A lone pilot whale calf has been euthanised at Eagle Bay after mass stranding at Toby Inlet near Busselton

Vets have euthanised an orphaned pilot whale calf spotted swimming close to shore at Eagle Bay on Friday amid concerns it could send out distress signals that could lead to another mass stranding in the South West.

Nearly 30 long-finned pilot whales died at Toby Inlet near Busselton on Thursday after about 160 beached themselves.

Authorities and volunteers managed to assist more than 100 of the pilot whales to head back out to sea.

On Friday, a disorientated 1.5m juvenile pilot whale was seen circling moorings near Eagle Bay boat ramp.

Department of Biodiversity, Conservation and Attractions senior marine operations officer John Edwards said it seemed likely the animal’s parent had perished in Thursday’s stranding incident.

After monitoring it for several hours in the hope its distress calls would bring a parent, wildlife officers pulled the calf aboard a boat and took it inshore for tests.

Without its mother and unable to feed by itself, he said its long-term prognosis was poor and the only option was euthanasia.

“The animal certainly wasn’t moving the way we’d expect to see whales move,” Mr Edwards said. “We noticed it was listing to one side, its respirations weren’t normal.”

Perth Zoo veterinary manager Rebecca Vaughan-Higgins said there was no humane alternative for the whale calf.

“From a veterinary and welfare perspective, that was the best outcome for that individual,” she said. “It certainly wouldn’t have survived in the wild.”

Earlier, DBCA wildlife officer Pia Courtis said there was also a possibility the juvenile could attract other pilot whales close to shore where they could beach themselves again.

“It is a concern, and that’s why we have the spotter plane and vessels out in the ocean to see what’s going on,” she said.

Mr Edwards said the DBCA would also continue to monitor a pod of whales located offshore from Eagle Bay and other pods dispersed through the Capes area.

“Without seeing any animals today ... we’re hopeful that they’re back doing their thing, well offshore,” he said.

Quindalup Beach had been closed while one dead pilot whale that had washed up there overnight was removed.

Whale documentary maker Steve Tribbeck — who works with the not-for-profit group Geographe Marine Research — said he arrived at Eagle Bay about 7am on Friday following reports a lone calf had been spotted in the water close to shore.

“One of our members of Geographe Marine Research was flying his drone over the top of the calf, just monitoring the calf and ... there were two members of the public that were with the calf,” he said.

“They were waist deep in the water and I did see that this calf was really quite feisty, it had a lot of energy. There was a lot of splashing in the water and they’d turned the animal and were pushing it out to sea.”

Geographe Marine Research chair Ian Weise said earlier on Friday the calf was likely “getting quite hungry” because it was dependent on its mother for food.

“It’s vocalising and making noises and could attract a pod — if there’s one out there — close into shore, and we could see a repeat of what happened yesterday,” he said.

Mr Weise said there were various theories about why whales beached themselves, including that the shape of Geographe Bay could interfere with their sonar or that the pod followed one sick whale into shore.