The Spanish-speaking man, who had a beard and long hair when he was discovered, said he had floated more than 8,000 miles from Mexico in a powerless 24-foot fibreglass boat.
He was spotted by two locals on Thursday when his boat floated onto a reef at Ebon Atoll in the Pacific.
Ola Fjeldstad, a Norwegian anthropology student doing research on Ebon, said: “His condition isn’t good, but he’s getting better.”
Ms Fjeldstad said the man, dressed only in a pair of ragged underpants, claims he left Mexico for El Salvador in September 2012 with a companion, who died at sea several months ago.
Details of his survival are sketchy, Ms Fjeldstad added, as the man only speaks Spanish, but has given his name as Jose Ivan.
She said: “The boat is really scratched up and looks like it has been in the water for a long time.
“He has a long beard and hair.”
Mr Ivan indicated to Ms Fjeldstad that he survived by eating turtles, birds and fish that he caught with his bare hands.
He also said that he drank turtle blood for hydration when there was no rain.
A turtle was found on the boat when it landed at Ebon.
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