There was no reasonable hope the missing men from the No 1 Insung were still alive after 30 hours in the icy Southern Ocean without proper immersion suits, Maritime New Zealand said.
“Survival times for crew members in the water would be very short,” rescue coordinator Dave Wilson said.
“The medical advice is that those who did not suffer cardiac arrest on entering the water would likely be unconscious after one hour and unable to be resuscitated after two hours.”
Three South Korean trawlers searched overnight but found no crewmen in the remote area 1,000 nautical miles north of the McMurdo Antarctic base and 1,500 nautical miles from New Zealand’s southern tip.
“Unfortunately, the Southern Ocean is an extremely unforgiving environment… sadly, it is exceedingly unlikely that anyone not picked up yesterday could have survived,” Mr Wilson said.
The trawler sank suddenly at 6:30am Monday (local time), with its owners saying it may have collided with an iceberg.
Maritime NZ said the vessel went down so fast it did not send an SOS and crew members had no chance to don protective gear as they scrambled to escape.
Another South Korean trawler, the No 707 Hongjin, plucked 20 fishermen from the ocean shortly after the boat sank. Maritime NZ said none required medical treatment.
A coastguard spokesman in the South Korean port of Busan, where the ship was based, said there were eight Koreans, eight Chinese, 11 Indonesians, 11 Vietnamese, three Filipinos and one Russian on board.
The nationalities of the dead are not known.
The freezing conditions and remote location meant the prospect of finding anyone alive was always slim.
It would have taken days for ships from New Zealand to steam to the area and Maritime NZ said sending a plane was also “not viable” because it was an eight-hour flight.
In addition, Maritime NZ said it was not told about the accident until Monday afternoon, more than six hours after it occurred.
The stricken trawler was fishing for patagonian toothfish, a rare species that lives in waters so cold Greenpeace says it has a form of anti-freeze in its blood.
The fish, marketed as Chilean sea bass, is popular in South America, the US and Japan and is often illegally caught.
Greenpeace, which says the patagonian toothfish is known as “white gold” in the industry for its highly valued flesh, lists it as a species in danger of being unsustainable.