Police say a man who disappeared in Foveaux Strait left a note in his belongings.
Nicholas Duncan, 44, of Nelson was last seen on a ferry about 6pm on Tuesday, halfway between Bluff and Halfmoon Bay on Stewart Island.
Air and ocean searches since then have not located Mr Duncan, and police say the chances he has survived in the cold water are slim.
An aerial search Wednesday was concentrating on the shorelines of Stewart Island and the northern Muttonbird Islands.
Police say inquiries are continuing with the man's family, but do not believe anyone else is connected with his disappearance.