The men, a 50-year-old Port Kennedy man and a 57-year-old Cooloongup man, departed Coral Bay in an 8.2m vessel and should have returned before sunset.
Their boat trailer and car were still parked at the boat ramp at Monk Head on Monday.
A land, sea and air search, involving a plane, police boat, Volunteer Marine Rescue boats and quad bikes, failed to locate the men at the time of going to print.
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READ NOWNumerous items, believed to have come from the vessel belonging to two missing fishermen, were found on Monday.
On Wednesday, divers of a charter vessel found a human arm on the sea floor near Bill’s Bay. Police attended and divers retrieved the arm. It will undergo forensic examination.