Just as humans have evolved advanced senses over time, carefully fine-tuning them for ever-varying environments, so too have sharks (and all other plants + animals on the planet for that matter)!
Sharks have a full arsenal of unique senses that help them survive their watery world. In this post, we're diving into each sense to learn about how they've helped sharks survive millions of years.
The first five of these senses you may recognize as humans and animals utilize many of the same senses to navigate the world. How we find food, how we can detect danger, even how to communicate with a loved one.
1: HEARING
Interestingly, sound is the first sign that a shark's prey item is close by - think splashing or the thrashing of an injured fish.
Sharks hear sounds with frequencies ranging from 10 hertz to 800 hertz, easily detecting prey at distances of more than 800 feet (two football fields)! In comparision, humans hear sounds ranging from 25 hertz to 16,000 hertz.
Sharks have an inner ear made up of three semicircular canals, with each canal containing sensory maculae. These sensory areas, lined with tiny hairs, are responsible for both balance and sound perception as well as help a shark detect any vibration in the water column.
2: SMELL
Sharks use scent to detect prey, decipher danger from an incoming predator, or even find a mate. There are many amazing studies around the sharks' sense of smell - you may have caught some of them in action on Shark Week. It's an amazing ability and evolutionary feat that sharks can detect one part of blood per one million parts of water. (Equal to one teaspoon in an average sized swimming pool)
DID YOU KNOW:
Up to two thirds of the total weight of a shark's brain
is dedicated to smell- understandable as it is such a vital
sense for their survival in the ocean!
3: VISION
Just like the human eye, a shark's eye includes a cornea, iris, lens and retina; they also have rods and cones which allow a shark to see in color and at differing levels of light.
Also like humans, sharks must protect their eyes. Depending on the species, a shark may have a nictitating membrane (think eye lid), while others, like great whites, roll their eyes back into the sockets.
Most shark’s see their prey at about 70 to 100 feet away! Shark eyes are 10x more sensitive to light than ours and similar to cats, sharks also have a mirror-like layer in the back of the eye called the tapetum lucidum, that enhances the eye’s sensitivity to light.
4: TOUCH
Sharks may not have hands to feel as humans do, but that doesn't mean they don't have nerve endings under their skin. Sharks also experience distant touch through their lateral line.
Additionally, some species (Wobbegong and Angel sharks) have barbells around their mouth that can be used to probe the sand for prey or aid to camouflage them helping attract prey into ambush range.
Shark's teeth also have many pressure sensitive nerves. Living in a habitat as vast as the ocean sharks must be opportunistic and may rely on 'test biting' to determine if an object is prey.
5: TASTE
Sharks do not have nor use tongues like humans or other mammals do. In fact, sharks have what is called a “basihyal” that they use for feeding and swallowing, and not for tasting things in the same way mammals do.
While the sense of taste in sharks may not seem as highly developed as other senses, it is believed their receptors help them distinguish if something is or is not food (like human sense of taste help identify if food is edible). For now, there is no evidence that sharks can distinguish between bitter, salty, sour or sweet.
DID YOU KNOW:
Sharks often ‘test bite’ potential food to see if it's palatable. If it's not they'll spit it out, unless your talking Tiger sharks - the garbage disposals of the sea, know to eat anything from floating fruits or even objects made of metal!
The next senses play a vital role in how the shark navigates their watery realm.
*Depending how shark scientist break them up, some may group their electro-sensory related senses together, saying there are 7 main senses; for the purpose of explanation we are separating Lateral Line, Pit Organs, and Lorenzini.
DID YOU KNOW:
The lateral line, pit organs and their Lorenzini senses have only been discovered and/or researched in the last 10-20 years! Just think of how many more functions we don't yet fully understand.
6: LATERAL LINE
A shark's lateral line, comprised of neuromasts, runs down the side of a shark (or fish) and allows them to sense pressure as well as any vibration changes in their environment. A shark's own body movement creates waves that bounce off obstacles (like reefs), and helps them create a 'pressure map' of their surroundings.
Research suggests that the lateral line aids a shark in obstacle avoidance, their orientation and currents, as well as feeding behaviors in regard to tracking prey and hunting success.
7: PIT ORGANS
Elasmobranchs have hundreds of tiny sensory organs, called pit organs, scattered over their skin. Electron micrographs have now revealed that the pit organs are indeed free neuromasts that contain sensory hair cells.
The behavioral role of pit organs remains mysterious, some suggested that they may play a role in prey capture under dim light conditions. While other researchers suggest that pit organs function as detectors of swimming speed.
8: AMPULLAE OF LORENZINI
In 1678, Stefano Lorenzini (an Italian anatomist) noted something interesting about the the pores in which concentrated around sharks' mouth. Lorenzini found that if he peeled back the neighboring skin, each opening led to a long transparent tube that was filled with a crystalline gel.
It wasn't until the 19th century with an improved microscope that it was revealed the pores on a shark’s snout and the unusual structures underneath them, today called ampullae of Lorenzini, must be sensory organs of some kind.
The tiny pores along their bodies are extremely sensitive and can detect even the faintest of electrical field - Such as those generated by the Earth’s geomagnetic field or muscle contractions in prey.
Today, we understand that sharks have a very complex electro-sensory system to increase their predatory success. Using these senses, sharks are able to hunt otherwise unseen prey items like rays or crustaceans hiding under the sand.
"Sharks use all their senses when they hunt, but each one has special advantages and different sensitivities. Smell and hearing would be most useful for locating prey from great distances. Vision, lateral line senses and taste would become more important at closer ranges."
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