Do Sharks really smell blood?
Carley Lerner/ Reader’s Digest
While the extent of their smelling abilities is often exaggerated, sharks can smell blood in the ocean. Maddalena Bearzi, marine biologist and President of the LA-based nonprofit Ocean Conservation Society, told Reader’s Digest that most sharks “have a keen sense of smell, which is used—among other things—in detecting dead or wounded prey.” Wondering how these animals smell underwater? “The nostrils of sharks have specialized, sensitive cells located on the underside of the snout and these cells are used exclusively for smelling,” says Bearzi. “When water flows through the nostrils of a shark, the chemicals react with the receptors in these sensory cells, sending signals to the brain. Thanks to these sensitive cells and an enlarged olfactory bulb, these animals can detect even tiny amounts of specific chemicals present in the water,” Bearzi explains. For less biologically minded people, this means that sharks do have a strong sense of smell, can detect small amounts of chemicals (including blood) in the water, and often rely on their sniffing powers to hunt prey. This does not mean that sharks can smell blood everywhere in the ocean. Most people believe that sharks can smell a drop of blood in the ocean from a mile away. This is thanks to “shark attack” movies, which dramatically portray the animals crossing great distances to follow the scent of a splash of human blood. In reality, however, one of the fascinating and reassuring facts about sharks is that “sharks can’t smell blood across an ocean with a sort of ‘supernatural’ sense,” clarifies Bearzi. While all species of sharks are different, some “can detect smells at about one part per 10 billion, depending on the chemical,” Bearzi explains. For context, one part per 10 billion is “basically about one drop of blood in a swimming pool,” the marine biologist explains. This means that, if there were only a single drop of blood spilled in the ocean, the shark would have to be within relatively close proximity to be able to smell it. At the same time, when sharks do come into contact with a smell, they “are extremely good at picking up on the smallest molecules to direct them to prey sources,” says Mike Price, Curator at SeaWorld San Diego. On land, when “something is concentrated enough that humans can smell it miles away” it is usually because the wind carries molecules of the smell across distances, says Price. Similarly, in the sea, “as a ‘smell’ dilutes across ocean currents, sharks only need to bump into one or two molecules of a particular prey and they are able to track that prey source down over long distances,” says Price. So, while sharks can’t smell blood from extremely far away, they are very good at finding the source of the blood after coming in contact with the scent.