Sharks have captivated humans for centuries with their stealthy hunting abilities and intimidating appearance. One of the most striking features about sharks are their eyes, which allow them to expertly track prey even in murky waters.
If you’re wondering what color sharks’ eyes are, you’ve come to the right place.
In short, most sharks have black eyes, though some species may have green, blue, yellow, brown, or grey eyes depending on their environment and diet. Now let’s dive into the details…
An Overview of Shark Eyes
Sharks have incredibly complex eyes that aid their hunting abilities in various marine environments. Their eyes possess special adaptations like the tapetum lucidum that enhances vision in dark or murky waters.
There are also noticeable differences between shark species in terms of eye placement, size, color and structure.
Shark Eyes Aid Their Hunting
A shark’s eyes are perfectly adapted for locating prey in the ocean. They are placed on either side of their head to provide a panoramic view of their surroundings. This gives them excellent peripheral vision to detect movement and potential threats.
Their eyes also have a flattened cornea which allows them to see clearly both above and below the water. Some species like the great white even have receptors that detect small electromagnetic fields emitted by prey.
Sharks can also retract their eyes into sockets for protection. When hunting, they will protrude their eyes to improve visibility. Certain species like bull sharks and tiger sharks have eyes towards the front of their head for better binocular vision to accurately attack prey.
Tapetum Lucidum Enhances Vision
One of the most incredible shark eye adaptations is the tapetum lucidum. This is a reflective layer behind the retina that acts like a mirror to double the amount of light passing through the eye. It allows sharks to see clearly even in very dim lighting up to 100 times better than humans!
This tapetum lucidum is what causes the eyeshine effect of sharks when light reflects back out through the retina. Deep sea sharks have the most advanced tapetum lucidum as they hunt in extremely deep and dark waters. Without it, they wouldn’t be able to navigate or find food effectively.
Differences Between Shark Species
While all sharks have excellent vision, there are some variations in eye anatomy and capabilities between species:
- Hammerhead sharks have eyes on projections from their elongated head for 360-degree vision.
- Thresher sharks have large eyes to hunt for small fish in dim depths.
- Mako sharks have eyes positioned for accurate binocular vision and estimating distances when attacking fast-moving prey.
- Tiger sharks have eyes more frontally placed than other requiem sharks for improved binocular vision.
- Nurse sharks have small eyes as they rely more on their electroreception ability than sight.
In general, pelagic sharks that swim in open water have larger eyes than bottom-dwelling sharks. Deep sea species also tend to have bigger eyes to maximize light absorption at depths. However, all sharks have remarkably complex eyes extremely well-adapted to their environment and predatory behavior!
Common Shark Eye Colors
Black
Many species of sharks, including great white sharks, tiger sharks, and bull sharks, have black eyes. The black color comes from a layer of denticles or placoid scales that coats the surface of the eyeball, acting as a kind of natural sunglasses for the shark (Florida Museum).
This helps cut down on glare and reflection when hunting prey in bright, sunlit water near the surface. Pretty nifty, right?
Since sharks don’t have eyelids, the black coloration helps prevent too much sunlight from entering the eye and potentially damaging the retina. It’s nature’s built-in glare reduction technology! Scientists believe that having mostly black eyes may also assist some shark species with depth perception and contrast when seeking prey or scoping out potential threats.
Green
Unlike black-eyed sharks that hunt near the surface, sharks living in the moderate to dark zones of the ocean often have green eyes. This includes species like nurse sharks, wobbegongs, and angel sharks that spend much of their time resting on the seafloor rather than actively chasing prey.
The green color is better suited to the ambient blue-green light that filters down from above, allowing these sharks to spot food and other objects with greater visual clarity.
There may also be a biofluorescence factor involved. A recent study found that swell sharks have fluorescent green eyes that glow brightly under blue light thanks to special retinal proteins. This unique adaptation lets them see contrast better where sunlight barely reaches. Talk about awesome!
Blue
Believe it or not, some deep sea shark species have brilliant blue eyes that shine like sapphires in the darkness! No one is exactly sure why, but scientists speculate that at depths of 3,000 feet or more, blue eyes may enable enhanced light sensitivity compared to greens or blacks.
The leading theory is that they absorb what little sunlight filters down while also harnessing the bioluminescence of marine creatures in the abyss.
Examples of deep sea sharks with azure eye coloration include the cookiecutter shark, ghost shark, and goblin shark. Their eyes almost seem to glow an otherworldly neon blue against the pitch black waters, giving them an alien appearance. Spooky but totally awesome!
Yellow/Brown/Grey
Not all sharks have such dynamic-sounding eye colors. Some sharks that inhabit intertidal zones and river mouths near land have yellowish, brownish, or grey eyes. These include species such as speartooth sharks, river sharks, and zebra sharks.
Compared to the bold colors sported by their purely ocean-dwelling relatives, these shoreline sharks have rather plain eye shades. Scientists think that yellow, brown, and grey eyes are well-suited to the more sedimented waters they frequent, which filter out wider color spectrums of light.
This adaptation allows them to spot food and predators in the muted underwater hues.
In a recent survey of juvenile zebra sharks, over 90% had grey or yellow eyes, with a handful displaying an eye color described as “light ruby.” So even among the mundane shades, there is some variation!
What Causes Variations in Shark Eye Color?
Adaptation to Environment
Sharks inhabit a wide range of marine environments, from shallow coastal regions to the dark depths of the open ocean. To thrive in these varying conditions, different shark species have evolved diverse eye colors and visual systems (Florida Museum).
Sharks that dwell in well-lit shallow waters often have eyes with a golden, greenish, or silvery hue. These colors allow their eyes to camouflage against the sun-filled environment. Meanwhile, sharks residing in deeper zones below 200 meters have completely black eyes that effectively absorb the minimal light available.
A shark’s iris pigmentation and retinal cell density also adapt to ambient light levels. Coastal sharks have higher concentrations of retinal cells to discern prey movements in brighter settings. Comparatively, deep sea sharks have additional pigments in their irises to detect whatever little light exists in the stygian darkness (ScienceDirect).
Therefore, eye color variation allows different shark species to see clearly in their respective habitats, conferring better hunting and survival capabilities.
Dietary Pigments
The types of prey sharks consume can also influence their eye color over time. Sharks are generally either fish eaters or squid eaters. The carotenoid pigments abundant in fish can accumulate in shark ocular tissues, lending their eyes a yellowish to orange hue.
In contrast, sharks with dark brown to black eyes predominantly feast on squid and other cephalopods containing melanin. One study found that great white sharks with darker eyes had triple the melanin concentration compared to lighter-eyed individuals, reflecting their greater intake of melanin-rich squid (Journal of Experimental Biology).
So a shark’s eye color can offer clues about its nutritional habits!
Additionally, some deep sea shark species have a green bioluminescent tapetum lucidum lining the back of their eyes. This reflective layer magnifies incoming light to enhance vision in nearly pitch-black waters.
Researchers speculate this glowing green color originates from luciferins, pigments produced by the shark’s diet of small fish and crustaceans capable of bioluminescence (ScienceDaily). So by literally being “what they eat”, sharks have adapted mechanisms to brighten their sight in the eternal darkness of the bathypelagic realm.
| Shark Species | Eye Color | Diet |
|---|---|---|
| Great white shark | Black | Mainly squid and fish |
| Tiger shark | Greenish-yellow | Fish, turtles, seabirds |
| Cookiecutter shark | Dark brown | Squid, fish, cetaceans |
As shown in the table, differences in dietary intake of pigmented prey manifest in the varied eye colors seen across shark species. This diversity equips them for optimized vision to succeed as apex ocean predators.
Unique Shark Eye Adaptations
Nictitating Membrane
One unique adaptation that helps sharks see underwater is the nictitating membrane. This transparent or translucent third eyelid helps protect and moisten the eye while allowing sharks to maintain their vision. When a shark attacks prey, the nictitating membrane covers the eye to prevent damage.
It also clears away debris and spreads tears across the eye.
Researchers believe the nictitating membrane gives sharks exceptional visual clarity under water. As they scan for prey or assess surroundings, the membrane keeps the eye moist and debris-free without obstructing sight.
Some experts think the membrane even helps sharks judge distance accurately when biting and capturing food.
Pupil Shape
Another unique shark eye feature is the pupil shape. Unlike the round pupils of humans, sharks often have pupils that contract to vertical slits or even small pinholes. This shape controls how much light enters the eye, especially in bright conditions closer to the water’s surface.
By narrowing their pupils to small slits or points, sharks can avoid overstimulation as daylight filters down. This adaptation allows them to swim and hunt at various depths without being blinded. Some deep sea species even have bioluminescent organs near the eye to produce light whenæ·±water diving in darkness.
Eyelids
Interestingly, sharks lack traditional movable eyelids that open and close to spread lubrication across terrestrial animals’ eyes. Because they dwell underwater, the ocean environment already keeps their eyes moist.
Instead, sharks have evolved a nictitating membrane that operates as a protective third eyelid while maintaining vision.
Species like the bull shark are exceptions, however, with the ability to swim far up brackish and freshwater rivers. On rare occasions, these amphibious sharks have been caught blinking. Researchers believe it may help keep their eyes hydrated when visiting habitats above surface.
But for most sharks, the nictitating membrane alone suffices underwater.
Conclusion
To summarize, most sharks tend to have black eyes, which allow them to see well in dark or murky waters. However, some species exhibit different eye colors like green, blue, yellow, brown, or grey based on adaptations to their environment and diet.
The unique structure and capabilities of the shark eye have evolved to make these aquatic predators effective hunters.
