When we compare sea otters to other marine mammals, we can immediately see the size difference between them and most sea-dwellers. As the second smallest marine mammals, they come shy compared to their neighbor pinnipeds.
So sea otters must have an excellent vision to protect themselves from threats and dangers. They also need their eyes to hunt their prey and eat their catch. More importantly, sea otter moms always need to watch their pups while under their care.
Here at Floofmania, we understand how vision is important to sea otters. So let’s look at their eye structure and how well they can rely on their vision above and below the water.
How Well Do Sea Otters See?
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Sea otters see reasonably well in bright and low light, both in the open air and under the water.
Some scientists also observed the sea otters in Alaska seasonally shift their foraging schedule to daylight hours. It shows that light improves the ability of sea otters to hunt for prey using their vision. They also conserve their energy when they can spot their food more easily.
How Does The Sea Otters’ Eye Structure Contribute To Their Vision?
In a 2020 study, researchers studied the visual adaptations of sea otters in their environments. They observed how each part of a sea otter’s eye contributes to their vision:
The Sea Otter’s Retina
The retinas translate the light that first enters the pupils of the eyes (the black central part of the eyes) into electrical impulses. The image in front of the sea otter will then be processed and recognized once these impulses reach their brains.
Despite not being a nocturnal animal, the sea otters’ retinas have photoreceptors, making the sea otters able to see in low-light underwater conditions. These light-sensitive cells ensure that their eyes gather all the light they can get, especially in the dimly lit underwater surroundings.
The sea otters’ retinas are similar in size to ferrets and domestic cats.
Sea Otters Have A “Tapetum Lucidum” For Low-Light Vision
The tapetum lucida is a membrane that sea otters, along with many other animals, have in the back of their eyes. They act like mirrors that reflect the light that comes through the eyes back to the retinas. These membranes further enhance the sea otters’ visual sensitivity at low light levels.
While we, humans, don’t have this component in our eyes, we can get a glimpse of how it works from our pet dogs or cats. You can simply turn the flashlight on your phone and snap a photo of your pet at night. The tapetum lucidum can be seen from the reflective shine you’ll notice in their eyes.
How Far Can A Sea Otter See?
Sea otters and other marine mammals are actually near-sighted above the water surface.
Sea otters see about 7X less clearly on land than humans with an ideal 20/20 vision. They share this visual characteristic with pinnipeds like seals, sea lions, and walruses.
If you’re someone with a -2.00 or -3.00 graded prescription lens, you see the world a bit like how a sea otter does without your glasses.
In human terms, people with mild nearsightedness (-2.00 prescription) start to have blurry vision for objects more than 20 inches away.
Despite their nearsightedness, sea otters are highly vigilant to disturbances. They are wary of humans and their diurnal natural predators, such as bald eagles and brown bears, because they can contrast color and brightness differences.
Do Sea Otters See Better Above Or Below Water?
While sea otters don’t have a highly acute vision above the water, they have a powerful underwater vision.
Water acts like a corrective lens itself because it refracts light in a different way than air does.
In fact, objects appear 25% closer and 33% larger than they actually are underwater.
Sea Otters Have One Of The Highest Eye Accommodations Among Vertebrates
Sea otters compensate for how the light bends underwater by squeezing their lenses through their pupils into a more rounded shape. It allows the light to reach the retina properly and gives them a clear underwater vision.
This process is called accommodation, wherein the eye’s optical power is changed to keep a clear focus on a particular object, even if it varies in distance.
The terms might be pretty intimidating but just think of an instance when you try to open your eyes underwater. It’ll be pretty blurry if you’re not wearing swimming goggles, right? So with accommodation, sea otters essentially create built-in goggles each time they go for a dive.
And even though humans can also use this technique, sea otters are just more skilled at it than us. Amazingly, their eyes can reach up to 60 diopters, which means they can have a perfect 20/20 vision underwater, unlike us.
Can Sea Otters See Colors?
Yes, sea otters can see colors! Although they are red-green colorblind.
And even though the sea otters’ color vision is limited by the two colors they can’t see, they can actually see more colors than most marine mammals! In fact, the majority of marine mammals are colorblind!
To understand why color perception isn’t necessary for underwater vision, we need to discuss color absorption in relation to water depth:
Things Lose Their Color The Deeper Underwater You Go
Water is about 800X denser than air, which means that water can absorb light very quickly. But the rate at which the water absorbs light depends on the different color wavelengths. Colors with longer wavelengths (shorter energy) are absorbed faster than shorter ones (higher energy).
If you can recall the rainbow colors or know the mnemonic R.O.Y.G.B.I.V, the wavelength goes shorter (slowly absorbed) as the color order progresses. More specifically:
- Red disappears underwater at 15 feet.
- Orange at 25 feet.
- Yellow in 35 feet.
- Green at 70 feet.
- Purple and blue have the shortest wavelengths and highest energy, so they are the last to fade out at about 110 feet.
In the same way, it also answers the question as to why the ocean is blue. The sea filters out the bright colors (red and orange) at just a few feet underwater. As a result, the cool hues (blue, purple, and green) get left behind, which is what our eyes perceive as the natural color of the ocean.
Seals, sea lions, and walruses (pinnipeds) can only see in shades of blue and green underwater. For them, seeing brighter hues wouldn’t benefit them because they dive hundreds to thousands of feet deep into the ocean.
For the same reason, sea otters also have little to no use in seeing the color red (15 feet) and green (70 feet) underwater. They can dive as deep as 85 feet to forage. Still, they routinely do it in just 20 to 30 feet to return for another helping immediately.
|Mammal||Dive Depth||Colors They Can See||Colors They Can’t See|
|Sea Otter||85 feet||Orange, Yellow, Purple, and Blue||Red and Green|
|Pinnipeds (Seals, Sea Lions, Walruses)||1,500, 900, and 300 feet, respectively||Blue and Green||Red, Orange, Yellow, and Purple|
Can Sea Otters See In The Dark?
Sea otters can (sort of) see in the dark.
As mentioned earlier, water absorbs light more quickly than air. So even during the day or when the sun is shining brightly, the light will only reflect on the water’s surface and a few feet underwater. Thus, sea otters will always hunt for food in semi-dark waters.
Sea otters can use their eyes when there’s a bright light or reflection to help them locate non-buried prey in shallow waters. Even in dimmer lighting, sea otters can still detect large objects like kelp or rocks, which may also help their search for food.
However, sea otters are unlikely to use their vision when there’s very low or no light, especially at night. Biologists observed that they have slightly poorer underwater vision than sea lions and seals.
Their eye orbits are noticeably smaller than these pinnipeds, which they believe decreases the sea otters’ visual sensitivity in dark waters.
So while they can’t rely on their eyes in the dark, they are not limited to only a single special sense for any behavior like all living organisms. They will now have to rely on their sensitive paws and whiskers when foraging in the dark or murky waters.
What Do Sea Otters’ Eyes Look Like?
Sea otters have a pair of small, rounded, black eyes.
Like their ears, their fluffy fur might hide their eyes at times.
Sea otter pups already even have their eyes open at birth!
Why Do Sea Otters Rub Their Eyes So Much?
A sea otter rubbing its eyes or face is actually grooming itself to maintain its thick coat’s cleanliness and fluffiness.
Sea otters don’t have blubber like other marine mammals, such as seals and dolphins. So they must rely on their fur to keep them warm and insulated in the cold seas.
When sea otters rub or groom their coat, they drive out the water moisture and scatter the natural oils secreted by their skin into their fur. It helps trap air bubbles that keep them stay afloat on the water’s surface.
Do Sea Otters Cover Their Eyes To Sleep?
Yes, sea otters sometimes cover their eyes with their forepaws when they sleep! Just like this adorable northern sea otter right here:
Some propose that resting their forepaws on their eyes is a helpful position to keep their paws out of the water to conserve body heat. Others also say it helps sea otters quickly fall asleep, especially when the sun is out.
Nevertheless, it gives us more reasons to adore these sea otters from afar!
Why Do Sea Otters Always Have A Tear Under Their Eye?
It may not be noticeable at times, but sea otters can get a tear-like substance under their eyes like this otter right here:
While we can’t give you a definite reason for this phenomenon, here are three theories we’ve gathered from our research:
Sea Otters Could Possibly Have A Harder’s Gland
According to biologists, sea otters have a half-transparent third eyelid that covers their eyes like goggles when swimming. These clear eyelids are more appropriately called the nictitating membranes. They help protect the sea otters’ eyes underwater while still allowing them to view their surroundings.
But these membranes must be moisturized, so the sea otters’ eyes do not dry. And the Harder’s gland supposedly takes care of this. This Harderian gland is attached to the nictitating membrane of tetrapod animals and produces tears or tear film that lubricates their eyes.
Tetrapods are four-limbed vertebrates composed of amphibians, birds, reptiles, and mammals like sea otters! However, there are still no published studies stating whether sea otters have the Harder’s gland in the orbits of their eyes today.
Sea Otters Are Possibly Helping Their Kidneys To Excrete Salt
In humans, we excrete excess salts and other toxic wastes in our bodies through our urine. And we have our kidneys to thank for doing this amazing job tirelessly each day! Similarly, sea otters also filter out wastes through their large kidneys – the largest among any other marine mammal, in fact!
Sea otters need to eat a lot in a day, and their diet primarily consists of salty seafood like their favorite sea urchin and shellfish invertebrates. Because of their high-salt content diet, their kidneys need to handle a lot of excess salts. And some people believe that their tears help their kidneys regulate these salt spikes.
Sea Otters Could Emotionally Cry
Most scientists don’t believe that other animals aside from humans can express their emotions through crying or producing tears. But some researchers observed that sea otters shed tears when irritated or frustrated.
Dr. George W. Steller, a zoologist from Harvard, noticed this behavior in sea otter pups and mothers separated from one another. Whether this is the reason behind the sea otters’ tears or not, we can’t deny the fact that the bond between a sea otter mom and pup is incredibly strong:
Hello! My name is Graciola Galo, but my friends call me “Gra” – so can you! Aside from being a dog lover, my bachelor’s degree in biology has helped me develop a deep appreciation for animals. I look forward to learning more about all kinds of wildlife in every future article I write for Floofmania and I aspire to impart that same awe and wonder to you, too!