As hopes for Andrew Gray and the others faded, five passengers who managed to reach the shore told of their six-hour swim.
Mr Gray, from Headington, escaped the wreckage of the Twin-Otter aircraft after itcrashed on Saturday during a one-hour flight south from Espiritu Santu, an island in the Vanuatu archipelago about 625 miles west of Fiji, to Port-Vila on the island of Efate, the capital of Vanuatu.
He was slightly injured in the crash and became detached from the rest of the group as they swam towards the shore five miles away. Four Vanuatu nationals and two French nationals, including the pilot, were all still missing last night.
"The Englishman that was with us had some mild injuries from the crash and he began to drift off and we never saw him again," said Neil Watts, a Seventh Day Adventist, one of those who swam to safety.
Mr Gray went to the South Pacific two weeks ago to work for IWGIA, an organisation involved with indigenous people throughout the world. He had been due to travel to Papua New Guinea in the next few days.
Mr Gray, who had written several books about his work among the Arakmbut tribe in the Amazon basin of Peru, had been working with the United Nations on developing a permanent forum to discuss the rights of indigenous tribes.
Last night, his wife, Sheila, was being comforted by Mr Gray's older brother, Richard.
"She is very distressed and trying to cope with a very difficult situation," he said. "We are not very optimistic now at all. It has been such a long time."
The couple's 17-year-old son, Robbie, was at school as usual yesterday. The five who escaped the crash were recovering in Port-Vila.
Mr Watts and two other Australians, a Swede and a man from Vanuatu, said yesterdaythat they prayed as they tried to stay together in rough seas off Port-Vila. Mr Watts said: "I called out to people, `If any of you have a faith in a God, I would like to pray with you'. So we actually had prayer in the water."
Mr Watts said the aircraft was being buffeted by a storm when it suddenly lost altitude and hit the sea. "Water rushed in through the cockpit. It was filling fast, we had just a few seconds to get out. There were several who never came out."
Mr Watts said his group of six had only two life-jackets between them. They began swimming towards the distant lights of Port-Vila while another group of three or four disappeared into the darkness.
"For several hours we were heading towards lights but we weren't going anywhere because of strong currents. I wasn't too hopeful. I was suffering badly from the cold, I was suffering cramps. I was starting to wonder whether I would make it," he said.
Two of the survivors were Flight Lieutenant Tim Hurford, from Australia, and his wife, Nicola Leeks. Flight Lieutenant Hurford said: "Conditions were awful. Every 15 or 20 minutes the monsoonal rain came through. The rain was blinding."
However, they were saved when the tide turned and the group was carried towards a beach. They reached a beach house, where the owner made them coffee and called the police.
Chris Poll, from the British embassy at Port-Vila, described the survivors as "very lucky".