fatal shark attack at Sorrento Beach.

The City of Perth Surf Life Saving Club cancelled the Surf Life Saving WA (SLSWA) Enduro Championship at City Beach today, while placing all club-based training on hold until further notice.

City Beach, Floreat Beach and Swanbourne Beach have all been closed.

But the heightened shark activity in recent days has also discouraged swimmers and surfers further along the coastline.

Cottesloe's community ocean swimming group PodSquad is taking a break from its daily 2-kilometre morning swim.

"Even though the [Cottesloe] beaches are open at the moment, we're taking a break for a few more days," the group's founder Shane McGurk said.

"Our numbers will drop off now, understandably — it's a very emotive issue. [Some] people have a different relationship with these sort of events, about how they manage.

"Some want to get straight back in [and get] back on the horse, so to speak, and others want to take a break and come to terms with the tragedy at Sorrento, and also the whale at City Beach."

Calls for more tagging, AI drones

Ahead of each summer, around the end of October, the Town of Cottesloe installs a shark barrier at Cottesloe Beach.

But this year, it is due to be installed a couple of weeks early — on Wednesday, depending on weather conditions and seaweed movement.

Mr McGurk said PodSquad members would initially swim within the enclosure when members returned to their morning routine, and they would like to see the enclosure installed early again next year.

The group also called for an expansion of the shark tagging program and for investment in AI-powered drones that are capable of identifying shark species when the animals come in close to shore.

He said that could enhance the data available to swimmers when they were making decisions about whether to get into the water.

"We just want to know where the sharks are, and when we know where the sharks are we can keep safe," he said.

Sharks could linger for weeks

Curt Jenner from the Centre for Whale Research in Western Australia said while the whale carcass had been removed from City Beach, sharks could still be attracted to the area for weeks.

"Whales are full of blubber and that blubber will break down into oil very quickly and that gets straight into the sand," he said.

"Sharks are cued in, on a molecular level, to detect small traces of oils or blood or anything like that and so they'll be tasting that for weeks to come."

Mr Jenner said sharks were also attracted to the south-west coastline between September and December because that time was the peak of the southern migration for humpback whales.

The predators also follow other prey, such as blue fin tuna, into the southern ocean.

"If you were going to be cautious about being in the water, this is the time," Mr Jenner said.