The dolphin had been calm near shore where people waded in to try to help it, but it later became agitated by what observers believed was a nearby shark. The dolphin swam away weakly, said David Schofield, Pacific island marine mammal response coordinator for the National Oceanic and Atmospheric Administration.

The first report of the stranded dolphin came around 8 a.m., he said.

When federal marine officials later arrived at the scene, the dolphin was being supported by people in the water, Schofield said.

People are normally not supposed to be in such close proximity to a dolphin, but the animal had attempted to beach itself four times, and it was listing to its left side, suggesting it possibly had a respiratory problem or infection, he said.

"If it wasn't supported, it would roll over and obstruct its blowhole," Schofield said.

Renee Gillett of Langley, British Columbia, said she and her husband, Stu, were on a morning walk when they saw people helping the large dolphin near the shoreline. They helped hold the dolphin and were some of the last to leave the water after the shark was sighted.

"When we came, she was completely on her side and then she turned completely over," Renee Gillett said.

She said other volunteers attempted to release the dolphin four times, but the sick or injured animal circled back toward shore each time.

After laying docile for about four hours, the dolphin became restless.

Observers in the water attributed the dolphin's change in behavior to the presence of a shark in the water.

They reported that the dolphin began slapping its tail fluke and thrashing after 15 minutes of restlessness, and that was about the same time the shark was spotted by two people.

Officials on the beach advised those in the water to let the dolphin go and they headed to shore.

Schofield said federal officials chose to be cautious.

"We didn't want people to get attacked by sharks," he said.

Kihei resident Rod Quigley said: "The dolphin itself knew the shark was there. ... She was pretty docile there for quite a while and then she started getting agitated."

Quigley said he could not say what kind of shark it was or how big it was.

"All I know, it was a dorsal fin, and it was coming toward us," he said.

Schofield said the dolphin swam away around 11:30 a.m. He estimated it was 7 to 8 feet long.

It left the area before mammal experts could determine its gender.

Risso's dolphins are known to be in Hawaiian waters, but the species is not common, Schofield said.

Risso's dolphins are typically 10 feet long, but some of the animals have been measured as much as 12? feet long. The adult animals weigh about 650 pounds on average, but they can tip scales at as much as 1,100 pounds.