What are your real chances of getting bitten by a shark?

I was in Maui yesterday and I was thinking about going for an open water swim with a local club. The swim kicked off from Makena beach.

But then, I started thinking about sharks.

Everyone hears stats on how unlikely it is to be bitten by a shark. You only have a ~1 in 4 million chance of dying right? Right!?

But when you are about to go swimming in an area known to have lots of tiger sharks (on any given day, there’s an 80% chance a tiger shark will be spotted at Makena point), you start to get REALLY curious on how all those stats get calculated.

It turns out, the 1 in 4 million number is just taking the total number of shark fatalities over the population of the U.S. Why are they counting a farmer in Arkansas that has never set foot in shark infested waters in the denominator?

We can do a better. Let’s try to calculate a better stat for Maui.

There are around 167k residents of Maui and around 58k daily visitors. I’ll assume 10% of residents go in the water on any given day. But wading 5 feet offshore isn’t a real risk. The vast, vast majority of shark attacks happen 25+ yards offshore. So let’s assume ~3% of locals venture out 25+ yards and when they do, they spend an average of 2 hours there (swimming, surfing, snorkeling, etc.).

For visitors, I assumed 66% ventured into the water and 2% went 25+ yards out with the same 2 hour window.

So in total, 1,273 people enter deep water on any given day and spend 2,547 hours there.

Now, in the last 10 years, there are 33 recorded shark attacks in Maui, so on average, there are 3.3 per year. Said differently, that’s 0.009 shark attacks per hour. Let’s divide that by the number of swim hours per day (2,547) to get the risk per hour.

So my estimate of your chance of getting attacked by shark when you’re 25+ yards offshore for 1 hour in Maui is 0.0000036. Around 12% of shark attacks were fatal in the last 10 years in Maui, so there’s 0.0000004 chance of dying from a shark attack per swim hour.

That number by itself is hard to grasp. It’s a lot of zeros. We need something to compare it to. So let’s compare to something common — like driving.

There are 1.2 car accident deaths per 100,000,000 miles and 0.7% of car accidents are fatal. So in other words, there are 0.0000017 car accidents per mile travelled. We’ll assume the average driver goes 40 mph so that brings the aggregated risk to 0.000069 accidents (and 0.00000048 deaths) per hour of driving.

So how do share attacks compare to driving?

The Takeaway

1. The chances of getting attacked by a shark in Maui while you’re 25+ yards offshore for 1 hour is 1/20 the chance of getting in car accident if you drive for 1 hour. You hopefully are not getting in many car accidents, so it’s encouraging the chances of a shark attack is 5% of that.
2. However, when they do occur, shark attacks are much more fatal than car accidents. As such, the chances of dying from a car accident when you drive for 1 hour is roughly equal to swimming 25+ yards offshore in Maui for 1 hour and getting killed by a shark.

Again, these are my best guesses and I tried to be transparent with my assumptions.

Unfortunately, I didn’t have time to do these calculations prior to the open water swim and I missed it. If I had know these risk stats, I would’ve definitely done it! It’s a level of risk I can stomach.