Three of the four people whose ship capsized off the coast of southwest Nova Scotia early Saturday morning have been released from hospital, says the son of the ship's captain.

The crew of the Poseidon Princess called for help in the early morning hours, saying their boat was in danger of capsizing off the coast of West Pubnico.

Morgan d'Entremont says his father Martin and the other two crew members, Lee and Oscar d'Entremont, who are Martin's brothers, were injured.

"They're a little banged up," Morgan d'Entremont said.

The three crew members were able to get in a life raft, but the fourth person, a Fisheries Department observer who was taking samples on the Poseidon Princess, was not able to climb aboard.

"They kept yelling for him and after a few waves, they got separated from him pretty quickly," said d'Entremont.​

The Joint Rescue Co-ordination Centre put out a call for boats in the area to help around 1 a.m. AT.

Two fishing boats responded to the call and found three people in a life raft and a fourth in the water, all of them wearing survival suits, according to Reetha d'Entremont, the wife of the ship's captain.

The rescue effort was supported by a Cormorant helicopter and a Hercules plane from 413 Transport and Rescue Squadron, the primary air search and rescue unit on Canada's East Coast.

The Cormorant lowered a search and rescue technician to provide medical support as required, according to the Twitter account of Joint Task Force Atlantic.

By 5 a.m. all four men were rescued.

Reetha said the three crew members were all taken to a Shelburne hospital for treatment. The Fisheries Department observer was taken by ambulance to a hospital in Yarmouth, she said.

According to Morgan d'Entremont, he is doing fine.

d'Entremont says the crew is unsure why the vessel sunk.

"They said the weather was actually relatively decent," he said, adding the swells were not very high.

The vessel had 115,000 pounds — or about 52,000 kilograms — of haddock on board, said d'Entremont.

The Poseidon Princess is operated by Inshore Fisheries Limited, a fish processing and harvesting company in Pubnico.