Colonel Aggrey Quarshie did not reveal when the vessel was seized, but said a ship named as Mariam was located thanks to a tracking device the Nigerian gunmen did not find, Reuters reported.
"The Ghana Navy responded swiftly with a patrol team to the area and they were able to overpower the pirates and free the ship. But when they got there, the cargo had already been transferred to another vessel," Quarshie said.
The crew was unharmed, he added.
A search has been launched for the vessel believed to have stolen the tanker’s cargo: 1,500 tonnes of crude destined for Lome in Togo.
All Africa Media cited Makase Sunday, executive director of Nigerian-flagged Mariam's owner Maxweir Nigeria, as saying the company was told by the gunmen that they had hijacked the vessel, and that they were going to sell the cargo and use the proceeds and the tanker to hijack other ships.
As soon as that message was delivered, the entire communication system in the vessel went down.
Sunday said that when the ship arrived off the coast of Cotonou, Benin, it veered off track.
The owner suspected that it was heading towards Ghanaian waters, so he informed the navy there.
On Saturday, the pirates realised Ghana's navy was trailing them, took cover among the crew and concealed their weapons.
The eight suspects were named as Molih Williams, 32; Peggy Aki, 32; Ebiyaibo Amos, 32; Molih Klisman, 31; David Jacob, 30; Ayetimiyi Oyinle; 29, Pinamo Saniyo, 26; and Picolo John, 25.
They were found with four AK47 assault rifles, 300 rounds of live ammunition loaded in magazines, one pump action gun, three VHF radios, 18 mobile phones, one digital camera, seven wrist watches and cash.
