| Name | Seals | Diet | Carnivorous |
| Scientific name | Phocidae | Weight | 4,000 kilograms (8,800 pounds) |
| Pronunciation | seel | Length | 1.17 to 5.8 meters (3.8 to 19 feet) |
| Classification | Mammalia, Carnivora, & Pinnipedia | Location | Northern Hemisphere |
The Seal
Seals are arguably the most popular marine mammals after whales.
The true seals are commonly referred to as earless seals to distinguish them from the broader group of seals, which includes walruses and sea lions.
Despite the name, true seals are technically not earless.
They lack an external ear but still have ear holes and can perceive sound.
They spend most of their life at sea, hunting fish, crabs, squid, octopuses, and other marine invertebrates.
They’re great divers, but they come on land frequently to mate, give birth, or escape from predators.
Most species of true seals live in the Northern Hemisphere.
However, a few of them have also been found south of the equator.
Humans have hunted them for hundreds of years and are still being actively hunted.
This and other factors have led to the decline and near extinction of some seal species.
In this article, we’ll provide a detailed overview of this marine mammal to understand its uniqueness better.
Taxonomy and Classification
Any of the 32 species of web-footed aquatic mammals in the Pinnipedia clade are collectively referred to as seals.
However, the true seals are members of the family Phocidae.
They’re also called earless seals to distinguish them from other pinnipeds, such as walruses (family Odobenidae) and eared seals (family Otariidae).
They are sometimes referred to as crawling seals as well because they crawl awkwardly on their bellies, compared to other pinnipeds whose hindlimbs are better developed.
Phocids belong to the order Carnivora.
Unlike whales that evolved from hoofed terrestrial mammals, phocids evolved from carnivorous ancestors distantly related to modern bears and mustelids.
The likely common ancestor of all seals is the Enaliarctos, which lived from the Oligocene to the early Miocene period about 24 to 22 million years ago.
There are about 14 genera of seals found in oceans worldwide.
Some of the most notable ones include:
- Gray seal (Halichoerus grypus)
- Ribbon seal (Histriophoca fasciata)
- Harp seal (Pagophilus groenlandicus)
- Ringed seal (Pusa hispida)
- Harbor seal or common seal (Phoca vitulina)
- Northern elephant seal (Mirounga angustirostris)
Physical Characteristics
The true seals (Phocidae) are medium to large-sized marine mammals with a rotund but streamlined body.
Their bodies are elongated and taper towards the rear, giving them a torpedo-like shape.
All four limbs are modified to form flippers, which are used for swimming.
The fore-flippers are small, while the rear flippers are larger.
They vary in size depending on the species.
Their size can range from about four feet for the ringed seal to roughly 20 feet for larger species like the elephant seals.
Some species, such as the southern elephant seal, weigh as much as 8,800 pounds, which makes them the largest living member of the order Carnivora.
All seals have a thick layer of blubber under their skin.
This provides insulation and helps them regulate their body temperature in the cold waters where they’re typically found.
Seals have highly sensitive whiskers, or vibrissae, on their faces.
These whiskers are packed with nerve endings and help them detect prey underwater.
They can sense vibrations and changes in water pressure, aiding in hunting.
The phocids have no external ear flaps, one of their most distinctive attributes distinguishing them from other types of seals.
The lack of external ears helps reduce drag in the water, making them efficient swimmers.
Their nipples are retractable, their testicles are internal, and their penile sheath is internal, further streamlining their body.
The coloration of seals can vary between species, but it often includes shades of gray, brown, or tan.
Their coloration provides camouflage in their specific habitats, helping them blend in with rocks, ice, or the ocean’s surface.
Some species, such as hooded and spotted seals, have distinct patterns or markings on their skin.
Habitat and Distribution
Most true seals are found in the Northern Hemisphere.
However, a few species live south of the equator.
Most phocid species are circumpolar, which means they live at or around the poles.
However, some species, such as the gray, harbor, and elephant seals, live in more temperate regions.
The three species of monk seals (Neomonachus and Monachus genera) live in tropical or subtropical regions.
They’re found in the Caribbean and Mediterranean Sea as well as the Pacific Ocean.
True seals mostly live in shallow marine habitats but can also venture into the open water and deep marine environments.
The respiratory and circulatory system of the phocids is specially adapted to swimming at considerable depths.
Like other marine mammals, they still have to come to the surface for air, but seals can spend considerable amounts of time underwater in between depths.
They typically surface every three minutes but can stay underwater for up to 30 minutes if they want to.
When seals dive, they force air from their lungs to their upper respiratory passages.
This protects them from decompression sickness in the high-pressure environments that they dive into.
When they’re not at sea, seals spend their time on drifting ice, marine islands, and some mainland beaches.
Behavior and Social Structure
Seals are carnivorous mammals that feed primarily on a diet of fish, cephalopods, and other marine invertebrates.
Seals are skilled hunters underwater, thanks to their highly streamlined bodies.
While the eared seals and walruses are known for their speed and maneuverability, phocids swim more efficiently for long distances.
This allows the true seals to forage farther away from land than other seals.
Seals swim by moving their body sideways rapidly while using their hand flippers for steering.
Their hind flippers are fused to their pelvis and cannot bend underneath their bodies.
Consequently, seals move very clumsily on land, which is why they’re called crawling seals.
Most seal species are solitary and prefer to hunt and rest alone.
They may tolerate the presence of other seals but do not form strong social bonds.
This changes during the breeding season when seals gather in large groups or colonies.
Breeding colonies can be formed by up to a thousand individuals.
Some species, such as the gray seal, have a harem-based social structure within these colonies where a dominant male gets to mate with multiple females.
These males tend to be aggressive and will actively defend their harems against rival males.
Many seal species exhibit seasonal migrations in search of food or breeding sites.
These migrations can be local, within a specific range, or long-distance, covering hundreds of miles.
Unlike walruses and eared seals, true seals don’t communicate by barking.
Instead, they grunt and slap the water to communicate with other seals.
Seals are generally crepuscular or nocturnal.
This means they’re more active at dawn, dusk, or at night.
During the day, they can be found resting on haul-out sites, where they bask in the sun to warm up and conserve energy.
Diet and Feeding
The phocids are carnivorous mammals.
Generally, they’re considered opportunistic predators, which means they consume pretty much any marine organisms, depending on what’s available within their territory.
Fish forms a significant portion of the diet of most seal species.
The specific types of fish they consume depend on their specific geographic location and habitats.
Seals are also skilled at capturing squids and other cephalopods.
Some seal species, like the crab-eater seal in the Antarctic, are specially adapted to hunting krill and other small crustaceans.
Seals are well-adapted for hunting underwater.
The sensitive vibrissae (whiskers) on their faces help them detect prey in the water by sensing vibration and changes in water pressure.
Seals are capable of deep dives, often reaching considerable depths in search of prey.
Although they’re carnivorans, phocids have fewer teeth compared to their land-based relatives.
They do have powerful canines, which are efficient for gripping and cutting into prey.
Many species lack chewing teeth, which means they have to swallow their prey whole.
The seal’s throat can stretch to accommodate prey items that may seem too large for their mouths.
Seals have a thick layer of blubber that acts as a store of energy for extended periods when food is scarce.
This adaptation allows them to survive during long foraging trips or when fasting during the breeding season.
Reproduction and Life Cycle
Seals spend most of their time at sea but return to their breeding sites during breeding season.
Breeding sites are typically on land or sheets of pack ice.
Before the mating season begins, the female spends her time foraging actively to build up fat reserves.
That’s because their breeding site is often hundreds of kilometers from their typical hunting grounds, so they have to fast for long periods during this season.
The specifics of mating rituals vary among seal species.
In most cases, males compete for access to females during the breeding season.
Dominant males get the best harem and breeding sites, with the right to mate with multiple females.
Courtship displays also vary from one species to the other.
For example, male elephant seals have an inflatable, trunk-like nose, which they use to produce loud calls that help them establish dominance over other males.
The gestation period (pregnancy) lasts for several months.
It can range from as short as three to four months in some species, such as common seals, to as long as 11 months in elephant seals.
Mother seals give birth to one pup.
The pup is typically born on breeding grounds during the spring season.
Pups are fed energy-rich milk from the mother, which helps them gain weight rapidly.
The pup will remain with the mother for about four to six weeks before weaning.
In some species, like the hooded seal, the lactation period lasts only about five days.
After the nursing period ends, the mother abandons her pup at the breeding site in search of food.
There are records of pups suckling from unrelated females.
Such pups are referred to as milk stealers, and this act often results in the death of the mother’s actual pup since females only have enough milk to sustain just one pup.
Seal pups that have been abandoned by their mothers may remain at the breeding grounds for several weeks.
During this period, which may last up to 12 weeks in some species (like the northern elephant seal), the pup neither eats nor drinks.
After this post-weaning period, the juvenile pup starts hunting for its own food and will eventually leave its natal breeding site.
Ecological Role and Interactions
Seals are the top predators in their marine ecosystem.
They prey on various animals, including fish, squid, and crustaceans.
The feeding activities of this carnivorous mammal help to regulate the population of these prey species and ensure the balance of their ecosystem.
For instance, seals play a role in maintaining healthy kelp forests in some regions.
Feeding on herbivorous marine organisms such as sea urchin seals prevents the overgrazing of kelp forests, which is vital for the survival of various marine species.
Other animal species, such as seabirds, may follow seals as they hunt, taking advantage of the seal’s ability to stir up prey.
Seals themselves are prey for larger marine predators such as sharks, orcas (killer whales), and some species of large sea lions.
These predators rely on seals as an essential food source within the marine ecosystem.
Conservation Status and Threats
The conservation status of phocids varies from one species to the other.
Although several species are currently listed as “Least Concern” on the IUCN Red List of endangered animals, many of them are also listed as “Threatened” or “Endangered.”
The Caspian seal, Hawaiian monk seal, and the Mediterranean monk seal are examples of seal species currently listed as “Endangered.”
Seal hunters have long targeted seals for their fur and blubber, which have driven some species to extinction.
The Caribbean monk seal, for instance, went extinct in the 1970s due to these hunting activities.
To protect this species, various governments have introduced regulations to limit seal hunting.
Yet, seals still face significant threats from human activities.
Even when they’re not targeted specifically, seals may get entangled in fishing nets.
Climate change is arguably the biggest threat faced by seals these days.
This is particularly true for seal species that depend on sea ice for survival.
For instance, ringed seals make caves in the snow, and the fact that snow melts earlier than usual due to climate change puts them at greater risk of predation.
Unique Adaptations and Survival Strategies
Seals have streamlined, torpedo-shaped bodies that minimize water resistance as they swim.
The fact that they’re earless is particularly beneficial as it allows them to move efficiently through the water.
This helps to conserve energy during long-distance swims.
Seals have a thick layer of blubber under their skin.
Apart from insulation, the layer of fat also stores energy, which helps them fast during the breeding season and lactation periods.
Cultural Significance and Human Interactions
Seals have played essential roles, especially in the cultures of indigenous peoples in regions where seals are pretty abundant.
The Inuit, Yupik, and other Arctic indigenous cultures lived alongside these marine mammals for thousands of years and have a deep connection to them.
In many of these cultures, seal meat, fur, bones, and other parts of their body provided sustenance.
Seals and other marine mammals also feature prominently in indigenous mythology and folktales in these regions.
Seal hunting is a practice that has endured into modern times.
It used to be prevalent, but commercial seal hunting has recently faced significant controversy and opposition due to overexploitation and its impact on the seal population.
These practices have been regulated or completely banned in many countries to protect seals.
Seal-watching tours and ecotourism are popular activities in regions where seals are abundant.
They are also commonly domesticated and can be observed in zoos, or marine animal shows where they’re kept for entertainment.
Future Prospects and Research
Most studies relating to seals have focused on conservation efforts.
Scientists have been applying different methods, such as remote sensing and tracking, to get more data on seal population trends and the threats they face.
Studies on seal foraging behavior are also quite common.
Scientists also try to examine the physiology of these marine mammals, particularly their adaptations to extreme aquatic environments and their ability to fast for long periods.
Findings from this research provide insights into human thermoregulation, tissue oxygenation, and so on, with potential applications in medicine and physiology.
Conclusion
The true seals are marine mammals in the family Phocidae.
They’re closely related to other marine mammals within the Pinnipedia group but differ from them by being earless and having hindlimbs that are too fused to be useful for locomotion on land.
Seals are primarily found in the Northern Hemisphere, with a predominantly circumpolar distribution.
However, some populations also live in tropical and temperate waters worldwide.
Seals were actively hunted in the past for their fur, meat, and blubber.
Stringent regulations have helped to protect them from these human activities.
However, seals are still at risk of climate change and other environmental factors that put them at risk of decline and possible extinction.
Sources :
- https://www.pbs.org/wnet/nature/blog/seal-fact-sheet/
- https://www.britannica.com/animal/seal-mammal
- https://en.wikipedia.org/wiki/Earless_seal
- https://en.wikipedia.org/wiki/Pinniped
- https://www.worldwildlife.org/species/seals
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