Brendan Keaney was sitting on his 9-foot longboard in the water off Waikiki on Sunday when he saw a tiger shark inches below his foot.

“Big blunt head,” he said. “You could see the stripes. It just kind of took a second to realize what it was, and (I)basically jumped on my board real quick and got out of there.”

Although the 5- to 6-foot predator was nonaggressive and already passing Keaney when he noticed it, the 39-year-old surfer decided he was finished for the day.

The shark was one of two seen off Waikiki on Sunday, prompting lifeguards to post shark warning signs at Kaimana Beach and near Duke’s Waikiki, said city lifeguards spokeswoman Shayne Enright.

Beachgoers spotted the first shark about 200 yards off Duke’s at about 9:50 a.m., Enright said.

The shark, which was about 8 to 10 feet, also was nonaggressive. Lifeguards confirmed the sighting and posted signs in the area.

Keaney saw the second shark shortly before noon at Old Man’s surf spot, about 300 yards off Kaimana Beach. A lifeguard told him two other people also spotted a shark in the area.

Keaney recalled seeing tiger sharks while working on snorkel boats off Maui and said he could easily recognize the characteristics of the tiger shark Sunday.

He said the shark was heading toward Diamond Head in about 8 feet of water; about a dozen people were in the area at the time.

There has never been a recorded shark attack in Waikiki, but Oahu has had a spate of them lately.

On Oct. 17 a 44-year-old man was injured by a shark while swimming from the Mokulua Islands and was taken in critical condition to a hospital.

Eight days before that a 25-year-old man lost his lower left leg to a shark bite while surfing at Leftovers on the North Shore.

And about three weeks before that, a man was bitten on the leg by a tiger shark while spearfishing off the north shore of Hawaii island.

So far this year, there have been five shark-related injuries around the main Hawaiian Islands, including a fatal one off Maui in April.

Andrew Price of Diamond Head said Sunday’s sightings were a good chance to remind tourists that there are sharks in the water, but not something one should worry about because more people die from bee stings than shark attacks.

“It’s the ocean,” he said. “There are sharks out there.”

Carl Meyer, a University of Hawaii marine biologist who studies tiger shark movements, said in a post to UH’s website last week that the growing number of ocean users is the single most likely reason for the higher number of shark bites in recent years.

And the fall season usually sees a spike in incidents; nearly one-third of all shark bites in Hawaii occur in October and November, he said.

While the reason for the fall spike is still being researched, scientists suspect it may be tied to the tiger shark’s fall pupping season and greater feeding activity by females.