This is the sixth shark attack in Hawaii this year, according to the Hawaii Division of Aquatic Resources.
On Saturday, a man was killed in an apparent shark attack while swimming off the beach of Kaanapali in Maui.
The last fatality was a 65-year-old woman snorkeling at Ahihi Kinau Bay on April 29, 2015.
The victim was later identified as a 65-year-old man from California, according to Dan Dennison, a spokesman for the Hawaii Department of Land and Natural Resources.
He was reportedly vacationing with his wife at the time. He was unconscious when rescuers pulled him out of the water and performed CPR on him.
Conditions were described by officials as flat to 1-foot surf with clear waters.
Keller says the victim was missing his left leg from the knee down and skin was torn from his wrist.
"In an island state that's surrounded by water, human and shark conflicts do occur from time to time", DOCARE official Jason Redulla told ABC News Radio. Three swimmers were attacked by a shark in 2018.
A shark killed a man off the coast of Maui on Saturday, May 25, 2019.
"Maui has for some reason been a hot spot in the Hawaiian islands for tiger shark attacks, and I don't think anybody can really say with any certainly why that is".
ISAF said: "The sombre truth is that most of the world's shark populations are in decline, or exist at greatly reduced levels, as a effect of overfishing and habitat loss".
Authorities haven't confirmed the breed of shark involved in the attack.