Statement: “Careful analysis of deaths in the ocean near San Diego shows that on average, the death of each swimmer killed by a shark saves the lives of ten others,” wrote world-renowned scientist Freeman Dyson in the Dec. 22 edition of The New York Review of Books.
Determination: False
Analysis: In his review of a high-profile new book about the illusions we create with our minds, famed physicist Freeman Dyson mentioned research into the effects of fatal shark attacks off San Diego.
Dyson wrote in the The New York Review of Books:
A striking example of availability bias is the fact that sharks save the lives of swimmers. Careful analysis of deaths in the ocean near San Diego shows that on average, the death of each swimmer killed by a shark saves the lives of ten others. Every time a swimmer is killed, the number of deaths by drowning goes down for a few years and then returns to the normal level. The effect occurs because reports of death by shark attack are remembered more vividly than reports of drownings. System One is strongly biased, paying more prompt attention to sharks than to riptides that occur more frequently and may be equally lethal. In this case, System Two probably shares the same bias. Memories of shark attacks are tied to strong emotions and are therefore more available to both systems.
Dyson, who’s retired from a professor position at the Institute for Advanced Study in Princeton, N.J. and who’s in his 80s, is no newcomer to the world of research. A 2009 New York Times article described him as a “world-renowned scientist and public intellectual,” a man who “contributed seminal work to physics by unifying quantum and electrodynamic theory.” Most recently, he made waves by doubting the threat of global warming.
So is he right? Is there research linking fatal shark attacks to fewer drownings?
Internet searches don’t turn up any sign of such a study. Even if there was a study of the aftermath of fatal shark attacks in the ocean near San Diego, it would be quite limited for a simple reason: No more than two or three people have been killed by sharks in the recorded history of the county.
One attack occurred near La Jolla Cove in 1959, when a 33-year-old man was killed by a shark while diving for abalone. In the spring of 2008, a shark attacked and killed a 66-year-old man as he swam with a group of triathletes in the waters off Solana Beach.
Authorities said a third fatal shark attack occurred in 1994, when a 25-year-old woman was found dead in the water near Point Loma. But there’s a dispute over whether she may have actually been murdered and dumped in the ocean.
Statistics regarding ocean drownings in the years after the 1959 attack weren’t immediately available. But I was able to track down the numbers of drownings in the years around the 1994 incident and the 2008 attack. They allow us to see if drownings in the ocean off city beaches did indeed fall after fatal shark attacks.
There were 4 ocean drownings in 1993, 9 in 1994 (the year of the reported attack), 3 in 1995 and 10 in 1996. In 2007, there were 3 drowning deaths, followed by 2 in 2008 (when the fatal attack occurred up the coast off Solana Beach), 2 in 2009 and 7 in 2010.
Dyson wrote that “every time a swimmer is killed, the number of deaths by drowning goes down for a few years and then returns to the normal level.” But the available statistics from 1993-1996 and 2007-2010 don’t indicate any such trend. In fact, the number of drownings rose to their highest level in years in 1996 (two years after the 1994 incident) and in 2010 (two years after the fatal attack).
It’s possible that drowning statistics for beaches in other parts of the county reveal different trends. But the claim specifically refers to San Diego.
So where did Dyson get his information? I asked him by email. He replied: “Sorry I cannot document my story about sharks. I heard the story when I was living in San Diego some years ago and I have no record of the source. I should have said it was an urban legend rather than a scientific fact.”
To put it all together: Drowning statistics don’t support Dyson’s claim that drowning rates have fallen in San Diego after fatal shark attacks. Dyson himself admitted that he has no documentation to validate his claim. Since nothing supports it and the available evidence debunks it, the claim is false.
CORRECTION: We incorrectly described Freeman Dyson as a former Princeton University professor in the original story. In fact, he is retired from a professor position at the Institute for Advanced Study in Princeton, N.J. We regret the error.
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Please contact Randy Dotinga directly at randydotinga@gmail.com and follow him on Twitter: twitter.com/rdotinga.