Smell is undoubtedly the most important sense for sharks, to the point where they’ve been dubbed “swimming noses”. Some impressive numbers back this up. A shark can detect fish extracts that make up one part of ten billion. According to other research, sharks can respond to one part blood per one million parts water, which is equivalent to being able to smell one teaspoon of something in a pool. Furthermore, sharks can detect minuscule concentrations of these substances from hundreds of meters away.
What is the shark’s method for accomplishing this? Two nares, or nasal cavities, are located just beneath the snout. There are two holes in each nare: one for water to enter and one for water to depart. To sniff out any signs of prey, the shark sucks or drags water into its nares. Water enters nasal sacs and passes through a series of skin folds called olfactory lamellae. Because the shark’s nasal canals are large, it has more time to register odours. Sensory cells fill the nasal sacs, which convey messages to the shark’s brain. The olfactory lobes of the shark’s brain assess odours, looking for scents that match its prey’s or potential mate’s pheromones. Sharks have quite a complex machinery up there, too: olfactory lobes make up roughly two-thirds of the shark’s brain weight.
When a shark detects a scent and decides to pursue it, it begins swimming. The shark’s normal swimming motion, which involves moving its head back and forth, aids in locating the source of the scent. The nose gathers up more water for the shark to evaluate with each movement, and the shark can distinguish whether it’s coming from the right or left nare. This aids them in determining which direction to swim in.
Because it doesn’t have to do anything else, the shark’s nose may perform so well. Sharks only use their nostrils to sniff. Sharks breathe through their gills, and their sense of smell is not connected to their mouth in any manner. Sharks don’t always know how something will taste until they bite into it. This is how some individuals can “escape” a shark attack: the shark takes a small bite of the prey’s foot and decides to reject it.