Sea Lions and Fur Seals: Characteristic, Behavior, Senses, Diving, Reproduction

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sea lions and fur seals, From Animal Spot

Sea lions and fur seals are eared seals (otariids). They have visible earflaps and use all four limbs for walking on land and use their front flippers for swimming. Their rear flippers, which are short and turn forward and backward, are most useful for getting around on land. Eared seals can move much faster on land than seals. The creatures you see doing tricks in marine mammal shows are generally sea lions not seals. The name sea lion is derived from the male’s mane.

Seals and sea lions are carnivorous pinnipeds while manatees and dugongs are called plant-eating sirenians. The difference between a sea lion and a seal is that the former had has flaps over its ears and large front flippers that allow it to maneuver around on land more easily while the latter doesn't. Seals and sea lions have many similarities with land carnivores like dogs and cats such as a long snout and sharp teeth and are thought to have developed from land mammals about 20 million to 25 million years ago. [Source: Roger Gentry, National Geographic, April 1987]

There are 33 species of pinniped, all of which mate and give birth on land and feed at sea. They fall into two categories: true seals and eared seals. True seals (phocids) have no external ear and use their fishtail-like rear flippers for swimming. They are not very mobile on land. They hunch along caterpillar fashion using their whole bodies. Their clawed foreflippers do not offer much help getting around on land.

A male seal lion is called a bull. A female is called a cow. Young are called pups. A group is called a herd, rookery or harem. Pinniped means “fin-footed.” Walruses (odobenids) are neither seals nor sea lions and have no external ear flap but can walk on all fours. Odobenids are the third grouping of pinnipeds.

The origin of seals and sea lions is a matter of some debate. Some say that they evolved separately, with sea lions descending from a common ancestor of weasel. Other say that seals and sea lions evolved together from otter-like creatures. In any case they descended from creatures that once lived full time on land. This is also believed to be the case with whales. Of seal lions and seals, sea lions — with their external ear flaps and more mobile limbs — are most closely related to their land-living ancestors.

Websites and Resources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Fishbase; Encyclopedia of Life; Smithsonian Oceans Portal ; Monterey Bay Aquarium ; MarineBio

Difference Between Seals and Sea Lions

Earless seals such as this Harbor seal here swim with their hind-flippers

Seals and sea lions, together walruses, are pinnipeds. So how are seals and sea lion different? First, seals' furry, generally stubby front feet — thinly webbed flippers, actually, with a claw on each small toe — seem petite in comparison to the mostly skin-covered, elongated fore flippers that sea lions possess. Secondly, sea lions have small flaps for outer ears. The "earless" or "true" seals lack external ears altogether. You have to get very close to see the tiny holes on the sides of a seal’s sleek head. Third, sea lions are noisy. Seals are quieter, vocalizing via soft grunts. [Source: NOAA]

Fourth, while both species spend time both in and out of the water, seals are better adapted to live in the water than on land. Though their bodies can appear chubby, seals are generally smaller and more aquadynamic than sea lions. At the same time, their hind flippers angle backward and don't rotate. This makes them fast in the water but basic belly crawlers on terra firma. Sea lions, on the other hand, are able to "walk" on land by rotating their hind flippers forward and underneath their big bodies. This is why they are more likely to be employed in aquaria and marine shows.

Finally, seals are less social than their sea-lion cousins. They spend more time in the water than sea lions do and often lead solitary lives in the wild, coming ashore together only once a year to meet and mate. Sea lions congregate in gregarious groups called herds or rafts that can reach upwards of 1,500 individuals. It's common for scores of them to haul out together and loll about in the sand, comprising an amorphous pile in the noonday sun.

To sum up, seals and sea lions differ in physical characteristics and adaptations. Sea lions are brown, bark loudly, "walk" on land using their large flippers and have visible ear flaps. Seals have small flippers, wriggle on their bellies on land, and lack visible ear flaps.

Otariidae — Eared Seals

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Eared seals such as the California sea lion here
swims with their fore-flippers

Fur seals and sea lions belong to the marine mammal family Otariidae, whose members are called eared seals, otariid, or otary. Otariidae, one of three groupings of pinnipeds along with Phocidae (true seals) and Odobenids (walruses). Eared seals (Otariids) comprise 15 extant species in seven genera (another species became extinct in the 1950s). They engage in a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. [Source: Wikipedia]

Fur seals and sea lions reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans, the southern Indian, and Atlantic Oceans. They are conspicuously absent in the north Atlantic. Their distribution is complex. In the Pacific, they are found along the North and South American coasts, the coasts of central and northern Asia, and on New Zealand and several other islands, including the Galapagos. In the South Atlantic, otariids can be found along the South American coast and on a number of islands. In the Indian Ocean, they are found only along the coast of SW Australia and on islands.[Source: Phil Myers, Animal Diversity Web (ADW)]

Fur seals and sea lions animals feed on fish, cephalopods, and crustaceans. Otariids are known from as early as the Early Miocene (23 million to 16 million years ago). The words "otariid" and "otary" come from the Greek otarion meaning "little ear", referring to the small but visible external ear flaps (pinnae), which distinguishes them from the phocids.

Sea Lion and Fur Seal Characteristics

Seal lions and fur seals are warm blooded creatures. What keeps them warm in cold water where many of them live is their thick layers of fat, called blubber, under their skin. Fur seals have a thick layer of fur which grows underneath coarse protective hair. But this hair does little to keep them warm when they dive deep in the water. To keep warm in deep seawater and on land seals and sea lions need blubber. Sea lions have relatively thin layers of blubber but have more hair.

Seal lions are not as fully adapted to sea life as whales. They still retain their legs and their heads are similar in shape to those of land mammals. Seals and sea lions have four limbs as opposed to whales and dolphins which have two. The arm and leg bones of seals are relatively short and are contained within the body. The hand and foot bones are elongated and webbed and extend out of the body to form the flippers. The rear flippers can rotate, which allow the animals to move on land and swim with maximum efficiency. Pinnipeds ave fairly long life spans; most live to 20 or more. Sea lions can swim at speeds of 15 miles per hour.

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Steller sea lion bull
There are two kinds of pinniped back limb positions: 1) sea lions and fur seals have forward-pointing back limbs, which allow them to get around better on land. 2) true seals have back limbs pointing backward, which are better adapted for swimming in the open sea. Flippers allow pinnipeds to maneuver around in both water and land.

According to Animal Diversity Web: Sea lions are large, ranging from around 150 kg to over 1000 kg, and males tend to be much larger than females. Their bodies are slender and elongate. Small, cartilaginous external ears are present. All otariids have fur. In the sea lions, relatively coarse hairs predominate, while in the fur seals, dense underfur is also present. Colors are generally shades of brown, without stripes or other contrasting markings. The fore flippers of otariids are long and paddle-like, more than 1/4 of the length of the body. The surfaces of the fore flippers are naked and leathery, and claws are present but small. The hind flippers are also large. They differ from those of true seals ( phocids) in that they can be rotated under the animal when it is on land, partially supporting the body and helping in locomotion. Otariids also have a small but distinct tail. Males have a baculum. [Source: Phil Myers, Animal Diversity Web (ADW)]

The skulls of otariids is bear-like. An alisphenoid canal is present, as are postorbital and supraorbital processes. The occipital condyles are located high on the back of the cranium. The bony part of the eustachian tube is not enlarged. The dental formula is 3/2, 1/1, 4/4, 1-3/1 = 34-38. Postcanine teeth are homodont and generally conical in shape. The first two incisors have a distinctive transverse groove that divides them into two cusps, while the third is canine-like. The canines are large, concial, and curved.

Sea Lion Senses

In dim light, thanks to their large eyes, sea lions and fur seals can see underwater better than humans can on land. Their sharp vision is essential for finding food underwater, especially at great depths.. Sea lions and fur seals have a well-developed sense of hearing in the water. In the air, their hearing ability is greatly reduced. They can also discern higher pitched noises than humans and make a variety of sounds. Seals and sea lions have very sensitive whiskers which they use to track prey. Dolphins use echolocation (emitting sound waves and sensing their reflections to determine the location of objects) to find their prey and navigate their surroundings but researchers had been unable to find evidence that pinnipeds, the group that includes sea lions, had anything similar.

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California sea lion
Sea lions and fur seal vision under water is better than a human's, but a human’s is better on land. Lenses are enlarged and almost round, adapted for focusing on light that is refracted upon entering water. The lenses are not as well-adapted for sight in air. Mucus continually washes over the eyes to protect them. Unlike most land mammals, pinnipeds lack a duct for draining eye fluids into the nasal passages. When a seal lion is out of the water, mucus surrounding the eyes gives them a wet, "tear-rimmed" look. Sea lions and fur seals probably do not have color vision. [Source: Sea World]

Sea lions and fur seals' eyes are adapted for sight in dark and murky water. Like the eyes of other pinnipeds, sea lions and fur seals' eyes contain high numbers of rod cells — photoreceptor cells that are sensitive to low light levels. Sea lions and fur seals have a well-developed tapetum lucidum, a layer of reflecting plates behind the retina. These plates act as mirrors to reflect light back through the retina a second time, increasing the light-gathering ability of the rod cells. (The tapetum lucidum is the same structure that makes a cat's eyes appear to "glow" when reflecting light at night.) Under water, the pupils dilate (expand) into a wide circle to let in as much light as possible. In bright light, the pupils constrict to a slit.

A seal lion uses its sensitive vibrissae (whiskers) to find food, especially in dark, deep waters, or at night. A substantial nerve system transmits tactile information from the vibrissae to the brain. Each vibrissa can move independently. Under water, a seal thrusts its vibrissae to and fro in a sweeping movement by pushing its mobile upper lip in and out.

Seal Lion Behavior and Feeding

Sea lions congregate in the huge rookeries. Most seals do not do this. According to Animal Diversity Web: Otariids tend to be highly social, forming large herds during the breeding season. Within these herds, individual males maintain harems. At the breeding grounds males set up territories, which they defend aggressively. Females arrive and segregate into harems of 3 - 40 individuals, depending on the size and strength of the male. [Source: Phil Myers, Animal Diversity Web (ADW)]

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fur seals
Seal lions may not migrate but they wander far from their colonies in search of food. When they are on land seals prefer to stay on rocky island or points. They “haul out”, or come ashore, to rest. Sea lions express grief. Females have been observed wailing after witnessing their pups being eaten by killer whales.

Seal lions on average consume eight percent of their body weight in food every day. They eat a variety of fish and invertebrates, feeding on schools of small anchovy-like fish, squid, octopus and sometimes lobster. Some eat seabirds. Leopard seals and some sea lions eat seals.

Most females nurse their young for only short time. Even in dense groups seal lions do not form social bonds. Each animal acts on its own behalf, and for its own benefit. Some seal lions are tolerant of humans, even snuggling up next to them, while males occasionally view a human as rival and charge. Bull fur seals weighing 350 pounds have been known to charge people. They have also been know to back off if shouted at loudly enough.

Seal lions can perform many of the same sophisticated learning tasks as dolphins and apes. After a seal lion “has learned words and signals for objects and actions," Roger Gentry wrote in National Geographic. "It can carry out very complex commands such as: Take the large white cube over to the small black ball."

Leo, an eight-year-old male South American sea lion at Hakkeijima Sea Paradise aquarium in Yokohama, Japan, grins and makes facial expression during training and can make the Chinese character for a rabbit and other Chinese zodiac symbols.

How Sea Lions Can Dive 300 Meters and Not Get the Bends

In a study published in the journal Royal Society Biology Letters in September 2012, scientists gave some insight into how sea lions and other marine mammals can dive to 300 meters (1,000 feet) deep in the ocean and hunt for food there without getting the bends — caused when nitrogen gas, compressed in the bloodstream at depth, expands during ascent, causing pain and sometimes death.

Researchers led by Birgitte McDonald at the Scripps Institution of Oceanography captured an female adult California sea lion, anaesthetised the animal and fitted it with loggers to record oxygen pressure in its main artery and the time and depths to which it dived. According to AFP: The 82-kilogram sea lion was then released, and the data from its movements — 48 dives, each lasting around six minutes — was sent back by radio transmitter. At a depth of around 225 meters, there was a dramatic plunge in the sea lion's oxygen pressure, signalling that it had collapsed its lung to shut off additional air (and thus nitrogen) to its bloodstream. Lung collapse in diving mammals is a natural action, in which air-processing alveoli — elastic, balloon-like structures attached to the bronchi — are depleted to reduce the size of the organ. The sea lion kept on diving, reaching a depth of some 300 meters before beginning its ascent.

At around 247 meters, the oxygen pressure rose again, pointing to a reinflation of the lung, and then fell off slightly before the sea lion breached the surface. If the sea lion had collapsed its lung, where did it keep the precious reserve of air to help it survive the ascent? The answer: in the upper airways — the large bronchioles and trachea whose tissues cannot dissolve air into the bloodstream. During the ascent phase, the sea lion draws on this pocket of air to feed the alveoli, the study suggests. At the end of the experiment, the scientists removed the gadgets from the sea lion before releasing it once more into the sea, according to the research, published

Male and Female Fur Seals and Sea Lions

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It is sometimes difficult to determine the sex of sea lion. The pinniped penis and testes are internal. Nipples can be retracted to reduce drag. Size is often the easiest way to tell males and females apart. Sea lion and fur seal males may be five times larger than females by weight. Greater size may give males an advantage in breeding by helping them remain on shore longer where most of the mating takes place. Larger males store more fat, which provides the fuel and water for long fasts.

With its big furry mane and loud belchlike roar you can see how a three-quarter-ton sea lion bull inspired the species name. The weight of an average male fur seal is about 400 pounds, but it can weigh as much as 800 pounds when it returns to land after spending 10 months at sea feeding. Bulls need the extra weight in order to do battle with rival males.

Male seals fight by charging each other. The fights can last for hours. Small males have little chance of winning and often retreat early to the edge of their territory or a neutral area at the head of the beach. The winners, surrounded by their harem, swagger arrogantly and bellow belligerently.

Sea lion males are especially large and ferocious. They have dagger-like canines and fight by slashing at their rival’s neck. Often large quantities of blood is spilt "The full roar of a 600-pound bull fur seal mating season call," John Blazar wrote in the Los Angeles Times, "exploded with a hydraulic vapor cloud, like smoke from a canon. The blast dimples one's eardrum."

Dominant bulls end up with a harem of five to 25 cows while defeated males wander the sea alone until the next breeding season when they try again. A particularly large bull may support a harem of 20 or 30 females who are about one third the male's size.

Sea Lion and Fur Seal Breeding and Sex

Sea lions congregate in the huge rookeries in the mating season. During the breeding season, dominant bulls arrive first at the seal lion’s land gathering area, or colony. They establish territories on sections of beach and keep others away. The dominant bulls force the young bachelor seals to form herds on the periphery of the breeding areas. When the females arrive they gather around the dominant bulls.

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fur seals
According to Animal Diversity Web: Females segregate into harems of 3 - 40 individuals, depending on the size and strength of the male. Soon after they arrive, females give birth to pups from the previous year's breeding season, and within a few days, enter estrous. Mating takes place on land. A period of delayed implantation insures that the young will be born in a year, when the breeding herds again form. [Source: Phil Myers, Animal Diversity Web (ADW)]

Unlike whales, seals and sea lions have not developed the ability to mate and give birth in the sea. Sea lions and fur seals bear their young on land. Finding a good place to give birth and raise young is not so easy. The place should be smooth and sandy and protected from large waves. The sea floor leading up to it should be sloped to make it easy to come ashore. It should also be safe from land predators either on an island that has no such predator or in an area protected by steep cliffs. Places that meet all these conditions are few and far between, which is why often hundreds or thousands of seals gather at such as places where they do exist.

The mating season for sea lions lasts for around two months, at which time the dominate bull is very busy and tired because he is expected to satisfy the sexual needs of all the members of his harem. Sex among sea lions sometimes looks rough and cruel because the male looks so much bigger than the female.

For the one or two month in the mating season, dominant males do nothing but guard their territory, bellow, roar and fight and try to mate with as many females as they can. They don’t go to sea and feed. In many cases they arrive at the beach huge and loaded with blubber and leave exhausted skeletons.

Dominate males jealously guard their harems. Male sea lion get sexually aroused watching other seals have sex. One reason for this is perhaps that so few males get the chance to really do it. Sometimes females mate within 48 hours of giving birth.

Seal Lion Births

Sea lion females arrive on the beach a week or two after the males. They are pregnant with young conceived a year earlier. Within a few days they give birth. Soon after that they become sexually receptive again and are pounced upon by dominate males. Afterwards the females go to sea and feed and return from time to time to suckle their pups. Each female above the age of three or so usually gives birth to one pup each season.

The females do not get pregnant right away. The fertilized egg remains dormant for three months before development begins. The gestation period is nine months. This way female seals can synchronize mating with giving birth, freeing both males and females to spend the rest of the year at sea gorging themselves. The females stay close to the colony where they nurse their young.

Often the cows give birth to a single pup a few weeks after the bulls return from the open sea. The young seal lion are delivered in the territory of the dominant male. A week or so later the male begins mating with females in his harem.

Image Sources: Wikimedia Commons, NOAA

Text Sources: Animal Diversity Web (ADW); National Oceanic and Atmospheric Administration (NOAA); Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.

Last Updated June 2023

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