A boat captain has been killed after being speared by a swordfish in Hawaii.

Randy Llanes had been trying to catch the 18kg, 1.8metre fish with a spear gun, according to the Hawaii Police Department.

The 47-year-old experienced seaman was in the water at Honokohau Harbor on the west coast of the Big Island when he spotted the broadbill swordfish.

When the animal was hit with a hunting weapon, it began to thrash about – prompting the fisherman to jump into the water alongside it. However, amid the struggle, it fatally punctured Mr Llanes’s chest.

Another reported suggested that "the fish got wrapped around a mooring anchor, came back and swam at him".

Emergency crews attempted CPR, but the man later died in hospital from the puncture wound.

"Randy has been fishing all his life," his friend explained to local media. "He's a pretty accomplished fisherman. He actually caught a 500lb [226kg] marlin yesterday." 

Hawaii supplies much of the rest of the US with swordfish catch. The fish is fast-moving and predatory, often using its long, distinctive bills to attack prey.

Andrew Rossiter, director of the Waikiki Aquarium, told Hawaiian news agency KHON that the carnivore may have been pursuing a school of smaller fish into shallow water or was injured.

Heidi Dewar, a fisheries research biologist with NOAA Fisheries in California, told the National Geographic that reports of swordfish injuring or killing people are incredibly rare. "Normally, you wouldn't see a swordfish swimming around in the harbour," she explained.

"These are open-ocean animals that are more often found over deep water."

Mr Llanes is survived by his wife and two small children.