Captain Aurelio Agac-ac is free after a military push into a terrorist stronghold in Basilan in the southern Philippines.
Agacac and chief engineer Laurencio Tiro were abducted by terrorists, believed to belong to the Abu Sayyaf group, last Thursday.
Some local reports indicate that Agac-ac escaped while his captors slept. Others indicate that the abductors abandoned Agac-ac to delay pursuing troops and evade a firefight.
Agac-ac and Tiro were believed to be on the M/V Super Shuttle Roro 9 at the time of their kidnapping. They were two of 11 crewmen from a tug M/T Tug R9 that was towing the ro-ro from Cebu to General Santos.
The Philippine military has mounted an offensive against the Abu Sayyaf in Sulu and Basilan. The group is believed to be holding nearly 30 hostages, mostly seafarers.
Philippine President Rodrigo Duterte has threatened to impose martial law in the south, home to the majority of Filipino Muslims, to address security problems there.