Gruesome Shark Feeding Video Suggests They Prefer Fish to Human Blood

Sharks appear to prefer fish blood to that of humans, according to a gruesome new experiment conducted by YouTuber Mark Rober.

Rober—a former NASA engineer who is known for his popular science videos—headed to the Bahamas to test whether sharks were more attracted to human or fish blood—an idea that was inspired by a previous experiment he ran last year.

In that experiment, Rober pumped 15 drops of human blood per minute for an hour into the sea near several sharks.

"In the end, [the sharks] just weren't really that interested," the YouTuber said in his latest video. "So this busted the myths of the movies that sharks are these ruthless killers that just go crazy if they smell a drop of your blood."

The first challenge of the latest experiment involved getting hold of a large volume of fish blood. Rober and his marine biologist collaborator, Luke Tipple, solved this problem by blending around 20 dead fish into what the YouTuber described as "five gallons of mouthwatering fish blood smoothie."

"We already know that sharks don't necessarily go nuts in the presence of a little bit of human blood," Rober said. "But would they go nuts in the presence of a little bit of fish blood?"

Rober and Tipple's experiment involved towing three modified surfboards out into Bahamian waters. One board had a five gallon bucket of the fish blood smoothie attached to it, while another had a five gallon bucket of cow's blood.

Rober said they had to use cow's blood because it is hard to legally procure five gallons of human blood for these purposes.

"After talking with a couple shark scientists, they've shown experimentally that all mammal blood essentially smells the same to sharks so it wouldn't affect the results to use cow blood in place of human blood," Rober said.

The third surfboard had a five gallon bucket of seawater attached to it as a control to make sure the sharks were not just interested in the surfboards.

The team then pumped out the contents of each of the buckets into the sea over the course of an hour in order to observe how many sharks approached each board.

"One of the limitations to last year's test was that the boards might have been too close to the boat," Rober said.

"So it's possible some of the sharks actually smelled the blood but didn't investigate it because they were just waiting for a handout from the boat. So this time, we basically placed the boards in the middle of the frickin' ocean, super far away from the boat so it wouldn't be a confounding variable."

After the pumps were activated on the buckets, Rober and Tipple sent out a camera-equipped drone to observe any shark activity around the surfboards.

"Things were pretty quiet for about the first 20 minutes but then we had our first hit on the mammal blood board. But pretty soon thereafter, things started heating up for the fish blood smoothie board," Rober said.

reef shark
Stock image: A reef shark swimming near the sea bed in a tropical ocean. iStock

After an hour, the the team tallied up the results from the drone footage, finding that the sharks appeared to be significantly more attracted to the fish blood surfboard than the other two.

In total, the mammal blood board was approached eight times while no sharks approached the seawater control board. The fish blood board, on the other hand, was approached 134 times, according to Rober, strongly suggesting that the sharks had a preference for the fish blood.

"The main takeaway for me from this experience is that sharks have been on this planet longer than the dinosaurs, or even trees have. So they've had 400 million years of evolution to develop these instincts that are rewarded for smelling fish blood. Humans and cows will be an extremely rare delicacy so it makes sense that it's just not hardwired into their brains."