White shark and schooling bigeye trevally.
White shark and schooling bigeye trevally.
It seems that the United States is in the midst of a shark frenzy that has seen a spike of reported attacks on both coasts recently. The frenzy, however, appears to be more a product of increased media exposure and ocean recreation than an actual uptick in the risk of shark encounters, according to a new study led by Stanford and supported by the Lenfest Ocean Program.
The study, published on July 9th in Frontiers in Ecology and the Environment, reviewed data from 1950 to 2013 and found that despite increasing reports of shark attacks—mostly by white shark—in California, the individual attack risk has dropped by more than 91 percent in the last six decades. Rather than cull sharks—which previous research shows has no effect on risk of encounters—resource managers should promote safe use of the ocean by providing information on how risk can vary among locations and times, according to the study.
"Our results indicate that the seemingly conflicting goals of protecting large predators and people can be reconciled,” said co-author Fiorenza Micheli, the David and Lucile Packard Professor of Marine Science at Stanford’s Hopkins Marine Station and a senior fellow at the Stanford Woods Institute for the Environment. “An awareness of risk—in places and times of the year—can greatly increase the safety of ocean users.”
The researchers speculate that more frequent reports of shark attacks could be due to factors such as increased human population and ocean recreation, as well as more widespread media coverage. The decline in actual risk may be due to factors such as drops in global shark populations or changes in the spatial distribution of people and sharks.
Why Sharks and Other Large Predators are Critical
Sharks play a vital role in marine ecosystems, and likely benefit people. For example, research linked a drop in shark numbers to the collapse of a North Carolina bay scallop fishery due to a population boom of scallop-eating rays normally controlled by sharks. Other research shows that the presence of tiger sharks, the natural predator of grazing animals such as sea turtles and dugongs, prevents overgrazing of seagrass and helping to maintain this coastal ecosystem.
The study’s results suggest that healthier ecosystems may be safer when it comes to human-shark interaction. In California, for example, the recovery of elephant seals has concentrated sharks around seal colonies and away from human beachgoers.
White shark approaching kayaker in Mossel Bay, South Africa.
Chances of a Shark Encounter and How to Avoid One
The chances of getting attacked by a shark are exceedingly slim, according to the study:
Those entering the ocean should avoid locations and seasons where risk is highest, the study’s authors advise. For example, the riskiest time and place for California surfers is October and November in Mendocino County. That risk can be reduced 25-fold if you surf in March, and more than 1,600-fold if you surf in March between San Diego and Los Angeles.
Coauthors of “Reconciling Predator Conservation with Public Safety,” include Salvador Jorgensen of the Monterey Bay Aquarium; Taylor K Chapple of Hopkins Marine Station; and Giulio De Leo, a Stanford professor of biology and senior fellow at the Stanford Woods Institute for the Environment. The research was funded by the Lenfest Ocean Program.