Willis McInnis, 57, was helped out of the water, but died on the shore despite rescue efforts by beachgoers, police and paramedics. He was bitten in the leg and suffered severe blood loss, police Capt. Charles Hirata said.
"The noises I heard in the water I thought were just him hootin' and hollerin' like he usually does and it turned out it was a cry for help," fellow surfer Tina Cooper told CBS affiliate KGMB. But "the closer I got I saw his leg was pretty mangled, lots of flesh showing."
Hirata said the bite on McInnis was 12 to 14 inches wide.
"It has to be a fairly good size shark to do that damage," said Randy Honebrink, spokesman for the Shark Task Force of the state Department of Land and Natural Resources.
One witness told police the surfer missed catching a wave, turned back out and was paddling when the attack occurred. He was attacked about 300 yards off Kahana beach on Maui's western shoreline.
Dozens of misty-eyed mourners gathered before sunset to join hands at Maui's Pohaku Beach Park, to pray for one of their own. A bench served as an impromptu memorial of tropical flowers with a lei-draped cross and photos of a fallen friend.
"All the guys that surf here know what a happy guy he was," said Cooper
Only four shark attacks were reported in Hawaii last year, including one in October off the island of Kauai that took the left arm of top amateur surfer Bethany Hamilton, then 13.
The last confirmed shark attack death in Hawaii was in 1992 when 18-year-old surfer Aaron Romento of Pearl City was attacked off West Oahu.
Honebrink said there are an average of about four shark attacks off the Hawaiian Islands every year. He said tiger sharks are the most common.
"They do feed an awful lot at things at the surface," Honebrink said. "They have a nonspecific diet, they'll eat just about anything."
Authorities will try to determine the type of shark in Wednesday's attack by studying the victim's bite marks.