Seals have many amazing adaptations for their lives in the harsh liminal environment between land and sea. They are expert divers and expert nappers (they sleep on land and in the water), they withstand battering waves, cold and dark conditions, and they look adorable while doing so. Explore this interactive unit of seal and click the fish to find out more!
![Seal](https://sealsignal.org/wp-content/uploads/2025/07/BIG-SEAL-backgroundgrey.png")
Sealed for Success: Semi-Aquatic Anatomy
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Seal whisker science
For us to find out about the phenomenal abilities of seal whiskers, seals have participated in a variety of sensory experiments. Scientists designed tests where the seals wear coverings over their eyes and ears, leaving only their whiskers to guide them. Even so, they are able point out the direction of water currents and can trail a mechanical fish through the water.
These experiments revealed that seals can track the path of a fish even through choppy waters and swirling jets. Their whiskers are so sensitive, they pick up the faint turbulence left in a fish’s wake.
Much of this groundbreaking research about vibrissae was conducted at the Marine Science Center with the help of harbor seals!
If you want to follow the trail of knowledge and take a close look at the biomechanics of vibrissae, let your brain bask in this sealiously smart study.
Counting whiskers
The number and arrangement of vibrissae vary not only by species but also between individuals of the same species. Harbor seals, for instance, typically have around 44 mystacial vibrissae, arranged in seven neat rows on each side of the snout. Above the eyes, supraorbital vibrissae (eyebrow whiskers) range from three to seven on each side, with noticeable variation between individuals. Only true seals possess additional rhinal vibrissae: two to four whiskers located just above the nose.
Most whiskered of all are bearded seals and walruses, which can have up to 700 vibrissae.
Whiskers
Seal whiskers, or vibrissae, are uniquely shaped and extremely sensitive. They allow seals to detect the subtle movements of fish that passed by minutes earlier and even assess whether the prey is worth pursuing. This makes them invaluable for hunting in dark, murky waters.
Vibrissae are located on the sides of the snout, above the eyes, and on the nose, giving the seal nearly 360 degrees of sensory coverage. Unlike what you might expect, these whiskers don’t flatten against the face when a seal swims quickly. Instead, their special wavy structure minimizes water resistance and allows them to remain extended, functioning even at high speeds. Just like their fur, vibrissae are shed and replaced during the annual molting season.
Seals have lots of muscles to control their whiskers. When you observe a seal underwater (and even on land), and they sense something interesting, you can see how their whiskers are all pointed out to get the best out of this sensory wonder!
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Seals and cataracts
In aquariums and sanctuaries older seals are often observed developing eye issues like cataracts – clouding of the eye lens that can impair their vision. While their incredible whiskers help compensate, seals with impaired sight may need adapted training routines and more attentive caregiving to navigate their surroundings comfortably.
The underlying causes of these eye issues in captivity are still being explored. One likely factor is longevity: seals in human care often live much longer than their wild counterparts thanks to medical and nutritional support, giving age-related conditions like cataracts time to develop.
Another contributing factor could be environmental. In the wild, seals are adapted to the dim blue light of deeper waters. In contrast, captive pools are usually shallower and allow more ultraviolet (UV) light to penetrate and reflect, a known cause of cataract formation across many species. Additionally, captive seals spend proportionally more time on the surface compared to their wild counterparts and get more sun exposure.
To help reduce the risk of UV-related eye damage, some sanctuaries and zoos are exploring mitigation strategies like installing shade structures over pools or using UV-filtering materials in enclosure design. These adaptations aim to mimic the dimmer underwater lighting conditions seals are naturally built for, offering a little extra comfort for their aging eyes.
Eyes
Seal eyes are built for the deep. Oversized and adapted for low-light vision, they help seals navigate dark, murky underwater worlds with ease. A reflective layer behind the retina, called the tapetum lucidum, boosts their night vision.
To protect these sensitive eyes, seals produce a constant layer of mucus. It keeps their eyes moist and guarded against salt, debris, and pressure changes. On land, this coating gives them a glossy, teary-eyed look, and this is actually one of the hallmarks of a healthy seal!
Seal eyes are truly amphibious and adapted to acute sight on land, too, due to their flattened cornea. The change between above water and underwater vision happens in record time.
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Crusty, snotty, but not necessarily sick
While seals can suffer from respiratory illnesses, and thicker mucus or labored breathing may signal an infection, this is not always the case. Other symptoms like lethargy or coughing will be additional pointers, but snotty seals are not necessarily sick seals.
Some species, especially deep-diving ones like elephant seals or Weddell seals, can often be seen with a whitish crust around their nostrils. This is in fact pulmonary surfactant, a substance that helps their lungs rebound after the extreme pressures of a dive. It is an adaptation to the repeated lung collapse and reinflation they experience and thought to be anti-adhesive. During resting periods, exhaled pulmonary surfactant may crust around their nostrils.
Nose
A seal’s nose is built for life below the surface. Unlike humans, seals relax with their nostrils tightly closed – this prevents water from entering while diving. They must actively open them to breathe.
Above water, their noses are surprisingly useful too. Seals have a keen sense of smell, which they use to recognize each other, especially between mothers and pups, and to sniff out clues about their environment.
And sometimes, those nostrils become instruments of communication and hunting. Seals have been seen blowing streams of air bubbles during social interactions and during foraging, using the bubbles to herd fish.
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Tails, flukes, and flippers
Marine mammals have very different ways of propulsion, using different body parts:
When seals swim, they kick their feet – which are the hind flippers! Their tail is tiny and not used for propulsion.
Whales have horizontal flukes at the end of a muscular tail (part of the spine). They swim by moving the tail up and down, unlike fish, which move side to side.
Sirenians (manatees and dugongs) have a paddle- or fluke-shaped rudder, and this is also a tail! Sirenians have no hind limbs, just vestigial bones hidden inside.
So while seals swim with their feet, sirenians and whales swim with their spinal tail. Of these marine mammals, seals are by far the most maneuverable ones.
Tail
Seals do have a tiny, silly tail. It’s located between their two hind flippers and may actually have a purpose on top of being cute:
While the hind flippers do most of the swimming work, especially in true seals, the tiny, often-overlooked appendage still plays a subtle role in maneuvering and communication.
It’s fully mobile and may act as a micro-rudder in the water, helping fine-tune direction during tight turns or slow glides. But it’s also expressive on land, may be part of a seal’s body language and also be used to simply cover sensitive bits of seal anatomy.
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The art of social slapping
Seals are surprisingly expressive with their front flippers, which often act as personal boundary enforcers. They do slap their flippers for asserting dominance, with male grey seals even lifting themselves up on their front flippers to slam into the ground, a vibration carrying across the haul-out site.
But often it’s a question of personal space. If another seal gets too close for comfort on land, instead of picking a fight, many seals perform a determined belly slap. And slapping might not even be needed: a raised flipper is a clear warning sign.
Front flippers are also used to communicate underwater with loud claps, possibly as a signal to other seals or even to attract mates. Scientists are still decoding the acoustic messages behind these gestures.
Front Flippers
A true seal’s front flippers are small, strong, fur-covered and have long claws. On land, they are used for hauling out, clawing onto rocks or ice to lift them up to a safe resting place with the help of their powerful shoulder muscles. In the water, they serve mostly for steering. Ice-dwelling ringed seals shovel subnivean birth lairs into the snow on the sea ice with their front flippers, where their pup is sheltered for its first days in life.
An eared seal’s front flippers are big, skin-covered and have short claws. With their huge surface area, they are used for propelling the seal forward in the water.
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Tucked-in feet for creature comforts
When seals are resting on land, they often strike a pose that’s equal parts adorable and efficient: hind flippers tucked neatly together, tail nestled in between. This isn’t just a nap-time habit.
By drawing their hind flippers close and folding them flat, seals reduce surface area exposed to the cold, helping them conserve body heat when resting on ice or in chilly conditions.
If it’s too hot (or if the sun is shining and they need a “solar panel” to collect some additional heat), they can stretch and open their webbed hind flippers to resemble two big fans.
Hind Flippers
A true seal’s hind flippers are anatomically not a tail, but its “feet”. They are covered with webbing and can fan out to a huge surface area, which is used to propel the seal forward with sideway motions in the water, and for thermoregulation on land.
An eared seal’s hind flippers are smaller and used mostly for steering in water, but eared seals can rotate their pelvis and actually “walk” on land, using their hind flippers as “feet”.
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Can seals get too fat?
Being fat is when seals thrive. And they have evolved to store fat in a way that doesn’t harm their health. Their blubber is subcutaneous and metabolically active, and they don’t suffer from obesity-related diseases like diabetes or heart issues.
The weight of captive seals is closely monitored to keep them healthy, especially since weight loss serves as an early indicator for underlying issues.
Blubber as a target
Blubber unfortunately also became a curse for seals: In the 18th and 19th centuries, seals were hunted en masse not only for their fur, but for their blubber, which was rendered into oil for lamps, leather treatment, and industrial use.
Elephant seals and fur seals were especially targeted, nearly driving some populations to extinction. Even today, seal oil capsules are sold as omega-3 supplements, though this trade is controversial and banned in many countries.
Spekkfinger: When blubber bites back
“Spekkfinger” (literally “blubber finger” in Norwegian) is a real condition, also known as seal finger:
It’s a painful bacterial infection caused by handling seal blubber or carcasses and, above all, being bitten by a seal. Historically, it often led to amputation before antibiotics (especially targeting mycoplasma bacteria leading to seal finger) were available.
Today, it’s rare but still seen in researchers, hunters, and others who work closely with seals, mostly after a bite, and it still needs quick treatment to avoid sepsis.
Blubber
Blubber is a thick layer of subcutaneous fat, insulating the seal against the cold and preserving its energy when diving or when it’s exposed to harsh temperatures.
A seal’s blubber also serves as an energy reserve during fasting periods (like breeding or molting) and provides buoyancy for efficient swimming.
Newly-born seal pups need to gain blubber quick to survive their environment and exposure to water – this is why seal milk has one of the highest fat contents of any mammal milk.
The thickness of the blubber layer changes over the seasons – nursing seal moms lose blubber, for example, basically transfering it to their pup.
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Green seals and red seals
Some seals wear their journeys on their fur, especially when they are due for a molt. Usually, their fur turns a dull brown or grey when it gets old and worn-down, but sometimes algae are growing on their fur, and seals can appear green or yellow-orange as a result, until their old hair falls out and they get a shiny new pelt.
Red or rusty orange seals, on the other hand, are caused by minerals, mostly iron-oxide deposits. Under the right conditions, sediment can aggregate in shallower waters and give the seal’s fur a reddish color. Deeper-diving bearded seals are seeking out the deposits when foraging and often appear rust-colored.
Generally, every discoloration (for example after rubbing against a rusty object) will stay in their fur until their next molt.
Fur
Seal fur is insulating and water-resistant as it’s oily and thick. On land, it is also a protection against the rough rock undergrounds they haul out on.
Some species of seals are born with a different longer fur called lanugo (white fur), which is not very waterproof but insulating against cold, as they don’t have enough blubber yet. In adult seals, the longest fur is seen in fur seals like the Antarctic fur seal with their longer guard hairs, whereas monk seals have the shortest fur, adapted to the (sub-)tropical climates of their habitats.
Seals have to shed their fur regularly and replace it with new fur, sometimes called “catastrophic molt” if they lose all their fur (and even the outer layer of skin) at once. How fast and how “catastrophic” the molt is depends on the species, but most have an annual molting season.
Some true seals have fur patterns of rings and splotches or dots, and their so-called pelage can be used for individual identification, as it’s unique for each seal.
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Umbilical problems for pups
In newborn pups, the umbilical cord is still attached and until and when it falls off, the umbilical site can sometimes become infected, especially if the pup is orphaned or born in rough and stressful conditions. Left untreated, these infections can lead to serious health issues. That’s why early rescue and proper hygiene and check-ups of the umbilical site are so important in rehabilitation centers.
Seal pups can also suffer from umbilical hernias, which can range from relatively harmless to life-threatenting and requiring surgery, if internal organs are affected.
Belly Button
All seals have a belly button (or umbilical scar), a remnant of their time in the womb, just like us. But a look at a seal’s belly button and its surroundings can help determine a seal’s sex, especially in species whithout sexual dimorphism, where males and females look quite similar externally.
In males, there’s a preputial opening (for the penis) located on the ventral abdomen, between the umbilicus and the hind flippers. This is an adaptation to marine life, keeping a streamlined shape and protecting reproductive organs from cold, abrasion, and parasites. In females, there’s no preputial opening. Instead, the genital slit is located between the hind flippers, along with the anus.
So when you’re looking at a seal’s belly, the position and number of openings relative to the belly button can help you tell who’s who.