Few animals garner quite the mix of fascination and terror as the shark — especially during beach season. It’s the subject of novels and movies. It has a whole week dedicated to it, courtesy of the Discovery Channel (although admittedly Shark Week has had its fair share of criticism from scientists). And this year, a spree of shark attacks off the coast of the Carolinas has attracted nationwide media coverage and inspired extra fear in beachgoers.
But it’s not just this summer’s events that have people on edge. In recent decades, the number of reported shark attacks around the world has steadily increased. But while attacks appear to be on the rise, many species of sharks have experienced widespread population declines, leaving experts wondering just what’s going on out there beneath the waves. Now, recent research may help put ocean enthusiasts at ease — even as there are more shark attacks being reported, your individual risk of being bitten by a shark may be much lower than you think. The idea is that, with more people in the water than ever before, the total number of shark attacks is rising — but each person’s risk of being attacked is falling.
A new study, scheduled to publish Friday in the journal Frontiers in Ecology and the Environment, delivers this surprising news: A human’s individual risk of being attacked by a great white shark — the same species made famous by Jaws — off the coast of California has actually decreased by more than 90 percent since the 1950s.
The researchers collected reports of shark attacks along the California coast from a database called the Global Shark Attack File and analyzed them along with public data on changes in California’s coastal population, its annual number of beachgoers and the activities they engage in (such as surfing or swimming) between 1950 and 2013.
They found that, when you compare the number of reported shark attacks each year to the number of people actually in the water and the activities they’re engaging in, an individual person’s risk of being attacked has declined by a whopping 91.24 percent since 1950. “You see that when you take into account all these factors, the chances for any person to get a shark attack declines dramatically,” says Francesco Ferretti, a postdoctoral research fellow at Stanford University’s Hopkins Marine Station.
Furthermore, the researchers found that risk of being attacked changes depending on the season, the coastal region and the activity a person is involved in. Attack rates tend to be highest in October and November, they discovered, and higher in northern California than in southern California. Additionally, abalone divers seemed to be most susceptible to attack, followed by surfers, scuba divers and swimmers. But even for abalone divers, the chance of being attacked in 2013 was only one in 1.44 million.
A major inspiration for conducting the study in the first place was simply to find out more about white sharks, says Ferretti. White sharks are responsible for most documented attacks in California (in very rare cases people have been attacked by other species, including leopard sharks, blue sharks and mako sharks) — but surprisingly little is known about the size of their populations. Some experts believe the shark’s numbers have been increasing in recent years, although there’s not enough concrete evidence to say for sure, says Ferretti. Still, an uncertainty in the white shark’s population health made the study’s dramatic results a bit surprising, the researchers say.
“We actually went in expecting an increase in shark attacks, and that was based on reports of the recovery of white shark populations, as well as the recovery of the prey of white sharks, such as elephant seals,” says Fiorenza Micheli, senior author of the study and professor of biology at Hopkins Marine Station. “So the result that, in fact, they have been declining — these interactions — was a bit surprising to us.”
The results don’t necessarily mean that shark attack rates are declining everywhere, since the study covered only one species in one location. However, “in principle, their results are probably broadly applicable to a lot of other systems,” says James Estes, a professor of ecology and evolutionary biology at the University of California Santa Cruz. (Estes was not involved with the study, but peer reviewed it for Frontiers in Ecology and the Environment.)
There are many other large predators in the world that come into conflict with humans seemingly frequently, such as lions in Africa or bears in North America, Estes says. This study suggests that an increase in the number of reported attacks by these animals does not necessarily mean that a person’s individual risk of being attacked is increasing. More research should be done to understand the statistical likelihood of an encounter with one of these predators and, if the risk is actually declining, what factors are causing this to happen.
The recent Carolina attacks, for instance, have been largely attributed to shark species that are thought to be experiencing population declines, such as bull or tiger sharks. Experts have speculated that the region’s sudden uptick in attacks are caused by environmental factors luring more sharks into the shallow waters, such as changes in ocean salinity or the abundance of fish the sharks eat.
When it comes to the white shark, the researchers agree that more research is necessary to figure out exactly what’s been going on with its populations. There’s a chance that the reason for the decline in attack risk is because white sharks, themselves, are actually growing more scarce. While there is still little known about the white shark’s life history, population declines could be worrisome since large predators often play important roles in their ecosystems, Estes says.
On the other hand, if white sharks have been increasing, as some experts believe, this is good news for both shark conservation and public safety in California. It would mean that attack rates are declining despite increases in shark numbers, suggesting that sharks and humans can coexist with minimal threats to beachgoers.
“The goals of protecting the oceans and increasing public safety, at least in California, seem to be non-mutually exclusive,” Micheli says. In other words, promoting the continued recovery of the species would not necessarily pose an increased risk of attack for humans in the area.
The authors propose several reasons that attacks could be declining despite a population recovery. One idea is that an increase in their natural prey is drawing them away from humans. Elephant seals are a major food source for white sharks, and their populations have been growing steadily during the last few decades, according to the researchers. Their growing presence on the coastline might be drawing sharks away from populated areas and causing them to zero in on seal colonies instead, reducing the chance of encounters with humans.
And other factors could also influence sharks, who tend to gather where conditions are most favorable for them. “The ocean is changing drastically, warming, rising, there is heavy fishing and pollution,” says Salvador Jorgensen, another author on the paper and a research scientist at the Monterey Bay Aquarium with experience tracking white sharks off the California coast. “So we should expect changes in where sharks are concentrating.”
Behavioral changes in humans could also help account for the decline in attack rates, says Ferretti. For instance, people might simply be more savvy than they used to be and more inclined to avoid unnecessarily risky behavior, like swimming at dawn or dusk (prime feeding time for sharks).
Better information on the reasons behind the declines in attacks can be used to promote public safety without resorting to extreme measures, such as culling, or intentionally thinning out shark populations to reduce human risk. For instance, if an increase in shark prey is the key, then more emphasis could be placed on seal conservation in order to keep white sharks well-fed and away from humans.
In the meantime, people should continue to exercise common sense when they visit the beach, Ferretti says. “The point is that shark attacks are really rare events,” he says. “But that doesn’t mean people should not take the due precautions when they go to the ocean.”
Juliet Eilperin contributed to this report.