Annual Great White Shark Migration Along Pacific Coast Makes Scientists Giddy

Great white sharks back in north coast “Red Triangle”

By Peter Fimrite / SFGate / September 22, 2012

Scientists are all but running giddily into the surf with fancy new gadgetry as the annual migration of great white sharks hits full swing along the Pacific coast and reports flood in about finned beasts lurking in shallow waters.

The ferocious predators have returned to their feeding grounds in the so-called Red Triangle, an area roughly between Monterey Bay, the Farallon Islands and Bodega Head, but sharks have been spotted all along the coast, including a 20-footer seen last weekend next to Moss Landing Harbor.

The appearance of the great whites could not come at a better time for researchers, who recently deployed a new robotic device that can identify and track the movements of sharks and other fish equipped with acoustic monitoring devices.

“What we are trying to build right now is a wired ocean with a network of interactive devices that will tell us where the animals are,” said Barbara Block, a professor with the department of biological sciences at Stanford University’s Hopkins Marine Station.

The new robot, called the Wave Glider, is a solar-powered device with a satellite hookup developed by Sunnyvale’s Liquid Robotics. The mobile surfboard-like gadget propels itself using wave energy and carries receivers and a global positioning system.

The remote-controlled device, which is just now returning to San Francisco area waters after a trip up the coast to Oregon, is the latest addition to a growing arsenal of technology that is being used to study sharks. Transmitters have been attached to 100 sharks, and the acoustic pings of predators passing within 1,000 feet are being picked up by receivers affixed to buoys in known shark hangouts.

Monitoring program

Block’s team of eight Stanford scientists has been working with marine biologists at the Monterey Bay Aquarium on the shark-monitoring program, called Tagging of Pacific Predators, or TOPP, for the better part of a decade. It was their landmark study in 2009 that determined that this region’s sharks, known as northeastern Pacific white sharks, are genetically unique compared with other great whites around the world.

The electronic monitoring documented movements from the deep ocean to Northern California in August. Almost all of the white sharks are along the coast by fall, including some that actually enter San Francisco Bay, according to the study.

The sharks begin leaving for a deep ocean spot near Hawaii dubbed the White Shark Cafe in December, according to the study. Female white sharks typically visit the Gulf of the Farallones in alternate years, suggesting that their migration pattern is tied to a two-year reproductive cycle, according to researchers.

It was estimated last year that 220 adult white sharks ply the waters along the Central California coast.

“We’re just talking about adults, which have very regular migratory patterns and return to the same area every year,” said Salvador Jorgensen, a research scientist for the Monterey Bay Aquarium. “There is an unknown number of juveniles and babies … but we don’t know how many there are, because they are not concentrated in one area like the adults are.”

Some of the northeastern Pacific adults also hang out near Guadalupe Island in Mexico. When you add the estimates of these two groups together, it comes to 339, a surprisingly small number given the number of sightings this year. The estimation methods are still being refined, Jorgensen said.

Sharks near shore

A 20-foot shark, one of the biggest ever seen in the area, was reported by a Monterey Bay tour boat company last weekend near the mouth of the Pajaro River.

Sean Van Sommeran, the executive director and founder of the Pelagic Shark Research Foundation in Santa Cruz, photographed the shark near a pod of bottlenose dolphins, less than 200 yards from shore.

He said he also saw a 10- to 12-foot shark that was so close to a pier at Seacliff State Beach, east of Capitola, that “you could have literally cannonballed off the side into the shark.” Van Sommeran said he also spotted a white shark lurking around dolphins off Manresa State Beach last weekend.

“Usually, we see them around dolphins, which is an important safety tip because there are still a lot of people who think dolphins make you safe against sharks,” Van Sommeran said. “These big sharks eat dolphins.”

Close calls

So far this year there have been four reported shark encounters, according to John McCosker, the chairman of aquatic biology at the California Academy of Sciences in San Francisco. The incidents included May attacks on a paddle boarder near Avalon Harbor (Los Angeles County) and a kayaker off Cambria (San Luis Obispo), and the bitings in July of a kayak in Santa Cruz and a surfer at Topanga State Beach (Los Angeles County). None were fatal, he said.

Eleven people have been killed by sharks off the California coast since the first documented attack on a human 59 years ago. The body of a probable 12th victim was never found, so he isn’t counted.

This fall, Stanford and aquarium scientists plan to take DNA samples and affix acoustic tags to at least 30 more sharks. They will also photograph the unique markings on the big fish’s dorsal fins.

Great white sharks, known scientifically as Carcharodon carcharias, average 15 to 16 feet in length but can grow to 20 feet and weigh as much as 4,800 pounds. The biggest one ever recorded was 21 feet long and weighed 7,300 pounds. It was caught in 1939.

Jorgensen said shark researchers have been taking photographs of dorsal fins since 1987 and have gotten so familiar with some sharks that they have named them. One 16-foot shark, named Tom Johnson after the naturalist who first photographed him, has been documented in the region for 26 years, Jorgensen said. He has grown 3 feet in that time and is believed to be over 30 years old.

“Three weeks ago, he returned on schedule to Tomales Point,” Jorgensen said. “This is now the longest studied white shark in the world. Every year, we congratulate him on another successful year.”

 Track sharks yourself

Stanford’s Hopkins Marine Station and the Monterey Bay Aquarium now have an iPhone and iPad app called Shark Net, which people can use to track the great white sharks’ acoustic signals.

Avoiding Attacks

The California Academy of Sciences provides advice to swimmers, surfers, kayakers and divers in how to avoid sharks at calacademy.org.

 Peter Fimrite is a San Francisco Chronicle staff writer. E-mail: pfimrite@sfchronicle.com Twitter: @pfimrite