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Sharks have long been portrayed as relentless predators, able to sniff out blood from miles away with uncanny precision. But the truth, grounded in science, is more fascinating.
Sharks possess an extraordinary combination of sensory systems—including smell, vision, hearing, and electroreception—that together make them highly efficient hunters. Yet, each sense has its limits and is used differently depending on the situation.
Smell: The Myth of the “One Drop of Blood”
While sharks do have an exceptional sense of smell, it’s not as supernatural as pop culture might suggest. According to research published by Gardiner et al. (2014) in Biological Reviews, sharks can detect certain chemical cues like amino acids in seawater at extremely low concentrations, sometimes as low as one part per billion, but claims of them smelling “one drop of blood from miles away” are largely exaggerated. This sensitivity helps them locate prey, but their effectiveness is influenced by water movement, currents, and environmental conditions, which quickly dilute chemical cues.
There is also no evidence to suggest they respond to human blood in this manner, with various evidence showing they are not only able to tell the difference between human and fish blood for example, but also able to tell the difference between different species of fish blood.
Electroreception: Sharks’ Sixth Sense
One of sharks’ most remarkable tools is their electroreception, using specialized organs called ampullae of Lorenzini. These small, jelly-filled pores around the snout allow sharks to detect the faint electrical fields emitted by all living animals. Research shows sharks can sense fields as weak as 1 nanovolt per centimeter, enabling them to detect hidden or buried prey (Kalmijn, 1982).
In plain english, this is an incredibly tiny electrical signal, about a billionth of a volt. For comparison, a typical AA battery has 1.5 volts. Sharks can detect electrical fields that are literally millions of times weaker than anything we would ever notice.
In real-world terms, it’s like being able to ‘feel’ the heartbeat of a fish hidden under sand or behind a rock, just from the tiny electric signals their muscles and nerves produce. Even if a fish is perfectly still, sharks can still sense the faint electrical ‘hum’ of its body.
This superpower helps them hunt in murky water, at night, or when prey is hiding, making them highly effective, even when other senses like sight or smell aren’t enough. Humans also emit an electrical signal, which can be sensed by sharks, however evidence suggests sharks investigate larger prey based on cues and senses other than electroreception, such as vision.
Vision: Not as Simple as It Seems
Shark vision has been long misunderstood. While many sharks have excellent eyesight, they likely see the world in shades of blue and green, since most species are color-blind (Hart et al., 2011). For more information specifically about shark vision, check out our blog Do Grey/Black Wetsuits Make You Look Like a Seal? The Truth About Shark Vision and Camouflage. This is one of the main cues sharks use with larger prey, but no, that doesn’t mean they think you are a seal just because you wear a wetsuit, but they may still be curious what you are.
Lateral Line: Feeling the Waves
Sharks also have a lateral line system, a series of fluid-filled canals along their sides that detect water movement and vibration. This system allows them to feel the thrashing of an injured fish from distances where vision and smell might fail. This also means they are attuned to investigate thrashing or splashing, including when that thrashing or splashing is a human.
Hearing: Tuning into Low Frequencies
Sharks can detect low-frequency sounds (below 1,000 Hz) from hundreds of meters away. Sounds like struggling fish or boat engines can pique their curiosity and draw them toward the source (Myrberg, 2001). Given this excellent sense of hearing, surface splashing is a particularly common way that humans can inadvertently attract the interest of sharks, especially from species which hunt large mammals from below, like adult white sharks.
More Than Just Smell
Sharks are much more than blood-sniffing machines. Their multi-sensory toolkit allows them to hunt efficiently, navigate vast oceans, and play their critical role as apex predators. Understanding these senses not only helps us appreciate sharks but can also inform smarter shark bite mitigation strategies, like using non-visual deterrents or wearing gear that reduces electrical signals or confusing silhouettes.