Swimmer fends off shark with diving knife as Hawaii officials report second attack in less than a week

For the second time in less than a week, Hawaii officials put up shark warning signs after a shark bit a man Tuesday. The man, a 68-year-old from Waikoloa, was swimming about 400 yards from shore at Anaehoomalu Bay on the Big Island when he was bitten on the lower left torso, Hawaii county police said.

"The swimmer attempted to fend off the shark with a diving knife and the shark released the swimmer," police said in a news release.

The man was taken to an island hospital. He was in stable condition and was to be transported to Oahu for treatment of injuries that were not life-threatening, police said.

The state Department of Land and Natural Resources said the tiger shark was reported to be 12 feet long.

Witnesses told Hawaii News Now the shark "got a good chunk of the left side of his back rear."

"It was hectic," witness Anthony Singh told the station. "It was brutal."

Warning signs subsequently went up at the bay in Waikoloa, a resort area.

Shark signs were previously posted last Thursday off southern Maui after a 60-year-old woman visiting from Washington state disappeared while snorkeling. Her husband and witnesses told officials she was attacked by a shark. The search of the area around Keawakapu Point was called off Friday.

The incidents come three months after a woman suffered a "serious" shark bite in a bay on Maui's north shore.  

Research published last year showed that shark attacks against the humans are often a result of mistaken identity.  Sharks, according to the research, have limited color perception if they are not completely color blind, and have spatial resolving power that is "considerably worse than humans." So when they are looking for prey, researchers found, they more heavily rely on motion and brightness contrast. 

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