Sharks: can the ocean predators smell blood in the water?

Former NASA engineer and YouTube star Mark Rober decided to travel to the Bahamas to put an old theory/myth to the test.

Do sharks really smell a drop of blood from a mile away?

To complete the test procedure, the YouTuber put himself in the middle of the ocean on a boat surrounded by sharks.

He also sat down with marine biologist and shark diving specialist Luke Tipple to help set up the experiment.

The goal was to test how far sharks could smell a single drop of blood in the water. But before that, Rober needed to know that they actually preferred blood over any other scent.

Fish Oil, Cow's Blood, Sea Water, and Urine

So, Rober placed four surfboards equidistant from the back of the boat in the crystal clear waters of the Bahamas.

Each board hosted two liters of a different liquid, which were pumped into the ocean for an hour, and then counted how many sharks went over to check them out.

The bottles contained fish oil, cow's blood, seawater, and urine.

The surfboards were anchored, and the experiment began. After 20 minutes, there wasn't a lot of action around the boards, especially at the fish oil, urine, and seawater (control) boards.

Mark Rober's shark test: he used surfboards as platforms for dropping fish oil, cow's blood, seawater, and urine into the water | Photo: Rober/Archive

The blood board started attracting some smaller fish, and soon, one or two sharks began taking notice.

With 15 minutes on the clock, the blood line attracted a line of sharks, which were swimming up the enticing red trail. But when they reached the board, they lost interest.

The results were interesting.

The urine and seawater boards attracted zero sharks, the fish oil board attracted four sharks, and the cow's blood board attracted 41 sharks.

The Human Blood Test

But one question remained: would sharks have a taste for fresh human blood?

Three boards were placed in the water.

The control board was put in the middle. Then, another board was going to release a drop of human blood per minute, and the third one was about to pump blood fast at an average of one drop every four seconds.

Again, there wasn't much action in the early minutes of the experiment and, in the end, researchers concluded that zero sharks had checked out all three boards.

"I think it's safe to qualitatively say that if no sharks came to check out 15 drops of human blood a minute in the middle of shark-infested waters, you're probably going to be okay with a small scrape," Rober concluded.

"There certainly won't be some kind of feeding frenzy with a single drop of blood from all sharks within a mile."

However, it is important to stress that these experiments did not involve all types of sharks and that there were no humans - like surfers sitting on their surfboards - in the water.

So, precaution is mandatory when swimming and surfing in shark-infested waters.

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