"I can hear the pirates talking and the big ships calling each other so they are very near," Capt Pacheco said, speaking to BBC security correspondent Frank Gardner by satellite phone.
"Who knows what is in the offing. They might plan an attack during the dark and capture us in the absence of protection."
A German warship visited the tanker yesterday to give the crew of 23 emergency food, water and medical aid, according to a spokesman for an EU naval force patrolling the area.
But it has since had to move on to another task, leaving the Stolt Strength and its 23 crew with no protection.
The EU says that if it receives a distress call it will respond.
However, Capt Pacheco said that would be of little help when it could take pirates just five minutes to scale the ship and get on board.
"If they attack us again there's no chance to call protection," he said.
"We need round-the-clock protection."
He also said the crew had been denied food during their captivity, receiving only scraps.
"We [were] malnourished, weak and [had] low morale during our ordeal," said.
The Stolt Strength was seized in November 2008 while it was carrying a cargo of phosphoric acid from Senegal to India.
The owner of the vessel, Sagana Shipping Inc, declined to say whether any ransom was paid for Tuesday morning's release.
International warships have been patrolling the waters off Somalia and in the Gulf of Aden in recent months as part of an effort to counter piracy.
They have freed a number of ships, but attacks have continued.
When first loaded, the map's focus falls on Somalia where most of the pirates are based. Use the arrow icons to scroll left towards Europe and the United States which are both playing a central role in tackling the problem.
Scroll to the right for a story about the Philippines, which supplies many of the world's mariners.
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