Shark sightings on O'ahu's North Shore have hit a three-year high so far this year, with more than twice the number of shark encounters and sightings as the surfing mecca had in all of 2005.

Surfers, swimmers and beach-goers have reported seeing more sharks cruising the shores of Waimea Bay, invading surf lineups at other beaches, and snatching sea turtles from the ocean.

"In my almost 40 years of surfing on the North Shore, this is the most shark sightings and encounters I have heard of," said resident Mike Takahashi, who is worried about the safety of his ocean-active family.

A North Shore spearfisher and a surfer have been bitten in separate shark attacks. That compares to one similar incident on the North Shore last year, and none during the previous seven years.

"I can tell you there have been a lot more confirmed cases this year than last year — or any other year for that matter," said veteran North Shore lifeguard Capt. Bodo Van Der Leeden of the city's Ocean Safety/Lifeguard Division.

"This year, we've had more than a dozen shark sightings and encounters. In 2005 we had a half dozen. In 2004 we had two or three."

Van Der Leeden said these things seem to run in cycles. He recalls a rash of similar sightings, encounters and attacks and one death in the early 1990s.

But, "there's even more now. We're hearing it from surfers we know we can trust. And quite a few have been witnessed by lifeguards."

Ralph Goto, water safety administrator with the city's Ocean Safety Division, said a sighting doesn't necessarily mean a particular type of shark was in the water.

If the sighting is confirmed, the city along with the state Department of Land and Natural Resources will post warning signs, he said. Confirmed sightings normally come from lifeguards or other reliable sources such as fishermen or divers.

About a month after former lifeguard Michael Cheape helped respond to the spearfisher who was bitten on May 31, he had his own close encounter with what looked like an 8- to 10-foot tiger shark near Waimea Bay.

"I was on a 12-foot paddleboard and I looked at the right, and about 2 feet below the surface I could see the head coming at me."

An instant later, the shark had flipped him over and knocked him off the board. It was deliberate, said Cheape, who got back on the board and paddled to safety.

Lifelong North Shore resident Alan Sitt lives across from Sunset Beach and said he has heard about more shark sightings in the past year than he has in his whole life.

Last week, one of Sitt's friends was paddling at Kammieland and saw a shark appear nearby and snatch a sea turtle from the water (one of three such turtle incidents reported to Van Der Leeden in the past two months).

Why so many shark sightings?

"When people start seeing sharks, the word gets out and people start looking for them," said shark expert Randy Honebrink of the state Department of Land and Natural Resources' Division of Aquatic Resources. "And the more you look for them, the more you see them."

During the 1990s, a shark sighting hot line had more reports when sharks were in the news and fewer when they were not, Honebrink said.

"We know that sharks are out there, and the fact that someone saw something doesn't really mean anything. There is no correlation between sightings and reports of bites," Honebrink said.

Although Honebrink opposes feeding sharks, he has doubts that the North Shore's two tour companies have much to do with the increased shark sightings.

Neither does Jimmy Hall, owner of Hawaii Shark Encounters. The company has guides with several years of experience in the business.

For about $100 a trip, Hall's company puts shark-watching snorklers in a steel cage about three miles off shore, where the water is 500 feet deep. Once the snorklers are in the cage, the company tosses bait into the water and soon, the snorklers are surrounded by sharks, mainly Galapagos and sand bar sharks.

"If anything, we'd be attracting sharks away from the shore," said Hall, who insists his tour boats couldn't possibly influence the behavior of sharks seen closer to shore.

Sylvia Thompson of Tucson, Ariz., took the tour recently and found it fascinating. The sharks were not aggressive, Thompson said, and there was never a sense that she was in danger.

"I know the debate is going on — that the food is bringing the sharks closer to shore, and there are some who say it desensitizes sharks to humans," she said.

But she said tour people told her crabbers have been throwing scraps in the same waters for 40 years, and it hasn't affected shark activities nearer to shore.

Honebrink said it's difficult to figure what causes sharks to come around. But he said there's a good chance they'll go away again.

"Sometimes you have years when more people get bit," he said. "Sometimes you have years when people see more sharks.

"And then, it just kind of goes back to normal again. That's just what happens. I don't know that there's any way to explain it."

Reach Will Hoover at whoover@honoluluadvertiser.com.