"It's hard for me to imagine someone surviving 13 months at sea," said Ambassador Tom Armbruster in Majuro. "But it's also hard to imagine how someone might arrive on Ebon out of the blue. Certainly this guy has had an ordeal, and has been at sea for some time."
Other officials were reacting cautiously to the Spanish-speaking man's story while they try to piece together more information.
If true, the man's ordeal would rank among the greatest tales ever of survival at sea.
Mexico's Foreign Relations Department says the man told Mexico's ambassador to the Philippines, Julio Camarena, that he set out from an area near the coastal town of Tonala in southern Chiapas state, which would mean his journey covered a distance of more than 6,500 miles (10,460 kilometers), if he drifted in a straight line.
Armbruster said the soft-spoken man complained of joint pain Monday and had a limp but was able to walk. He had long hair and a beard, the ambassador said, and rather than appearing emaciated he looked puffy in places, including around his ankles. Otherwise, he added, Alvarenga seemed in reasonable health.
Armbruster, who speaks Spanish, said the survivor told the following story:
He's a native of El Salvador but had lived in Mexico for 15 years and fishes for a man he knows as Willie, catching sharks for 25 pesos ($1.90) per pound.
On Dec. 21, 2012, Alvarenga left Mexico in his 23-foot (7-meter) fiberglass boat for a day's fishing, accompanied by a teen he knew only as Ezekiel, who was between 15 and 18.
A storm blew the fishermen off course, and soon they were lost and adrift.
"He talked about scooping up little fish that swam alongside the boat and eating them raw," Armbruster said. "He also said he ate birds, and drank birds' blood."
After about a month, Ezekiel died, the survivor told officials.
Alvarenga also talked about eating turtles. Once near Ebon, he swam ashore.
"He thanked God, initially, that he had survived," the ambassador said. "He's very anxious to get back in touch with his employer, and also with the family of Ezekiel. That's his driving motivation at the moment."
In Costa Azul, a fishing hamlet near Tonala, fishing boat owner Villermino Rodriguez Solis, who assumes his son is the "Willie" that Alvarenga referred to, said Alvarenga and a companion had gone missing on Nov. 18, 2012, which would imply the sea odyssey lasted 14½ months.
"Here, his colleagues went out in boats to look for them. They spent four days looking for them," said Villermino, who expressed surprise that Alvarenga had been found alive in the Marshall Islands.
Residents of Costa Azul said they didn't know Alvarenga's real name. He had shown up looking for work years before, but worked from fishing camps along the coast. They knew him only by a nickname, "La Chancha," used to describe heavy-set people. It was clear he was an experienced fisherman, they said.