Can Sharks Smell a Drop of Blood Miles Away?

Sharks possess an incredible sense of smell. They use this ability to find food, mates, and safe areas in the vast ocean. While the idea that a shark can smell a single drop of blood from miles away is a popular myth, the truth is still impressive. Most sharks can detect blood at one part per million. This is roughly the same as putting one drop of blood into a large backyard swimming pool.

How Sharks Smell

Unlike humans, sharks do not use their noses to breathe. They have two openings under their snouts called nares (nostrils). As the shark swims, water flows into the nares and over sensitive skin folds inside. These folds contain special cells that detect chemicals in the water.

The information travels immediately to the brain. In some sharks, the olfactory bulb (the part of the brain that handles smell) takes up two-thirds of the total brain weight. This allows them to identify very faint chemical signals in the water.

Tracking the Source

A shark cannot smell something instantly if it is far away. The scent must travel physically through the water to reach the shark. Ocean currents carry smells just like the wind carries smoke. If the current is moving quickly, the smell travels faster. If the water is still, the scent takes longer to spread.

Once a shark detects a scent, it swims toward the source. It compares the strength of the smell entering its left nostril versus its right nostril. If the smell is stronger on the left, the shark turns left. This causes the shark to swim in a zigzag pattern as it follows the invisible trail through the water currents.

Combining Senses

Smell is often the first sense a shark uses to find prey from a distance. As it gets closer, it uses hearing and sight. Finally, at close range, it uses special pores on its snout called ampullae of Lorenzini. These pores detect the tiny electrical signals made by the heartbeat and muscle movements of other animals.