It's an astonishing tale, and, if true, would represent one of the greatest survival-at-sea stories of all time. But is the story told by Mexican fisherman Jose Salvador Alvarenga true?
Alvarenga says he and a young helper left the Mexican state of Chiapas to fish in September or December — the story varies — 2012, about 14 months ago. Several days ago his small, battered boat washed up on a reef in the Marshall Islands with Alvarenga looking worse for wear, but not in such bad shape considering the ordeal.
He claims to have survived on turtles, a few birds, fish, sharks, rainwater and his own urine, and maybe he did. But experts contacted by NBC News have their doubts.
"If everything lined up perfectly, I suppose it could happen," said Jonathan Wright, an expert on sailing and water safety. "But it's a longshot," added Wright, who is Vanderstar Chair at the United States Naval Academy but was not speaking for the academy.
The current record for survival at sea appears to be Poon Lim, a sailor whose ship was sunk about 750 miles off the coast of Brazil by a German submarine during World War II. According to Ruthanne Lum McCunn, whose book, "Sole Survivor: The True Account of 133 Days Adrift" tells Lim's tale, he lived off rainwater collected in a large piece of canvas, fish he caught with makeshift hooks and rope, and a bird.
At one point, McCunn told NBC News, Lim did briefly drink his own urine during a long period without rain.
But 133 days is a lot shorter than roughly 400. And Lim had some advantages. For example, the raft came equipped with a storage tank for water. Alvarenga's boat apparently did not, and unlike Lim, drinking urine seems to have been a major part of his survival strategy.
While drinking urine may help extend life very briefly, the U.S. Army Field Manual says "DO NOT drink urine, fish juices, blood, sea water." This is because your kidneys have already concentrated wastes into urine. Putting that concentrate back into your body will only force the kidneys to concentrate waste products again and again. You'll die.
As for drinking turtle blood to survive thirst, Richard Rosenblatt, professor emeritus of ichthyology at San Diego's Scripps Institution of Oceanography said, "there'd have to be an awful lot of blood in that turtle."
Rosenblatt, a veteran of many long research sea voyages, is also skeptical of Alvarenga's explanation for what he ate.
"I can't see him catching sea turtles," Rosenblatt told NBCNews.com. "There aren't that many of them running around far out to sea and though they do cross oceans on migration, they mostly live in coastal waters."
As the sailors who took part in Thor Heyerdahl's famous 1947 voyage aboard Kon-Tiki discovered, fish can be hard to find in the deep oceans, too.
"I don't know how he would catch sharks," Rosenblatt said. "Most species are coastal, except the pelagic whitetip. You do see them and I have been on ships where we've been stationary and threw out a chunk of bait and a hook and we've caught them, but you need a hook and a good sized steel leader or their teeth would cut it."
Of course, one possibility left unsaid by reports concerns the young man who left Mexico with Alvarenga. Partway through the ordeal, Alvarenga has said, the young man died and was buried at sea. But Alvarenga wouldn't be the first person trapped in an extreme survival situation to turn to cannibalism.
The fisherman's survival for roughly 14 months adrift "isn't plausible," Rosenblatt said. "But of course, just because it's not plausible doesn't mean it didn't happen."
Wright believes the only way to really know is by a close examination of growths on the boat's hull. If the growths match a 14-month journey, then maybe it really was a miracle.