In April, Sunil signed a four-month contract with UK-based shipping company Union Maritime and took charge of the vessel MT Ocean.
He is also registered with Mumbai-based crew management firm Accord Marine Management.
In July, his family said, the vessel was attacked by pirates off the west coast of Africa.
However, when Sunil decided to stop in Togo on July 31 and report the incident to the authorities, the ship's crew were themselves arrested.
While all other crew members were subsequently released, Sunil, the ship's master and third engineer remain imprisoned.
