Sharks have six highly refined senses for both hunting and communication: vision, taste, smell, hearing, touch and electro-reception. These finely honed senses coupled with sleek, torpedo-shaped bodies make most sharks highly skilled hunters.
The structure of shark eyes is remarkably similarly to our own. Like ours, the pupils of many shark species change size in response to varying levels of light. They have rods, which sense light and darkness, and most have cones, which allow them to see color and details. (Some sharks have no or few cones, making them colorblind.) Like a human eye, a shark eye has a cornea, lens, pupil and iris. Unlike us and more like cats, sharks have a layer of mirrored crystals behind their retinas called the tapetum lucidum. This layer allows them to see better in dark and cloudy waters, in the deep sea or at night.
But within that basic plan, there is a wide range of seeing ability among shark species. Some have large eyes, such as the bigeye thresher shark (Alopias superciliosus), with eyes six centimeters in diameter. Other sharks have very small ones, like the one-centimeter diameter eyes of the brownbanded bamboo shark (Chiloscyllium punctatum).
A 2007 study found that shark eye size varied depending on the shark’s habitat. Many sharks that stay near the surface have evolved to hunt in the sunlight and rely on their vision more than other senses, so have large eyes. Some deep-sea sharks also have big eyes to pick up faint traces of light down in the darkness—but their eyes are loaded with light-sensing rods and have fewer color-sensing cones. Researchers also have found that bioluminescent deep-sea sharks have a higher density of rods in their eyes than their non-bioluminescent counterparts, allowing them to see more details in the dark water when bioluminescence is present. Sharks that live in shallow water on the seafloor often have the smallest eyes because floating sediment kicked up from the bottom blocks their vision. These animals instead rely on senses like smell and electroreception over vision. Lastly, sharks that hunt fast-moving prey like fish and squids have bigger eyes (and presumably better eyesight) than those that eat non-moving prey.
Sharks have eyelids, but they don’t blink; they close their eyelids to protect their eyes from damage when fighting or feeding. But their eyelids don’t close all the way. In addition, some species have a clear membrane (the nictitating membrane), which slides down to protect the eye in dicey situations. Shark species that don’t have the membrane, like the great white shark, will roll their eyes back in the socket when they are attacking prey for protection.
Sharks don’t have a very strong sense of taste. Taste buds that line the mouth and throat allow them to taste their food before they make the commitment to swallow. This helps them avoid dangerous prey items, which might have a bad taste. This could also be why many shark bite victims survive: the shark takes a bite, gets a bad taste in its mouth, and decides it doesn’t want to eat, releasing the person.
Sharks don’t have what we think of as a typical tongue. Instead they have a small piece of cartilage on the floor of their mouth called a basihyal that lacks taste buds. In most sharks, it doesn’t appear to serve any real function. But the cookie-cutter shark (Isistius brasiliensis) uses its basihyal to rip small chunks of flesh from fish and other animals.
Sharks have truly remarkable noses. As they swim, water passes into their nostrils and across sensory cells lining the skin inside. These sensory cells are able to detect relatively small amounts of a chemical signal in the water. A shark’s two nostrils can also detect smells separately to determine from which direction they originated, allowing them to smell in stereo. Just like we can tell where a sound is coming from depending on which ear the sound waves hit first, sharks can tell where a smell is coming from depending on which nostril the smell hits first. Now those are some impressive nostrils!
Sharks have two small openings on their head (behind and above their eyes) that lead to internal ears. There, sensitive cells allow sharks to hear low frequency sounds and to pick up on possible prey swimming and splashing in their range.
Sharks don’t have fingers that they can use to feel and touch. Instead, like other fish, a shark has a lateral line running along the middle of its body from head to tail. The lateral line system is a series of pores that lets water flow through the shark’s skin, where special cells called neuromasts can detect vibrations in the water. A fish swimming nearby displaces water as it goes along, creating ripples; when those ripples hit the lateral line system, the shark can detect both the direction and amount of movement made by prey, even from as far as 820 feet (250 meters) away. Because of this ability, they can sense prey in total darkness.
Not only can sharks detect vibrations through their lateral line system, but they also have a “sixth sense” of sorts that allows them to detect the small electric fields that all animals create when their muscles contract. Sharks detect the electrical fields through small pores on their head that are full of special cells called ampullae of Lorenzini. These cells are filled with a jelly-substance that conduct electric charges received from ions, like sodium and chlorine, which are found in salt water. When a fish moves its muscle to swim, the shark can feel it; when one is wounded and flopping around, it sends out a large electrical signal that will attract the shark.
Sharks also use electroreception to navigate. They can sense the Earth’s electromagnetic field, which likely allows them to migrate across large distances without getting lost. They can also sense objects in the water, allowing them to create a map of their immediate environment.