Up to 160 whales were found on the shore at Toby Inlet near Dunsborough, more than 250km south of Perth, on Thursday.
Community members helped save more than 100 but the Department of Biodiversity, Conservation and Attractions reported 28 long-finned pilot whales died.
The department on Friday said a juvenile pilot whale had been found about 14km away at Eagle Bay beach and the Parks and Wildlife Service would monitor it.
"There is also a pod of whales located offshore from Eagle Bay and other pods dispersed throughout the Capes area," a spokesman said.
Authorities have closed nearby Quindalup Beach as staff work to remove a whale carcass that washed up earlier in the day.
The mass stranding on Thursday involved four pods of whales spread along 500m of beach, with a further two pods spotted offshore.
Most of the whales appeared to be adult females with a few calves, a marine expert said.
About two hundred volunteers helped to turn the whales so they could breathe and splashed water on their backs while they were beached.
The last mass stranding of whales in WA was at Cheynes Beach in Albany in July 2023 where at least 90 of the mammals died.
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