“To seal or not to seal, that is the question.”
— A whale that decided to go on a diet the night before but is rethinking its decision in the morning!
The ocean is an extremely different world from the one we live in. It is a balanced ecosystem on its own, one that is so complete, so perfect, and so peaceful. It has no clue what is happening above the water, let alone be aware of the existence of anything other than water in the first place.
There live all sorts of animals, plants, and other organisms whose names are super hard to pronounce. They occupy almost all bodies of water, from oceans, seas, and bays, to rivers, lakes, and streams. Some estimate about 240,000 different species of aquatic animals live in water.
That said, scientists mostly agree that around 91% of these creatures are still unknown to us. On the other hand, the remaining 9% are still pretty overwhelming to study, given that all of them are exceptionally diverse, with many of them being, still, annoyingly similar.
But our job at learningmole.com is to simplify facts as much as possible without messing with their criticality. That is why we are dedicating a series of articles to unveil interesting and vital facts about several aquatic animals. Before, we tackled some distinctive ones, including dolphins, whales and sharks. In this article, we are extending this journey by stepping into the world of seals.
So let’s get started.
Most people are at least a tiny bit familiar with seals.
Seals are semi-aquatic animals. They live in the ocean most of their lifetimes, but they get on land on a regular basis to mate and moult. Seals have flat flippers, which work like fins, to help them dive underwater and feet so they can crawl on land. Like dolphins and sharks, but unlike fish, seals are mammals. So they give birth to live young.
The seals’ physical nature requires them to live in cold climates where the water temperature is typically below 20°C. However, most seals love to live in even colder waters. That is why they are mostly found in and around the poles. That is the North Pacific Ocean, the North Atlantic Ocean, and the Southern Ocean around Antarctica.
Most seals, yes, they are many, are dark grey, with their underparts being whitish. Yet, all seals have facial whiskers, which in turn make them look super cute and innocent, although they are, in fact, predators.
As carnivores, seals feed on meat. Those living in the Antarctic, for instance, prey on penguins. But the killer whale, which is actually a dolphin species, feeds on seals.
That is all cool and so. Yet, one thing might be a little confusing to many. Why does the Internet call many seals, sea lions? Are they the same animal but given two different names?
Well, no. not really. Simply put, seals are not just one animal but many. One of these many is the sea lion. So think of it as an umbrella, a family, below which are many different species. All of these species are classified as seals, and each is given a different name.
That is like the Japanese macaque and the African mandril (Remember Rafiki from Disney’s masterpiece, The Lion King?). They are two different monkey species but have distinct names.
But it does not just end here. So many other things make seals not just exceptional animals but also a swimming miracle. So let’s explore some of these great traits.
As you hopefully remember, the taxonomy hierarchy is used to classify all organisms. It consists of eight ranks: domain, kingdom, phylum, class, order, family, genus, and species.
One order is called Carnivora, which includes all the animals that feed on meat. Below this order are 12 families. Nine out of these 12 are land animals, including cats, dogs, bears, raccoons, otters, skunks, and hyenas. The remaining three families are aquatic, collectively called pinnipeds, or as commonly known, seals.
Pinniped means fin-footed; feet that look like fins. The first seal family is the Odobenidae. It contains only one species, the walrus, which has two super long canine teeth like those that Diego from the Ice Age film franchise once had.
In fact, this walrus used to have many other brothers belonging to the same family, but they went extinct one after another. The walrus itself, although still alive, is facing the risk of extinction.
The second pinniped family is the Otariidae, or the eared seals. Under this family are seven genera, five of which are collectively called sea lions and comprise six species. The other two genera are called fur seals. Together, they have 10 species. All in all, the Otariidae family has 16 seal species.
Finally, there is the Phocidae family, commonly called earless seals. It is further divided into 14 genera, comprising 19 extant species.
To sum up, there are 36 extant seal species. Excluding the walrus, 16 species have ears, and 19 do not.
Aside from ears, all these 36 seal species vary widely in size, appearance, habitat, and behaviour. So let’s explore some of those as well.
All seals have fur. They might also have the same body shape. They are super elliptical, thin at both ends but round and chubby in the middle. That aside, seals do possess many different physical characteristics that set them all apart.
First of all, seals vary greatly in size. The smallest species, the Baikal seal, native to Siberia, Russia, has an average body length of 1.25 metres and weighs between 50 and 130 kg—yes, that is small.
On the other hand, the largest seal species are the northern elephant and the southern elephant seals, with the latter being larger than the former. Both species are also distinct by the fact that males and females are incredibly different.
When it comes to size, at least, the male northern elephant seal weighs from 1,500 kg and up to 2,300 kg and is four to five metres long. The largest recorded northern elephant male weighed 3,700 kg. On the flip side, females only weigh 750 kg and have a body length of 2.5 to 3.6 metres.
That said, the southern elephant males weigh between 1,500 and 3,700 kg and range in body length between 4.2 and 5.8 metres. The largest southern elephant male ever reported was 6.85 metres long and weighed roughly 5,000 kg.
Conversely, female southern elephant seals range between 350 and 900 kg and measure 2.6 to 3 metres. No female has ever reported weight larger than 1,000 kg or body length more than 3.7 metres, at least so far.
In addition to size, seals also vary significantly in their looks. Despite mainly being known for their dazzling dark brown colour, some species, like the harp seal, are white. Some are different hues of grey or brown, and others are even blackish. However, all seals mostly have their underparts of a lighter colour than the back and the rest of the body.
It is not only that. Many seal species are spotted, with every individual having a unique pattern. One species, the ribbon seal, has four thick white stripes on its dark brown body.
As we previously mentioned, the fur seals and the sea lions have ears, while the rest of the species do not.
Luckily for us, the seal fossils scientists found were well-preserved and they taught us a lot about how these animals evolved. The fossil, in fact, was of a land-dwelling animal. This animal is thought to have diverged from the same ancestor as that of bears, raccoons, and cats some twenty-something million years ago.
So what did this ancestor look like?
Well, it was pretty distinct. Its front limbs were short, and its back limbs were webbed, like a duck’s. This proposed the animal must have been a swimmer. This ancestor also had a long tail and short but strong legs. It basically resembled the otter.
This land-dwelling ancestor most probably liked to take daily swims, which lasted longer and longer until it turned, over the course of millions of years, into the aquatic seal(s) we know today.
This transition from land to sea demanded an inevitable transformation of the body of that old ancestor. The most significant changes were turning the hind webbed feet into flippers and shortening the tail. It also underwent several other adaptations to enable diving.
Seals are one valid proof of the saying ‘practice makes perfect’. Although their ancestor lived on land and its swimming skills were barely at the beginning level, its modern-day descendants, all the 36 extant seal species, are great deep-sea divers.
Seals are mammals, and mammals have lungs. So to dive, mammals must hold their breaths. With no prior training, humans can hold their breaths underwater for a maximum of two minutes. Human lungs have the potential to increase this duration with practice.
Take, for example, the British actress Kate Winslet who made a new record holding her breath for seven minutes and 15 seconds while filming Avatar: The Way of Water.
Dolphins are also aquatic mammals. So they typically stay underwater for a maximum of 10 minutes, but they can make it up to 20 minutes if they want to. Penguins, which have lungs, too, since they are birds, can hold their breath for up to 27 minutes underwater.
Seals are much, much more developed than that. Although it differs from one species to another, seals can hold their breaths for 31 minutes and up to two hours, a duration which is achieved by the elephant seals!
The question now is, how on Earth can seals do that?
Well, the several million years of evolution seals went through have changed their entire circulatory system to suit their new aquatic habitat and make them excel at living in it.
The challenge in deep dives is to withstand the great water pressure on the ears and hold breath. Divers usually clear their ears to equalise the pressure in the middle ear with the pressure of the surrounding. The deeper one dives, the greater the water pressure—imagine all that water weight pressing on the tiny little ears!
Well, seals are well adapted to that. Their middle ears have what is called sinuses. These are air cavities that fill with blood and help the middle ear bear the great water pressure and not squeeze.
In addition, seals have more blood, and therefore more red blood cells, than any animal living on land. Those red blood cells are responsible for carrying oxygen from the lungs to every corner of the body. So, seals have more oxygen in their systems and, therefore, can stay underwater for more extended periods.
Furthermore, seals’ hearts are designed to help them stay underwater for long. They slow down significantly to reduce the consumption of oxygen. When diving, seals’ heart rate drops from an average of 100 bpm to almost 10 bpm. This way, they can keep the oxygen in their system even longer.
Another amazing thing about seals is their ability to survive in super-cold waters without freezing. This is thanks to their incredible body composition. Besides their dense fur, seals have a thick layer of fat underneath the skin. It works like a thermal blanket which insulates the entire body from the cold water and confines the heat inside.
Seals also have a high metabolism rate which makes them burn more calories. This activity creates heat and raises their body temperature, helping them stay warm while in water.
All of this is fantastic when seals are in the water, where they normally spend months without even going on land for a sunbath. But what happens when they do? The air is undoubtedly not as cold as the water. So with all these things that keep the heat inside their bodies, seals will surely experience overheating when they get on land.
Well, that does not happen, for seals are equipped with behaviours that help them cool down. For example, they use their flippers to throw cool sand on their backs to cool their bodies. Some species breathe fast to release the heat and cool off.
Seals stay more time in the water than on land. During this time, they play solitary. They live and forage on their own. But they get together when they have to mate, moult (they lose their fur coat and grow a new one), and care for the young until they are developed enough to get in the water.
Like penguins, seals stay in super large groups called colonies when they go on land. Members of the same colony know each other, yet their relationships are not that tight and are often temporary.
Interestingly, males go on land first and wait patiently and excitedly for females to arrive so they can mate with them. When they get on land, females usually stay in clusters where they are approached by males who propose to them. One male seal typically mates with many females per season.
After mating, males often walk away, leaving female seals to care for the young on their own. That is why the strongest social connection is that between females and their young.
When the young are old enough to forage independently, they separate from their mamas, go to the water and start their independent life. This is also when the mama seal returns to her solitary life in the water until it is time to go on land and mate again.
Here we get to the end of today’s article, where we explored some hopefully interesting facts about the fantastic marine animals, seals.
At first, we looked into the seals’ classification. We learned that they belong to the order Carnivora, so they are cousins of cats, dogs, and other land meat-eaters. Internally, seals are divided into several families that include different genera and collectively make the 36 extant seal species. All of these species display differences in size, weight, colours, and habitat.
Then we moved to discuss the seals’ fantastic evolution, where they underwent adaptations to become almost fully aquatic animals, enjoy a super diving ability, and survive in extremely cold environments.
Finally, we looked a little into the seals’ social life. Although they get together to mate and care for their babies, seals mostly live on their own when they are in the water.
We hope you found this article interesting as much as we found it enjoyable to write. Now that you know what seals are, you can learn about another incredible aquatic animal, the dolphin, which also evolved from a land ancestor. Or you can stay in Antarctica and learn about the emperor penguin here.
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