Sharks have an amazing arsenal of senses that have been evolving over the last 450 million years. Their highly developed senses include
- Audio Reception
- And Taste
These 7 senses are uniquely honed in each species for their particular life histories, behaviors, and environment. While each species may have their own adaptations, there are some sense characteristics that define the shark superorder of Selachimorpha (Skomal, 2016; Parker, 2008).
We’ve all heard that sharks can smell a single drop of blood of an Olympic sized swimming pool- or some variation of that! That’s because smell is the most powerful sense that sharks posses (Skomal, 2016). In fact, the majority of the shark’s brain has developed to process olfactory sensations (Parker, 2008). Despite this keen development, sharks are only capable of sensing a limited range of substances, specifically those related to prey (i.e. bodily fluids and blood), predators, and even potential mates (i.e. pheromones) (Skomal, 2016; Parker, 2008). Studies have shown that sharks are most responsive to bodily fluids and the secretions of an injured or distressed animal (Parker, 2008).
Unlike terrestrial animals, the olfactory system of sharks is not connected to their respiratory system. The nostrils, or nares, are external and provide the flow of seawater to and from the olfactory organs (Skomal, 2016). The nares are divided by a flap of skin into incoming and outgoing water flow. The water flows into the nare over a series of plates which contain odor receiving receptors. From the receptor, the odor is then communicated to the olfactory bulb of the brain (above photo) (Skomal, 2016). Once a scent is detected, the shark will swing its head back and forth to determine the strength and direction of the smell (Parker, 2008). When a scent is detected in one nare stronger than another, the shark turns in that direction until the scent is directed more strongly in the opposite nare. The shark then turns back across the scent trail, thus swimming in a zig-zag pattern across the scent trail until it is within range of its other extraordinary senses (Parker, 2008).
Sharks do not make any sounds of their own – despite what Hollywood film makers seem to believe! (As though Hollywood gets everything else right about sharks!
FilmToaster (2016, June 20). Jaws the Revenger (1987) | AMC Uncut Ending in Blu-ray HD [Video Clip]. Retrieved from https://www.youtube.com/
Sharks are capable of hearing sounds from great distances. Sound waves are conducted much more efficiently in water than air. This means they are able to travel further under water than in air (Skomal, 2016). Sharks do not have external ears, however they have an inner ear that is involved in balance and sound perception- much like our own inner ear (Parker, 2008; Skomal, 2016). While it is unclear the exact range of sounds sharks are capable of hearing, both in frequency and in volume, a number of shark species have expressed wonderful hearing capabilities (Parker, 2008). For example, the bull shark (Carcharhinus leucas) react to sounds ranging in frequency from 20 Hz to 1,000 Hz. For us, that would range from hearing the deep boom of thunder to the high notes of the human voice (Parker, 2008). Whale sharks (Rhincodon typus) have the largest inner ear structures known in the animal kingdom (Martin, 2007). While the hearing capabilities of the whale shark has not been studied, it has been suggested that such large hearing structures would be sensitive to long wavelength, low frequency sounds, such as an inboard motor of a boat (Myrberg, 2001). Whale sharks have often been observed diving in suspected response to the ignition of a nearby inboard motor (Martin, 2007).
Shark vision is incredibly interesting – or at least I think so, but then I worked in retinal ophthalmology for 7 years! Shark eyes are located on the sides of their heads, providing them with a nearly 360 degree field of vision, however there is no overlap in their view (Skomal, 2016; Parker, 2008). This lack in overlapping fields of vision means that sharks are unable to judge distances well by binocular or stereoscopic vision alone (Parker, 2008). Sharks must rely on their other senses to help judge distances and hone in at close range. The anatomy of their eyes are similar to other bony fishes, with a few unique adaptations. They have a dynamic iris, large lenses with UV filtering properties, and a reflective layer called the “tapetum lucidum” (Skomal, 2016). The tapetum functions like a mirror behind the retina, reflecting light back into the retina to increase sensitivity. Cats have this layer as well, it’s what causes their eyes to glow green in the dark when a light is shown on them. For years it has been debated the extent to which sharks can perceive color. The lining of the shark retina does contain both rods and cones. However, the retina contains millions more rod cells which do not perceive color, compared to the cones cells which do. It is suspected that sharks possess both rods and cones not to necessarily perceive color, but to efficiently hunt in low light conditions, such as ambushing prey at sunrise or sunset, prime hunting times for the majority of shark species (Skomal, 2016).
All fishes have a specialized sensory system that allows them to detect movements within the water called the lateral line (Skomal, 2016). The lateral line is often also referred to as mechanosense. These sensory receptors are located in the shark’s skin extending from the shark’s snout bi-laterally to the caudal fin in shallow pits and grooves. The mechanoreceptors within the pits are neuromasts comprised of sensory hair cells covered in gelatinous cupula (Skomal, 2016). These mechanoreceptors allow the shark to detect water displacement, current movements, avoid predators, and detect prey. It can even aid the shark in physical interactions with other sharks, such as schooling, and avoiding obstacles (Skomal, 2016).
The ampullae of Lorenzini were first described by Stefano Lorenzini, an Italian physician and ichthyologist, in 1678. These small gel-filled chambers are complete with sensory cells and a tube-like canal from the surface into the skin. These sophisticated sensory organs enable sharks to detect low frequency electrical fields created by living organisms. Sharks are able to detect electrical fields as low as one billionth of a volt! To put that into perspective, that is the equivalent of sensing a few small batteries spread thousands of miles apart (Skomal, 2016)! Despite this incredible ability, sharks use this electrosense at close distances, typically within just a few feet to locate prey (Skomal, 2016; Parker, 2008). Actively hunting species, such as the bull (Carcharhinus leucas) or hammerhead sharks (Sphyrnidae), can have 1,500 or more ampullae located in their snouts and across their heads. While sluggish bottom dwelling species that do not actively hunt may only have a few hundred ampullae (Parker, 2008). Sharks are even able to detect the Earth’s magnetic fields and use these fields to navigate during migration (Skomal, 2016).
While shark skin is typically very tough, sharks can feel a certain amount of basic contact and can receive information such as temperature, chemicals, or physical damage (Parker, 2008). These changes are detected by bare endings of the sensory nerves called “free nerve endings” which are embedded in the skin (Parker, 2008). Sharks also use touch to explore an unfamiliar item in their environment. Often sharks will bump an object with their snouts to gather information and help determine whether a new item is a prey item (Skomal, 2016).
Martin Levy (2016, May 11). Shark Bump [Video Clip]. Retrieved from https://www.youtube.com/
While it is documented that sharks have taste buds- scientists have even mapped the taste buds of a few species- it is not well known whether sharks are able to discriminate between bitter, sweet, salty, or sour (Skomal, 2016). However, limited research suggests that sharks use taste to determine whether or not an item is food. This means they use their mouths and teeth to gently explore an item before consuming it. If an item isn’t up to their standard, it is spat back out almost instantly.
The Senses Come Together
See how all the senses come together for a hunting shark!
cx Sharks (2016 May 25). CORSGBBC2016-V002700 [Video Clip]. Retrieved from https://www.youtube.com/
Thanks for reading! The new Ocean For Sharks Shop is open! There’s handmade ocean inspired plush animals, canvas paintings, and of course my children’s book, Winifred the Wondrous Whale Shark, available in print and PDF. Be sure to stop by. Remember proceeds benefit shark research and conservation with a donation to Project AWARE!
Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time finatics!
Featured Image Source
Morris Brake, J. (Photographer). (2016). A great hammerhead cruising over sand in Bimini [Digital Image]. Retrieved from http://www.divephotoguide.com/
Martin, R. A. (2007). A review of behavioural ecology of whale sharks (Rhincodon typus). Fisheries Research, 84(1), 10-16.
Myrberg Jr, A. A. (2001). The acoustical biology of elasmobranchs. In The behavior and sensory biology of elasmobranch fishes: an anthology in memory of Donald Richard Nelson (pp. 31-46). Springer Netherlands.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.
Tricas, T. C., Deacon, K., Last, P., McCosker, J. E., Walker, T. I., & Taylor, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.