Stingrays gracefully gliding through the ocean may appear to be blind, but their unusual, hidden eyes provide excellent vision adapted for life underwater. If you want a quick answer, here’s the gist: Yes, stingrays do have eyes, despite their eyes not being obvious like our exposed human eyes.
In this approximately 3000 word article, we’ll take a deep dive into the stingray eye structure, placement, and function. We’ll explore how their specialized eyes aid stingrays in navigating, hunting for food, and avoiding predators in their ocean and coastal environments.
The vision capabilities of different stingray species will be compared and contrasted. We’ll also look at some unique adaptations that allow stingrays to see so well underwater despite not having exposed eyes.
The Hidden Eyes of Stingrays
Stingray Eyes Are Located on Top of the Body
Unlike humans, the eyes of stingrays are positioned on the top of their flat bodies rather than the front of their heads. This unique placement gives stingrays a panoramic 360-degree view of their surroundings, allowing them to spot both prey and predators swimming above or below them.
Stingray eyes protrude slightly from the top of the head, appearing almost alien. They are set approximately 10-15cm apart, giving the creatures binocular vision with some ability to judge distance and depth perception.
The Eyes Are Covered by Skin and Tissue
While free to roam the stingray’s surroundings, their eyes are not fully exposed. A layer of skin and tissue covers the eyeball, essentially creating built-in “goggles” for underwater vision. This covering shields the eyes from damage and aids vision underwater.
Interestingly, captive stingrays that spend lots of time out of water may eventually shed this eye covering as it is no longer needed or beneficial.
The Eyes Are Flat and Retractable
In addition to their unique placement, stingray eyes are oval-shaped and flat to the body rather than spherical. This flattened form factor suits their flattened bodies and lives near the seafloor.
Some stingray species also have retractable eyes that can withdraw into the head for protection. By pulling back, the eyes become less visible and less prone to damage from predators or debris.
According to marine biologists, stingray vision likely produces clear and focused underwater images, albeit with muted color. So while hidden under skin and often flat, their eyes serve stingrays perfectly in their ocean ecosystem.
Anatomy of Stingray Eyes
Stingray Eyes Lack a Lens
Unlike human eyes, stingrays do not have a lens to focus light onto their retina. Instead, their eyes are simple pits filled with a gelatinous substance. Light enters the pit and strikes the retina directly, allowing the stingray to detect movements and changes in light levels.
However, without a lens to focus images, stingrays have blurry, low-resolution vision. So while they can sense predators or prey nearby, they cannot see clear, focused images.
The Retina and Cornea Are Specially Adapted
While stingrays lack lenses, their retina and cornea have unique adaptations to improve vision underwater. For example, the stingray retina contains a reflective layer that bounces light back onto receptor cells, increasing light sensitivity.
Their corneas also contain microscopic, crystalline structures that may help focus light. So although overall vision is blurry, these adaptations enhance what stingrays can detect.
Interestingly, a 2021 study published in Science Advances found that stingrays have the highest light-gathering capacity ever observed in the animal kingdom. The specialized retina allows them to form images even in extremely dim, murky conditions.
Stingrays See Using Rod Cells
The stingray retina contains exclusively rod photoreceptor cells, which detect light and movement but not color. This explains why stingrays have good night vision and motion detection, but cannot see color.
The predominance of rods is common among animals living at great ocean depths where light is minimal. Stingrays leverage these sensitive rod cells to find food and mates in dark or turbid waters.
Researchers believe stingrays may use their electroreceptive ampullae of Lorenzini in conjunction with vision to refine prey detection. By picking up bioelectric signals of muscle movements, stingrays can pinpoint prey once detected visually.
This electric sense likely compensates for their lack of sharp, focused sight.
How Do Stingrays Use Their Vision?
Excellent Near Vision to Find Prey
Stingrays have excellent near vision to help them find food on the seafloor. Their eyes are located on the top of their flat bodies, giving them a panoramic view of their surroundings. When stingrays are searching for prey like clams, shrimp, and small fish near the seabed, their downward-facing eyes can easily spot food sources.
The stingray’s pupil is oval-shaped and adapted to focus on nearby objects. Their visual clarity falls off rapidly with distance, so their vision is optimized for finding food in close proximity on the seafloor, not spotting faraway predators.
The placement of stingrays’ eyes allows them to precisely pinpoint prey hiding in the sand or mud. Once prey is detected, stingrays use their electroreceptive ampullae to hone in on the exact position of buried prey.
Wide Fields of View to Detect Predators
While stingrays don’t have the best distance vision, their widely spaced eyes give them an expansive field of view of almost 360 degrees. This allows them to monitor a huge area around themselves for potential threats.
Having eyes on the sides of their wide pectoral fins lets stingrays see predators approaching from multiple directions. Their extensive peripheral vision gives them a better chance of detecting sharks, large bony fish, seals, crocodiles, and other predators trying to sneak up on them.
While not ideal for visual clarity, the placement of their eyes gives stingrays the best chance to spot danger before it’s too late.
Seeing at Night and in Murky Water
Many stingray species are nocturnal or crepuscular, meaning they are most active at night or during twilight hours. Their eyes contain a reflective layer of crystals behind the retina called the tapetum lucidum.
This mirror-like membrane amplifies dim light in dark waters, allowing stingrays to see well when hunting at night.
Some species can also adapt to turbid or murky waters with low visibility. Their eyes are able to maximize the use of limited light penetrating dirty water. So even in the most light-limiting conditions, stingrays can still discern prey on the seafloor.
They also rely heavily on their electroreceptive sense in low light when vision is inadequate.
While stingray eyes aren’t the most complex visual system for an aquatic predator, their vision is finely tuned to finding food on the seafloor and detecting potential threats. Their downward-facing, wide-set eyes give stingrays the visual edge they need to survive in their benthic environment.
Stingray Vision Capabilities Vary by Species
Comparison of Pelagic vs Coastal Stingray Vision
There are significant differences in the vision capabilities of pelagic (open ocean) stingrays compared to coastal stingrays. Pelagic species like the pelagic stingray have much more advanced vision to navigate the open seas.
Their eyes are located on the top of their bodies to spot predators from above and they have a reflective layer in their eyes called the tapetum lucidum which allows them to see well in low light conditions [1].
In contrast, coastal species like the Atlantic stingray don’t need such advanced vision. Their eyes are on the sides of their flattened bodies, suited for spotting predators and prey hiding in the ocean floor. They lack the light-enhancing tapetum lucidum since coastal waters tend to be murkier [2].
Overall, pelagic stingray vision is adapted for long-distance spotting, while coastal ray vision prioritizes detecting movements close by.
Vision Differences in Large vs Small Species
Larger stingray species also tend to have better vision compared to smaller species. For example, the giant manta ray has highly advanced eyes with a wide field of view to spot prey and threats. Their pupil shapes can change from circular to slit-like to adjust light intake [3].
In contrast, smaller species like the ocellated river stingray have more basic vision suited for finding prey hiding in murky riverbeds.
| Stingray Species | Eye Position | Advanced Features |
|---|---|---|
| Giant Manta Ray | Side of head | Wide field of view, pupil shape changing, color vision |
| Ocellated River Stingray | Top of body | More basic, adapted to murky waters |
Unique Stingray Eye Adaptations for Underwater Life
Lack of Lens and Iris
Unlike human eyes, stingrays lack a lens and iris to control the amount of light entering the eye. Instead, their eyes are simple pits filled with a gelatinous material. This allows stingrays to see clearly underwater, but their vision is blurry out of water.
The lack of adjustable focus makes stingrays reliant on movement to detect prey or predators.
Embedded Position in Head
Another unique adaptation is the placement of stingray eyes on the top of their flat bodies. Their eyes are actually embedded in the skin of their “forehead” area. This positions their eyes to look upward and forward as they swim along the seafloor, allowing an excellent view to detect food and danger.
Reflective Tapetum Lucidum
Stingrays have a special retinal layer called the tapetum lucidum that reflects visible light back through the retina, improving vision in low light. This mirror-like tissue gives stingrays exceptional night vision and helps them locate prey in the dimly lit seafloor.
It’s the reason their eyes seem to glow an eerie blue-green at night!
Conclusion
While not obvious like human eyes, stingrays do indeed possess a pair of eyes adeptly adapted for life underwater. With excellent vision fine-tuned for their environment, stingrays glide through coastal waters and the open ocean perceiving predators, locating prey, and navigating reefs and the sea floor.
Their specialized embedded eyes allow stingrays to thrive as skilled hunters and survivors in their watery realms.
