Commercial fishing by U.S. and Mexican vessels is the primary threat to great white sharks in this area, the scientific petition by the groups Oceana, Center for Biological Diversity and Shark Stewards said.

The request for federal protection was filed Monday with the U.S. National Marine Fisheries Service in Washington, with a second petition to be filed this week under California's Endangered Species Act, Geoff Shester of Oceana said in a telephone interview.

Until last year, there was no way to tell how many great white sharks lived off the coast of California, Baja California and Mexico, Shester said on Wednesday.

In 2011, two studies of this population of great white sharks in the Pacific found it to be genetically distinct and isolated from other groups of these creatures around the globe, he said. The studies estimated there are fewer than 350 adult and sub-adults in these waters.

Although there is no way to know how many sharks were in the area previously, it is known that their main prey - California sea lions, harbor seals and elephant seals - were depleted by human exploitation in the 1700s and 1800s, according to Shester.

While the seal and sea lion populations have rebounded, it will probably take great white sharks longer to do so, because this species grows slowly and most great whites do not reproduce until the age of 10 years and have few young.

The low estimate for the great white shark population off the West Coast makes the group inherently vulnerable, said Shester, Oceana's California program director.

A total population of 350 means there are probably fewer than 100 breeding females, he said. This would make it challenging for the great white shark population to rebuild.

If this group of sharks went extinct, he said, other groups would survive, but these animals would be gone from the North American West Coast for centuries or millennia, because this population does not commingle with other groups.

"These are iconic top predators that are basically keeping the entire food web of our ocean in check," Shester said. "They regulate populations of seals and sea lions and that benefits entire ecosystem including our fisheries. Ultimately the loss of top predators like sharks could have disastrous consequences for oceans and coastal economies that depend on it." (Reporting by Deborah Zabarenko, Environment Correspondent; Editing by Jackie Frank)

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