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A more accurate shark attack risk

mauprietomauprieto New Orleans, LAMember
edited October 2015 in General Discussion

"I like my odds. It's more likely I'll get struck by lighting, so I'm not really worried", says a swimmer in San Francisco interviewed after a white shark was captured on video attacking a sea lion right next to Alcatraz. All over the place you can read about that the risk of dying from a shark attack is 1 in 3.75 million, and how this compares favourably versus dying from being struck by lighting (1 in 79.000), falling (1 in 218), flu (1 in 63), stroke (1 in 24), cancer (1 in 7), etc… (Source: Florida Museum of Natural History))

Taking a larger timeframe and worldwide data (the odds above were using US data), I come up with this:

  • 70 shark attacks per year worldwide (Note 1), or 5250 over a 75 year lifetime. With a worldwide population of 7 billion, the odds of being attacked by a shark is 1 in 1.3 million.
  • 5.9 fatal shark attacks per year worldwide (Note 1), or 442 over a 75 year lifetime. With a worldwide population of 7 billion, there is the odds of dying from a shark attack is 1 in 15 million.

However, 1 in 15 million is NOT the odds if you are an ocean swimmer in San Francisco. As opposed to other causes of death, the risk is not evenly distributed among the total population. The odds above are misleading, since the vast majority of the population has 0 risk of being attacked by a shark. The risk is fully concentrated on those individuals that swim/surf/dive in waters where Great Whites (and Tiger and Bull sharks) frequent.

So, what’s the risk of dying from a shark attack if you are a San Francisco ocean swimmer?

  • Over a 75 year lifetime, there will be 232 shark attacks in CA, 23 of them fatal (Note 1)
  • Over a 75 year lifetime, there will be 4.3 shark attacks to SF swimmers, 1 of them fatal (Note 3).
  • There are 1750 ocean swimmers in SF (Note 4), so these individuals (including myself) have a 1 in 1750 chance of dying from a shark attack over their 75 year lifetime (or, put it another way, 1 SF swimmer would die every 75 years from a shark attack).

The numbers will vary depending on many other factors and assumptions, but the main point is that anybody can die from a heart attack, a fall, cancer, etc. But only those that swim in oceans with white, tiger and bull sharks, are vulnerable to dying from a shark attack. As an ocean swimmer in SF, it is safe to say that the odds of dying from a shark attack are closer to 1 in 1750 than the 1 in 3.75 million_ being advertised out there. So, contrary to what the Alcatraz swimmer said, he is actually much more likely to die from a shark attack (one in a handful of thousands) than from being struck by lighting (1 in 79.000).

Notes/Sources

Note 1: In the 10 years between 2005 and 2014, 702 worldwide shark attacks, of which 31 were in CA (4.4%). 59 fatal WW attacks, of which 3 were in CA (5%). https://www.flmnh.ufl.edu/fish/sharks/statistics/Act.htm

Note 2: Between 1926 and 2014 4.3% of shark attacks in CA and 10% of fatal attacks in CA took place in SF. http://www.flmnh.ufl.edu/fish/sharks/statistics/gattack/mapca.htm

Note 3: Between 1900 and 2009, 43% of shark attacks were to swimmers and bathers. https://www.flmnh.ufl.edu/fish/sharks/statistics/Act.htm

Note 4: Assuming that there are 1750 regular ocean swimmers in SF… assuming that 80% of the 1100 Dolphin Club members and 80% of the 1100 (?) SERC members are regular swimmers

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Comments

  • dc_in_sfdc_in_sf San FranciscoCharter Member

    Do you have any records that say that there have been any shark attacks actually in SF Bay? The South End does a couple of swims that are outside the bridge but the vast majority are in the Bay.

    I strongly suspect that SF shark attacks are probably concentrated on surfers...

    http://notdrowningswimming.com - open water adventures of a very ordinary swimmer

  • mauprietomauprieto New Orleans, LAMember

    dc_in_sf said:
    Do you have any records that say that there have been any shark attacks actually in SF Bay? The South End does a couple of swims that are outside the bridge but the vast majority are in the Bay.

    I strongly suspect that SF shark attacks are probably concentrated on surfers...

    Here you can see in a map the shark attacks in the bay area in the last 100 years. The only fatal attack in the SF bay area was a swimmer killed in 1959 in Baker Beach. Inside the SF Bay, the map shows a non fatal attack in 1956 in the Municipal Pier and two attacks on swimmers before 1930 near canneries. Worldwide, according to the source in Note 3 above, 43% of shark attacks were to swimmers.

  • david_barradavid_barra NYCharter Member

    Still pretty good odds.....

    IronMikegregocMvG

    ...anything worth doing is worth overdoing.

  • Quantifying shark attack risk is tough. Shark attacks are relatively rare events, so we just don't have good statistics to do standard maximum likelihood estimates based on past events, especially for limited geographic regions. Shark populations, coastal environments, and the numbers of swimmers/surfers/etc have all changed substantially over the years, so anything that involves averages of data going back to the 20's (or even the 50's) seems questionable. This article has a decent description of recent trends off the CA cost: scientificamerican.com/article/shark-bites-are-up-but-attack-risk-is-down/

    Arriving at any specific number for the risk requires assumptions and estimates about how to count attacks and how to count the number of people (or number of hours in the water or number of miles swam). A risk of 1 in 3.7 million is probably too low, but 1 in 1750 seems too high. According to wikipedia, there were 1700 participants in the 2009 Escape from Alcatraz triathlon alone https://en.wikipedia.org/wiki/Escape_from_Alcatraz_(triathlon)

    In terms of quantifying risk, I honestly don't know how to weight 1000 people swimming 2 miles in the bay in a massive race verses, say, one person swimming 30 miles from the Farallon Islands. It would be interesting if people who study things like this for a living could include a sort of open water swimmer breakout subgroup to differentiate distance swimmers for recreational bathers, or work out ways of quantifying risk per mile or risk per hour in the water. My feeling is that you are going to end up with a small number. Not zero, but probably comparable to or less than the risk posed by hypothermia, a heart attack, or downing by some other means.

    evmophodgeszohorosemarymintNoelFigartpavlicovSpacemanspiff
  • One of the Dolphin Club members is the ED of "SharkStewards". Published a list of "how to lessen your chances of an attack".
    One comment was 'don't look like a seal".....
    Frankly, pretty useless information imho.
    Top on my list? Don't swim! But that's not going to happen..

  • gregocgregoc Charter Member

    suziedods said:
    One of the Dolphin Club members is the ED of "SharkStewards". Published a list of "how to lessen your chances of an attack".
    One comment was 'don't look like a seal".....
    Frankly, pretty useless information imho.
    Top on my list? Don't swim! But that's not going to happen..

    More to the point, stay out of the water, then you only have to worry about land sharks.

    dpm50miklcct
  • mauprietomauprieto New Orleans, LAMember

    jroyer said:

    Arriving at any specific number for the risk requires assumptions and estimates about how to count attacks and how to count the number of people (or number of hours in the water or number of miles swam). A risk of 1 in 3.7 million is probably too low, but 1 in 1750 seems too high. According to wikipedia, there were 1700 participants in the 2009 Escape from Alcatraz triathlon alone https://en.wikipedia.org/wiki/Escape_from_Alcatraz_(triathlon)

    I agree that there are tons of additional factors and variables to come up with a better quantification of risk. The point that I was trying to make was that the 1 in 3.75 million odds is not applicable because it fails to take into account the conditional probability factor. It certainly is not correct when addressing a population or an audience of surfers, divers or swimmers. My back of the envelope calculation was addressing only the conditional variable of total number of SF swimmers and number of shark attacks in SF, but it fails to take into account time tons of other variables (time in the water, # of days you swim, location, etc...). Every single swimmer has a different risk, but for sure the risk that we should have in mind is not 1 in 3.75 million. It is closer to 1 in several thousands (reminder that this is the risk over the course of 75 years, NOT the risk of dying from a shark attack every single time you get in the water).

    And just as I continue to sleep in a bed despite the odds of 1 in 8300 of dying from falling from it, I continue to swim in the bay. The odds continue to be 99.9999999999999999% in our favour that we will come out from the swim saying "I'm sure glad I swam".

    gregoc
  • evmoevmo Sydneydev

    mauprieto said:
    Every single swimmer has a different risk, but for sure the risk that we should have in mind is not 1 in 3.75 million. It is closer to 1 in several thousands (reminder that this is the risk over the course of 75 years, NOT the risk of dying from a shark attack every single time you get in the water).

    Also worth keeping in mind that the risk of death -- from anything -- over the course of a lifetime is... 100%.

    mauprietodpm50rosemarymintgregockiparizJustSwim
  • dpm50dpm50 PA, U.S.Senior Member

    gregoc said:

    More to the point, stay out of the water, then you only have to worry about land sharks.

    I never worry about this land shark. ;)

    kipariz
  • miklcctmiklcct London, United KingdomMem​ber
    edited February 2022

    How about Australia? The list is notoriously long that am I really exposing myself to risk of death by swimming in Australian water compared to the UK?

  • musclewhale89musclewhale89 Alberta, CanadaMember

    Does anyone live where there are alligators or crocodiles? I would be way more terrified of swimming in fresh water lakes where those things inhabit. I am a Canadian but lived in Florida for 6 months and saw SOOOO many alligators that there is no way I would ever get in any body of fresh water there.

  • MLambyMLamby Senior Member

    There are saltwater crocs and alligators can be in saltwater for several hours. :/:o

  • dc_in_sfdc_in_sf San FranciscoCharter Member

    @miklcct said:
    How about Australia? The list is notoriously long that am I really exposing myself to risk of death by swimming in Australian water compared to the UK?

    Australians spend a lot of time in the water that is cohabited by sharks. It is not really surprising that there are incidents. The number of attacks is pretty small when you consider the person hours involved.

    http://notdrowningswimming.com - open water adventures of a very ordinary swimmer

  • MLambyMLamby Senior Member

    Although Australia does account for around 40% of shark attacks worldwide (I believe), the one that just occurred in Sydney was the first there since the early '60s.

  • Can't give any definite numbers BUT "a significant proportion" of shark attacks here in OZ are NOT on swimmers but on divers and surfers. Some have been 1km off an island that's 20km off the mainland.

    gw

    MLamby
  • SpacemanspiffSpacemanspiff Dallas, TexasSenior Member

    @musclewhale89 said:
    Does anyone live where there are alligators or crocodiles? I would be way more terrified of swimming in fresh water lakes where those things inhabit….

    I was swimming solo in North Texas several years ago and I spotted what appeared to be an alligator about 30 meters from me. I grew up on that lake and I’ve logged perhaps 500 miles of swimming on it and I’d never seen or even considered there might be gators there. I watched it for several minutes and it didn’t move. I swam on (had no other choice) and when I got to my lunch spot, I pulled out my phone and googled “are there alligators in Lake Ray Hubbard?” Yep. And there was a person mauled/killed by one just 10 miles south of there. Yikes! I’ve researched it even more since and even reached out to the Texas Parks and Wildlife Department. They said they are typically spotted there following floods and when this happens, they issue permits and the hunters take them out in a few days, but you never know. I still swim there, but it’s a bit scarier now.

    musclewhale89MvGLakeBaggerOpenh2o

    "Lights go out and I can't be saved
    Tides that I tried to swim against
    Have brought be down upon my knees
    Oh I beg, I beg and plead..."

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