Teams will now focus their search on a wider area.
The alarm was raised about 6pm yesterday when an overdue boat in the Catlins area did not return.
Last night a marine search and rescue operation was launched, running out of Owaka and involving rescuers from south Otago and Dunedin.
Fog hampered the search efforts overnight but a large-scale search was launched again this morning.
The missing pair are both from Owaka and were on a fishing trip in their silver 5.2 metre pontoon-style Kiwicraft boat, called Krystella.
Police say they left Catlins Heads about 8.30am yesterday and were expected back before dark.
Searchers are continuing to look in areas north and south of where Mr Kopua's boat was found overturned.
There have been coastal searches of beaches, aerial searches with helicopters and an aeroplane, plus boats have been on the water all day looking for the missing persons.
The search will continue through the day and again tomorrow.