Sharks can smell blood from a long way away.

Every day, sharks are able to hunt down prey in murky and dark waters because of their remarkable sense of smell. In fact, they can detect blood from up to 3 miles away! With such a powerful sense of smell, it’s no wonder that sharks are able to hunt down prey in murky and dark waters.

But what is even more astonishing is how sharks can tell the difference between the scents of different animals and the chemicals they give off-whether it be power or fear. These olfactory abilities make them one of the most successful hunters on earth!

Answer: The time it takes a shark to get from one place to another depends on many factors, including the distance between them, swimming speed, and other factors. The answer is complicated and varies depending on the context, as with many scientific inquiries, and it differs considerably by species and environmental circumstances. However, the popular saying that “sharks can smell a drop of blood in the ocean” is entirely accurate.

The sense of smell in sharks is part of what makes them one of the most successful hunters on earth. It all starts with once airborne molecules that are able to trigger sensory hairs within a shark’s snout, which then send signals to an organ called the olfactory bulb, located at the base of the brain.

This isn’t how smell works, though. Tiny particles of whatever you’re smelling interact with chemoreceptors in your nose when you smell something—something to bear in mind the next time you encounter anything unpleasant! Before we tackle the question of how far away sharks can detect blood, let’s talk about how smell works underwater.

A shark’s nose is shaped kind of like a nostril. However, they don’t have actual nostrils or nasal passages because they lack them. The nares are similar to nostrils in that they are equipped with slightly larger openings through which the water passes when it rains. These come into direct contact with the tiny particles that a shark can smell.

Once the particles have been detected, a shark can recognize what it is. The olfactory bulb of a shark’s brain actually has thousands of tiny hair cells that help distinguish between smells. This system of detection also works for chemicals and substances along with blood.

Sharks, on the other hand, are excellent at detecting low levels of odors that imply prey—not just blood, but all sorts of organic chemicals—as far as a mile away. Even a faint odor is enough to pique a shark’s interest.

However, a 2010 research revealed that their ability to detect these odors was roughly similar to other bony fish: “This finding contradicts popular belief in the scientific literature, popular science media, and culturally. Elasmobranchs are supposed to have an exceptionally acute sense of smell, and while their sensitivity to odors at low concentrations is remarkable.

Sharks can also use their sense of smell to determine the direction that a prey’s odor is coming from. Scientists experimentally altered the source of a scent underwater in one study, and the shark was able to find it.

That’s not all, and sharks can even rely on their sense of smell to get home. And research suggests that as a result of changing ocean chemistry resulting from human-caused climate change, sharks may be losing this extremely crucial sense. We just don’t know what will happen to marine life as the ocean’s chemical composition changes dramatically owing to man-made carbon dioxide emissions.

Our oceans are already polluted with up to 150 million tons of plastic, and when our ocean waters become more acidic because of greenhouse gas emissions, sharks’ ability to detect prey could be affected!

Let’s go back to our initial question: How far away can sharks detect blood? This is a difficult issue for me to discover an accurate answer for. My shark biology and physiology texts and peer-reviewed scientific journal articles on the structure and operation of shark chemoreceptors neglect it.

This is a unique aspect of public science engagement—folks (particularly kids) ask brilliant questions that scientists didn’t consider. To obtain an answer, I eventually turned to one of my favorite children’s books from when I was younger: the Smithsonian Animal Answer Guide shark edition. It’s written for youngsters, but it’s authored by reputable experts rather than laypeople. It’s a great example of how the best scientists can explain the complicated subject matter to everyone, not just other scientists.

The distance at which they can smell something will vary considerably depending on species and ocean conditions, according to this fantastic book for young shark-o-philes that I strongly suggest (if there’s a powerful flow transporting the scent, they’ll be able to smell anything up to farther away—think about how changes in wind impact what you can smell).

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