Stanford study maps white shark behavior to understand attack risk factors

July 29, 2015, 10:38 p.m.

Although the number of white shark attacks per year in California has increased since the 60s, the risk of an individual being attacked by a white shark has decreased by 91 percent, according to a recent study by Stanford researchers and other scientists.

“Even in the possible situation that white sharks may be recovering, we quantified how many ocean goers there have been [in California], and taking that number into account, the risk of being attacked has decreased,” said Francesco Ferretti, lead author and postdoctoral scholar at Hopkins Marine Center.

The study, to be published in the journal Frontiers in Ecology and the Environment, is an effort to increase public understanding of behavioral and migratory patterns of white sharks, or “great whites,” the species most involved with shark attacks in California. Its authors believe that this rise in understanding will help reduce the risk of shark attacks, and the paper will be published at the end of July.

Researchers explained that location and timing are key factors for shark attack risk. For example, the likelihood of an attack while surfing on the Mendocino County Coast in October is more than 1600 times greater than the risk while surfing between San Diego and Los Angeles in March.

The researchers have proposed two possible causes for the decrease in the number of attacks: that the number of white sharks has declined or that shark behavior has changed in recent years. Researchers do not have enough data to confirm declining population numbers, however, and have leaned toward the latter hypothesis.

In 1970, the federal government issued the Marine Mammal Protection Act, which has helped save seals and sea lions, the main diet of the white shark, from near extinction.

“[Sharks] are less likely to bump into people when they’re doing their business in the ocean,” said Salvador Jorgensen, co-author and Monterey Bay Aquarium research scientist. “As the prey increases, the sharks are more focused on that area and less focused on beaches where people go.”

Although some governments, including those in Hawaii and Australia, have attempted to reduce shark attacks by “culling,” or killing sharks, the authors explained that this destructive tactic actually has no effect in reducing attacks.

“If you kill a thousand sharks, a thousand more will move in [that area] because it’s open space,” Jorgensen said.

To preserve the white shark population and also reduce the number of attacks, the authors hope that their data will alleviate misconceptions about sharks and help ocean-bound visitors make more informed decisions.

“Not having a complete control of the [ocean] environment increases our fear [of sharks],” Ferretti said. “By knowing the ecology of the [white shark] species and the distribution, we can increase the safety of people.”
Contact Kalpana Gopalkrishnan at kalpanagk1999 ‘at’

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