Advisory issued as great white sharks are reported off La Jolla coast

Lifeguards are urging caution after half a dozen great white shark sightings have been reported along the Southern California coast in the last week, but experts downplayed the risk of attacks on humans, saying there is no cause for alarm.

San Diego lifeguards issued a warning Sunday for two miles of coastline from La Jolla Cove to Scripps Pier after a kayaker reported seeing what appeared to be a large great white swimming off La Jolla Shores. Later that day, lifeguards spotted a shark’s 20-inch dorsal fin sticking out of the water about 50 yards from the beach.

“We didn’t close the beach, we just let people know — the scuba divers, kayakers and swimmers — that there’s been shark sightings and just use your own judgment on whether to go out or not,” said Maurice Luque, a spokesman for the San Diego Fire-Rescue Department.

The advisory will expire Tuesday if no additional shark sightings are verified by lifeguards.

La Jolla’s is the latest in a string of shark sightings, ushered in last week when surfer Chuck Patterson shot video of a pair of great whites circling his paddle board in the waters off San Onofre. The clip has garnered hundreds of thousands of viewers online and has been aired on national newscasts.

Aquarium researchers later identified one of the sharks as one they had tagged and released for a tracking study.

Witnesses have reported half a dozen great white shark sightings in the last week at Sunset State Beach, San Onofre and La Jolla, according to the Shark Research Committee, a nonprofit that logs shark reports on its website.

But experts stress that reports of great whites often prove to be false or misidentified. Great whites attract a lot of attention, even hysteria, but attacks are exceedingly rare.

The last known fatal shark attack on the West Coast was in April 2008, when 66-year-old triathlete Dave Martin was killed while swimming near Fletcher Cove in Solana Beach. That attack, thought to be by a great white, prompted authorities to close eight miles of coast for several days.

Although they are found in oceans worldwide, great whites are one of the least understood sharks. Researchers do not know how many of them exist or how far they travel, but satellite tracking studies are yielding some clues.

As far as researchers can tell, Southern California is a nursery ground for juvenile sharks measuring between 4 and 10 feet. Sharks of that age hunt mostly fish, so there’s little danger of the creatures mistaking swimmers for seals or porpoises, as is thought to be the case when full-grown great whites attack humans.

“You talk to most surfers up and down the coast and they see them on a pretty regular basis,” said Andrew Nosal, a shark researcher at the Scripps Institution of Oceanography. “They just don’t report that because it’s a pretty regular occurrence and they don’t think much of it.”

tony.barboza@latimes.com