At least this one has an explanation. From the Australian Broadcasting Company:
Dozens of oceanic sunfish have been found dead on Goode Beach and at Frenchman’s Bay.
The sunfish is native to tropical and temperate waters.
The department’s senior research scientist Dr Kim Smith says a strong current is dragging large numbers of sunfish to cooler, southern waters.
“This time of year is associated with the Leeuwin Current flowing across the South Coast at its strongest,” she said.
“It’s that warm water current and it brings these fish down, this year we have a really strong Leeuwin current and there’s a lot washing up.”
Dr Smith says hundreds of sunfish washed up on the South Coast in 2008 due to the current.
“It’s possible that this event might be a bigger one, in terms of more fish washing up than the 2008 event,” she said.