Jose Salvador Albarengo, 37, a fisherman from El Salvador, told officials that he survived more than a year adrift in the Pacific Ocean, drinking turtle blood and catching fish with his bare hands.
Albarengo said he went on what was supposed to be a one-day fishing trip more than a year ago from Mexico, but was blown out to sea.
He was found in a disoriented state on a remote coral atoll, Reuters reported.
But the acting secretary of foreign affairs for the Marshall Islands, Gee Bing, said he was skeptical of Albarengo's account.
"It does sound like an incredible story and I'm not sure if I believe his story," Bing said. '"When we saw him, he was not really thin compared to other survivors in the past. I may have some doubts. Once we start communicating with where he's from, we'll be able to find out more information."
Albarengo was found with no identification with him.