Mark Rober Finds Out If Sharks Can Really Smell a Drop of Blood From a Distance

Shark Week — everyone’s favorite marathon of predator-centric entertainment — has just kicked off, and that means that everyone is breaking out all of their favorite shark “facts” around the water cooler. Some of those are true, and others are quite false. Sharks do, for example, feed on your fear. But they won’t follow your family to other countries to seek revenge. Another fact that you’ve almost certainly heard is that sharks can smell a single drop of blood from more than a mile away. To find out if that’s true, Mark Rober took a trip to the Bahamas to test it out.

Along with that, Rober also wanted to find out if sharks were attracted to other substances. That calls for a scientific experiment with controls, so Rober set up four surfboards: one to dispense cow’s blood, one with human urine, one with fish oil, and one with local seawater as the control. Each surfboard was equipped with a peristaltic pump to drop its liquid into the water without contaminating it. Those pumps are controlled by an Adafruit Feather M0 RadioFruit board through an Adafruit Motor FeatherWing.

It was important for the experiment that each board started pumping at the same time, which is why the RadioFruit boards were used. Rober could send a single radio signal that would start all of the pumps simultaneously. They then just had to observe which substance attracted the most sharks. Unsurprisingly, it was the cow’s blood. Fish oil also attracted a couple, but the urine and seawater were ignored completely.

That does, however, still leave the question of how much blood it takes and how close the shark needs to be to it. To test that, they conducted another experiment. This one used two surfboards with human blood, and one with seawater as a control. One of the surfboards pumped blood quickly, and the other pumped slowly. In that test, they found that the sharks weren’t interested in either, despite the blood being within a hundred yards of them. The conclusion is that sharks either can’t detect small amounts of blood far away, or that they simply don’t care about it.