CASTRIES, St Lucia (REUTERS) - Authorities on the Caribbean island of St. Lucia said they have arrested five people in the murder of a British tourist who was travelling around the world with his wife.

The victim, Roger Pratt, 62, was on a trip with his wife, Margaret, ahead of her 60th birthday when their boat, Magnetic Attraction, was boarded by unidentified attackers on Friday, police said. Mrs Margaret Pratt was also treated for injuries.

Three people were arrested over the weekend, and police announced two more arrests on Tuesday. A post mortem examination indicated that Pratt drowned after suffering a traumatic blow, according to police.

Mrs Margaret Pratt found her husband floating in the water. He was pronounced dead at a hospital. The BBC reported that the couple lived in Moreton Paddox, near Stratford-On-Avon in Warwickshire.

The murder has raised concerns on the small, eastern Caribbean island, where tourism accounts for about two-thirds of the economy.

"I wish to assure you that as a destination St. Lucia remains relatively safe for nationals and visitors alike," said Ms Lorne Theophilus, the tourism minister. "We are fully committed to seeing this investigation through to a final conclusion."