For Sean Van Sommeran, the term "swimming with sharks" is more than a metaphor.

As a kid, the "Undersea Kingdom" addict would stuff his pockets full of squid, scan the waters near Capitola Wharf, then dive in above a pool of leopard sharks, hoping to make contact. In a way, Van Sommeran's job today is merely a continuation of that quest.

"I've always had this very basic, very puerile fascination with sharks," he said.

Except now, a little older and wiser at age 41, that quest is fueled by a passion to protect a misunderstood fish whose populations are rapidly declining. A decade ago, this passion spurred the short, burly fisherman with a baby face to form the Pelagic Shark Research Foundation, a Santa Cruz nonprofit that promotes research and conservation.

"It became abundantly clear to me that the best way to defend these animals was to collect data on them and to help people understand the history of the animal," Van Sommeran said. "I dropped everything and began to work on this."

After years of toil on a shoestring budget the persistent -- and stubborn -- Van Sommeran, who never finished college and bills himself as a sort of blue-collar scientist, has turned his foundation into one of the nation's most visible shark advocacy groups, featured in publications such as Time, Discover and National Geographic. Van Sommeran and his staff -- a handful of volunteers with day jobs in the marine sciences who moonlight as Pelagic field researchers -- are also the people to whom many academics turn for field research in today's leading shark studies.

The team includes everyone from a professional diver and marine biologist to a surfing instructor and fisherman. In addition, Pelagic is aided by about two dozen undergraduate and graduate students each year through a springtime course it offers on scientific sampling.

Much of Pelagic's research and advocacy has been funded out of his own pocket, and Van Sommeran works long hours most of the year -- chartering boats and as a naturalist field guide -- to save up money to work full time at Pelagic when sharks migrate in the fall. Pelagic survives on a budget that tops $20,000 in a good year, but is often as low as $12,000.

Van Sommeran and Operations Director Callaghan Fritz-Cope often pay for field expenses. The pair tries to bring in extra cash by filming documentary footage for venues like the Discovery Channel and National Geographic, and giving talks in classrooms and museums. In addition, Van Sommeran sometimes earns money doing undercover investigations into activities like turtle poaching and shark "finning," whereby the sharks' fins are cut off and their carcasses thrown back into the ocean.

Monitoring the sharks

Cruising the Monterey Bay in their sportfishing and scuba-diving vessels, Van Sommeran's scientists tag sharks to help keep track of populations, collect tissue samples for DNA studies, and, at Aņo Nuevo island, place satellite transmitters on great whites to study migration patterns.

The transmitters have recorded groundbreaking data that show sharks migrate as far as Hawaii during the spring. At the Elkhorn Slough near Moss Landing, Pelagic monitors leopard, thornback ray and other sharks, unraveling the mystery behind their breeding and foraging behaviors.

Just last month, Van Sommeran and Fritz-Cope made a grueling, 250-mile trip in their 26-foot boat to the Isla Guadalupe near Baja, Mexico, to study the seal rookery where sharks tagged at Aņo Nuevo have been found migrating. Pelagic plans to set up a field research base at the island within the coming year.

Van Sommeran has been a leader in efforts to enact regulations protecting the wide variety of sharks that populate the California coast. But with species such as the basking shark yet to receive protection and with fishing for shark-fin cartilage -- an Asian delicacy -- on the rise, Van Sommeran says he still has a lot of work before him.

"Sometimes, I can't sleep at night. My heart just goes thump-uh-thump-uh- thump thinking of all that's at stake," he said.

The world's largest predatory fish, reaching up to 21 feet in length and 4,800 pounds, the great white shark is one of the least understood creatures - - largely because it's so hard to study. Contrary to their portrayal as vicious man-eaters, most sharks are indifferent to humans, preferring the dense energy source that blubber-rich seals and sea lions provide -- half a seal can sustain a shark for more than a month.

Region's 'Red Triangle'

In addition to the coasts of South Africa, Japan, southern Australia and the northeastern United States, the great white is found in large numbers in the "Red Triangle" -- a 100-mile strip of California coast stretching south from Bodega Bay to Monterey, where the shark's prey, the elephant seal, is in abundance. Some estimates put the number of great whites here at 100 to 300.

Since the 1930s, when they were exploited for their liver oil, sharks have been victims of heavy overfishing. Bowls of shark-fin soup sell for as much as $100, and a single fin can fetch as much as $20,000. The lucrative trade accounts for an estimated 100 million shark deaths a year and encourages finning, according to www.nature.com. The practice has been prohibited in the United States since 2000.

Millions of sharks also die each year from getting tangled in fishing nets set for tuna or billfish. Recreational sport has taken its toll as well. As late as the mid-1990s, for example, sport fishermen slaughtered as many sharks as they could fit into a day during an annual shark derby at the Elkhorn Slough. In the 1920s, Monterey Yacht Club guests could harpoon a shark for just 50 cents.

Recent studies have discovered shark populations are declining at shocking rates. North Atlantic shark populations have been cut in half over the past 15 years, with some species so low they may soon be wiped out, according to researchers at Dalhousie University in Nova Scotia. Hammerhead, thresher, white and blue sharks in particular are going fast, the researchers found. The World Conservation Union considers white sharks to be threatened globally.

Except for regulations protecting the great white and bag limits for sport fisherman, there are few regulations -- especially when it comes to commercial fishing -- for sharks on the West Coast, Van Sommeran said. Conversely, an East Coast management plan developed by the National Marine Fisheries Service has protected 39 species of sharks since 1993. Regulations worldwide are likewise patchy.

Little data available

The disparity is largely due to a dearth of baseline shark data. The Dalhousie University study, published in January, represented the first definitive numbers on shark populations -- and even those are questioned by some people in the fishing industry, who say the information is incomplete and full of errors.

Researchers got their data from analyzing logbooks recorded from 1986 through 2000 by fishermen and biologists on board longline fishing vessels. Fishing industry people said sharks roam long distances and are often outside the regions where vessels record their numbers. They also said the logbooks analyzed are often inconsistent and unreliable.

Pelagic is among a handful of California researchers and biologists compiling shark data that could prove integral to enacting strong protective measures. Others include scientists at UC Davis; California State University, Long Beach; Hopkins Marine Station at the Monterey Bay Aquarium; and the Point Reyes Bird Observatory at the Farallon Islands.

Pelagic was one of the first to start ID tagging the 21 species of shark that populate Monterey Bay, and has tagged more than 1,500 sharks since its inception, according to Van Sommeran.

The tagging is instrumental in helping determine population counts and learning about sharks' life history. Sharks tagged by Pelagic have been recovered from Dana Point and the Channel Islands to Mexico. One blue shark was discovered off the coast of Japan.

In addition, tissue samples taken while tagging have helped a researcher at Southeastern University in Florida develop a DNA test that identifies where shark fins on the global market are coming from. The test could be used to help crack down on illegal finners.

Pelagic tags the sharks with a unique process that combines lures with bait and avoids cages. At Aņo Nuevo, a seal-shaped piece of plywood is attached to a fishing rod and cast out near the rocky hauls or landings used by the roughly 8,000 elephant seals that populate the island from December to March.

Then a 15-pound slab of blubber is soaked in the water to add a scent to accompany the lure. Within as little as a minute to as long as several hours a great white shark will approach the lure, usually nudging it and occasionally biting it.

Crew members reel the lure in to get the shark within reach of a lance, on whose tip sits a tag or biopsy instrument, and pierce the shark at the skin behind its dorsal fin. The crew guides the animal by the nose to strategically position it, hands inching dangerously close to the creature's mammoth jaws. In the open sea, smaller sharks are lured with salmon or tuna, and then scooped up with a long-handled sport fishing net.

The foundation's tracking of sharks sometimes resembles a real-life version of the game "Submarine." In 1997, Pelagic attached acoustic transmitters to great whites at Aņo Nuevo that allowed researchers to keep simultaneous track of five sharks for 10 hours a day -- no small feat. The transmitters, which emit radio signals, worked in conjunction with "sonobuoys" -- buoys equipped with underwater microphones -- that detected the transmitters' "ping-ping" whenever sharks came within range. Pelagic also helped run the island-based computer station that recorded the transmitters' signals.

How sharks hunt

The tracking shattered myths about shark behavior such as the belief that great whites hunt only in the daytime. It also showed white sharks are tactical hunters -- often ambushing seals -- as well as social animals who like to hang out in shark cliques.

"(The study) never would have been done without them," Peter Klimley, the UC Davis ichthyologist who led the study, said about Pelagic.

Pelagic's satellite tagging has produced even more startling results. In 2000, the foundation, along with biologists at the Point Reyes Bird Observatory, attached so-called "smart tags" to great whites that recorded groundbreaking data about shark migration. The tags recorded snapshots of the sharks' water depth, position, speed and more every two hours. The tags pop off at programmed times and float to the surface, where satellites upload the recorded data, which is in turn downloaded to land-based computers.

The research revealed that great whites, after leaving the California coast in the winter, travel much vaster distances at far greater depths than previously thought. Contrary to popular theory, which held that sharks spent most of their time close to shore hunting seals and sea lions, smart tags showed sharks traveling as far as Hawaii and to subtropical regions in the eastern Pacific. The sharks often swam 1,000 feet or more below the water surface and sometimes dove deeper than 2,000 feet, spending several months in the open sea.

The new information, combined with future tracking, could be used to help enact regulations protecting pupping grounds, as it suggests females may be traveling to the eastern Pacific to give birth. Pelagic placed transmitters on four more sharks last season and plans to target pregnant females this year.

Pelagic's success in the field has not come without controversy. Behind the magazine spreads has boiled an academic feud that turns Van Sommeran's cheeks red with anger whenever he speaks of it.

On one side stands Van Sommeran, a working-class stiff fighting for legitimacy in academia, which refuses to take him seriously, he says. He points as proof to the 2002 Nature article chronicling the results of the smart tag study. The academic paper, written by researchers at Stanford University and UC Santa Cruz, failed to even mention Pelagic's role in the field, despite giving a co-authorship to Farallon biologists who played a similar role. The issue is in litigation.

Klimley says Van Sommeran rightly bears a grudge.

"I think he did more work for (the Nature) paper than some who were an author on it," said Klimley, who did not participate in the study. "I would have included him (as coauthor) if I were senior author."

Grabbing for attention?

But Klimley also said that tagging a shark does not make Van Sommeran a scientist, and faulted him for sometimes hogging the media and diverting attention from the people who "really do the work."

"To be honest, Sean is not a researcher... he doesn't have the scientific skills and hence has not published on his own," Klimley said. "Putting a tag on a shark is a relatively easy thing to do."

Burney Le Boeuf, a UC Santa Cruz seal expert who participated in the Nature study, refused to even comment on Van Sommeran's legitimacy as a researcher, because Le Boeuf said he had nothing good to say about the matter.

With Van Sommeran not short on braggadocio -- he claims, for example, he knows more about California sharks than anyone -- it's hard to know whose side to take. Van Sommeran boasts "these Ph.D.s are sick of me proving them wrong" and seems proud that "I've made enemies with everybody."

Whatever the case, most agree Van Sommeran deserves kudos for his work as an advocate for shark conservation, said Klimley, who describes Van Sommeran as a "folk hero" to local surfing and fishing communities.

"Sean's value is more as a promoter of shark research," he said. "Sean has been a great popularizer of sharks and that's his strength, not as a scientist."

Van Sommeran plans to continue dedicating his life to the animal that caught his fancy as a kid.

A man who thinks of humans "as these big fire-making mobs who run buffalos over cliffs," Van Sommeran considers himself foremost an environmentalist. But he admits he is also a man with a short attention span who needs work that keeps him on his feet.

"I'm just so stoked to be living in such close quarters to such an amazing creature. It helps to inspire me daily," he says, pausing for a sly grin, "partially just to confound my foes."

E-mail comments to penfriday@sfchronicle.com.

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