Manus Provincial Police Commander Chief Inspector David Yapu issued the warning following the arrest of youths who stole from MV Manus.
Owned by Papindo Trading, the ship captain and his wife were held up, assaulted and had items worth K4,779 stolen on Sunday.
The vessel was anchored near Rara Island when the suspects, who are known to police, held it up.
One arrest has been made, with more expected to follow.
Meanwhile, another youth from Pateku Island, in the Nigoherm LLG in Western Manus, was killed after he was struck with a spear last week Thursday.
The suspect is known to police and the community.
PPC Yapu said a sharp metal object penetrated the deceased’s shoulder and reached his lungs, causing his death.
The deceased was 27-year-old Kosko Lukas. His body could not be brought to Lorengau for postmortem due to the current strong North-West winds.
However, PPC Yapu said his CID officers will travel to the island to further investigate and establish the cause of his death once the weather improves.
(Boats at Lorengau boat shed)