Can sharks smell a drop of human blood in the ocean?

sharks lined up following blood in the current.

If you know anything about sharks, you have probably heard that their super sensitive snouts can sniff out a single drop of blood in millions of gallons of water. Mark Rober, a former NASA engineer, teamed up with Discovery Channel for a Shark Week blood test.

Rober set out to test the theory that sharks are attracted to a drop of human blood in the ocean.

With his friend Sean Hodgins, Rober created four receiver boxes with custom made shark blood circuit boards. The boards were radio controlled and connected to a peristaltic pump. The pumps were connected to IV drip-type bags which each contained different fluids.

When Rober, who worked with NASA on the Curiosity Rover for 7 years, arrived in the waters off the Bahamas he was met by marine biologist Luke Tipple. The two discussed their plan to connect the custom devices to surfboards and float them away from the boat, which was already surrounded by sharks.

The first test was to determine if sharks preferred the smell of blood to other human scents.

The crew pushed four surf boards out around 50 yards from the back of the boat. One set up had cows’ blood, the second human urine, the third fish oil and the fourth was a control using sea water.

After the boards were placed a drone was flown over the test area as two liters of each liquid was slowly released. After an hour the footage was reviewed and each time a shark came within 3m (9.8ft) of the board, it was counted.

The results showed zero sharks investigated the urine and sea water boards, four looked at the fish oil board and 41 sharks were drawn to the cow’s blood board. The footage also showed several sharks followed the blood as it flowed in the current and traced it to the source.

A second test was performed with fresh human blood pumping slowly on one board, pumping fast on another, while a third control pumped sea water. The results had zero shark interactions on any board.

Does this prove that sharks are attracted to cow’s blood and not human blood? Not really, but it is interesting experiment.

The main issue is the location. When Rober arrived at the location, the boat was already surrounded by sharks and could be a baited shark dive location. Sharks have been known to congregate around boats in some locations and may associate boats with food.

Sharks do have a great sense of smell, but it depends on the species of sharks as to how far away and how much they can detect.

According to the American Museum of Natural History, lemon sharks can detect the equivalent of 10 drops of fish oil in an average-sized home swimming pool. Other sharks can sense one drop of fish oil in an Olympic-sized pool.

So is it safe to swim with an open wound? It’s not advisable.

Sharks are curious, and if blood is present in the water, it could attract an unwanted visitor. In addition, recently there have been cases where beach goers have contacted flesh eating bacteria, particularly shoreline areas off the Gulf of Mexico.

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