Department of Wildlife and Fisheries spokesman Adam Einck said the five left the Venice marina in south Louisiana at about 6:30 a.m. Saturday but that their twin-engine boat's motor went out an hour later. The boat took on water and capsized.
Einck said three victims were from Alabama and one was from Louisiana. He said the survivor, a 33-year-old Alabama man, held onto a rope on the front of the capsized boat. The four became unresponsive, apparently from hypothermia. They were clinging to the side of the boat and four lifejackets, which they had not managed to put on as events unfolded.
The crew of an oil industry supply vessel found the survivor around 1 p.m. and transported him to a U.S. Coast Guard vessel. He was treated for mild hypothermia but refused hospital treatment.
The victims included the survivor's father and uncle and the uncle's girlfriend. Their names were being withheld pending notification of next of kin.
"They were not able to get out a distress call before this happened," Einck said.
Einck said the boat capsized about three miles offshore, near the South Pass entrance to the Mississippi River.
"It is believed that the four deceased succumbed to hypothermia," he said, adding that the survivor said they became unresponsive after about an hour. "The fifth was able to crawl on top of the boat that was capsized and we believe that was probably why he was able to get out of the cold water."
After the survivor was rescued, the bodies of the four victims were found floating in the water by the crew of the supply vessel and a Wildlife and Fisheries boat crew. The bodies were transported to the U.S. Coast Guard station in Venice.
The state Wildlife and Fisheries department is investigating the deaths. Officials were unable to recover the boat Saturday and will try again Sunday.