photo credit: Jeff Corwin Facebook page
Australian Fur Seal There are many species of seals named for the fine fur that makes them so attractive to hunters. The large northern fur seal, found in chilly northern waters, was hunted to near extinction during the 19th century. These animals were protected by law in 1911, and populations later rebounded to 1.3 million animals.
There are eight species of southern fur seals, all smaller than their northern relative. They include the Guadalupe fur seal of Baja California, the South African fur seal, the South American fur seal, and the Australian fur seal.
Fur seals have sharp eyesight and keen hearing. They have small ears, unlike the earless or hair seals.
Although they breathe air, seals are most at home in the water and may stay at sea for weeks at a time eating fish, squid, birds, and tiny shrimp-like krill. Fur seals may swim by themselves or gather in small groups.
When breeding season arrives, however, these social animals gather on shore in very large numbers. Powerful males, known as bulls, establish territories and gather harems of up to 40 females, battling their rivals to establish dominance. During this season, coastlines are filled with roaring, growling, honking seals.
Female fur seals, or cows, give birth during this breeding season, then mate again just a few days later. The following year they will return to give birth to a single pup after a nearly yearlong pregnancy, and mate once again to continue the cycle.
Many fur seal populations have not rebounded from extensive hunting, and now face additional threats from climate change and overfishing, which can limit their prey. - National Geographic
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As with whales, dolphins, porpoises, and manatees from last week, seals are another water dwelling mammal. The seals are altogether comfortable there, and wherever cool currents flow and small food animals abound, the finfoots will gracefully dive, leap, and play.
Even though the seal's feet have toes and nails, their wide webs resemble fins. The order of the seal family is Pinnipedia, meaning "fin-footed." These mammals sometimes spend months of every year entirely in the water, but they also pull out on land and shuffle about. Some seals migrate, others feed along the same shorelines every season.
Senses
Sight: to be efficient underwater hunters, seals need to detect and catch prey. Since very little light penetrates at great depths, the eyes of seals are specially adapted to allow them to see underwater. The eyes are especially large – one of the endearing feature of pups – and the lens is structured to allow as much light in as possible. When on land, the eye is protected from bright sunlight by closing the pupil. Thus seals can see well both underwater and on land. Sight is probably more important on land than in the water, and anyone watching common seals will notice that they raise their heads regularly to look for danger.
Hearing: the ears of the seals are also adapted to allow them to hear underwater as well as on land. The bones of the middle ear are larger than in land mammals, and there are changes in the shape and size of other bones in the skull. Sensitivity to sound helps them to detect prey underwater. It has been suggested that seals echo-locate, like whales and bats. Common seals are known to make clicks and trills underwater. It could be, however, that they are simply talking to each other.
Touch: when water is especially dark or murky, seals cannot use their excellent eyesight to help catch their prey. They have, however, sensitive whiskers called ‘vibrissae’ that grow on either side of the snout, above the eyes, and on top of the nose and are thought to detect vibrations in the water caused by moving prey. There are cases of blind seals surviving for a number of years in the wild, suggesting that for fishing the whiskers are more important than sight.
Smell: a sense of smell does not work in water for seals. If you watch a seal, you will see that it closes its nostrils tightly before diving, to prevent seawater from irritating the delicate membranes in the nose. But the nose-bones in the seal are large and quite complex, suggesting that a sense of smell is important on land. As soon as a pup is born, it and its mother sniff at each other. Not only do they recognise each other by their individual call, but by their individual smell. Basking seals often raise their heads and sniff at the air.
God's perfect design for the large brown eyes of the finfoot is to enable them to see equally well in air or in water. In the air, the pupil is slit-shaped horizontally. In the water, it expands to a round shape to take in more light. Seals have little to no duct on the inside of the head to drain away tears as most mammals do. For this reason, when they are out on shore and their fur is dry, they often appear to be crying.
Hair seals have ears that are only openings in the side of their head. When the seal dives, these ears are closed partly by water pressure and partly by the seal's own muscles. Their nostrils close, too. Since sound travels so much better in water than in air, the seals can still hear, just as whales can, while their ears are closed.
Whales have no vocal cords, yet they are able to call in quite audible voices (remember the whale song clips from last week?) Seals, however, have vocal cords, and they can yelp, whimper, yap, bark, and roar. Sounds that are not vocal are often heard from seal pods. As the noisy, chubby mammals lie dozing and basking, packed together, one will hear coughs, yawns, sneezes, and more. The common harbor seal also beeps high squeaks beyond what the human ear can hear. It could be echolocation to aid them in finding the fishes, shell fishes, and crabs they feed on.
Limbs and movement
A seal has much shorter limbs than most mammals: what appear to be the armpit and groin of a seal are, in fact, the equivalent of the wrist and the ankle. By comparison, the bones of their flippers are enormously long, and the skin between them forms a web which is used like a paddle to propel the seal along. They have long, sturdy claws on their front flippers which they use to help them move on land, especially when they need to grip onto rocks or ice.
When a seal swims quickly, it holds its front flippers tightly against its sides, and propels itself with its powerful hind flippers. Its lower body moves from side to side, rather like a fish, as it moves along. When the seal is swimming slowly, the front flippers are used as stabilisers and stick out to the sides.
On land, a seal moves with a ‘hitching’ action. It forces it weight onto its chest, and then stretches its back to swing its rear end forward. The weight is transferred to the pelvis, and the chest is thrown forward. It is an inefficient way to move, and has made them vulnerable to hunting by humans. On ice, however, the seals are far more limber. Ribbon seals and leopard seals, that live in the Arctic and the Antarctic respectively, can move faster than a human can run, by flailing their hind flippers vigorously.
God has also planned for the flippers so that they do not need to be as warm as the other parts of the bodies. Little heat is lost through the flippers. Fur covers the flippers of mammals in the hair seal family. The bones of the front limbs resemble the leg and toe bones of other mammals. The long ones are inside the body, and the five rows of small bones support a wide spreading flipper complete with five toenails. When the hair seal swims, these front limbs are tucked into hollows somewhat like the human armpit, unless the creature wants to steer or to turn. Once on shore, the hair seal's front flippers take over the main work of locomotion. The hind flippers cannot be turned forward. The finny fingers are curved, stiffened, and dug into the sandy ground as the wet, slippery creature wriggles along to a spot near its fellow seals.
Regulating body temperaturesHarp seals are very good at conserving their body heat. With a thick layer of blubber under their skin, harp seals are able to hold their body heat more easily. This layer of fat also provides a means of buoyancy, stores energy, and gives the seals a shape that is better suited for the aquatic environment where they are often found. In young harp seal pups you can find fur on the surface of their skin in order to keep their small bodies warm.Another interesting way that the seals keep warm has to do with the same redirect of blood flow that allows them to remain submerged longer. They lower their heart rate by 90%; supplying only the nervous system and sense organs with a normal flow of blood. By redirecting the circulation away from the surfaces, they are preventing a substantial amount of heat loss.
Animal Corner, Seal Anatomy
Exploring Nature Seal page
General Seal Characteristics
Skin & MoltingHarp seals are well known for having a fuzzy white coat as a pup. The fur of a pup is well adapted to the lifestyle of harp seals. There is a water repellant layer on the outside to help lessen resistance in water; however there is still a warm insulating layer underneath that to help with thermoregulation. It was for this very reason that the harp seals were almost hunted to extinction. Hunters found the fur of these creatures to be very valuable.
Molting for harp seals happens once a year. During the molting period the seals get rid of their worn out skin and replace it with a new one. Most often during this time, harp seals remain on land; when replacing their skin there is a compromise to how well they can retain body heat. So as not to risk hypothermia, harp seals wait for their skin to be ready for the frigid waters of the arctic.
Most mammals drop their hair and flakes of skin all year. This dead hair and skin would be uncomfortable when water soaked while swimming. Each year, seals molt and emerge with an entirely new set of skin and hair. Seals often stay near land while the days, or the weeks, of their molt last.
The Lifecycle of the Seal
Harbor Seal Fact tabs, Alaska Dept. of Fish and Game
Photo credit: Friends of Elephants Seals
The Marine Mammal Center
Squidoo Lens on Seals
The Elephant seal, the largest finfoot of all, is a hair seal that can dive to great depths and may go down as deep as 2000 feet. The male has a trunk-like nose that develops after the male is 2 years old. It sometimes becomes long enough to overhand the mouth by as much as a foot when it is relaxed. The roar of the big elephant seal may be heard for several miles. Elephant seals eat their food without being chewed so their intestine is very long. It was noted that one elephant seal had an intestine tract 662 feet in length!
Each year in the late spring, cow and bull seals choose a stretch of beach and repel other cows and bulls trying to come ashore at that point. Seals do not appear to be sensitive to pain and will continue to fight despite deep wounds, even lost eyes. The fights can dye the surrounding beach and waters for miles, but one seal rarely kills another. Bulls do not leave the spot even to hunt for food. For 1-2 months, both cows and bulls bellow and battle.
Pups are born a week or more after a cow comes ashore, but many are crushed in the constant fights surrounding them. At birth, a pup weighs 80 lbs, is 4 ft. long, and is covered with black, wooly fur. During their first 3 weeks of being nursed, the pup may gain as much as 300 lbs, eating the rich, 4/5ths fat milk. The pups immediately lay in a blubber layer that will nourish them for as long as a month after their mothers leave them; however, many die that first year before learning how to feed themselves, as many as 50% of those who managed to survive the dangers of being born into fighting grounds.
photo credit: Exploring Nature
Walrus Mom video, National Geographic
National Geographic Walrus page
Defenders of Wildlife Walrus
Walrus printout Enchanted Learning
ThinkQuest Walrus
Heart of Wisdom links
a great Pinterest board of Arctic studies, with crafts and ideas for this weeks study
Squidoo Lens on Ocean Life with usable bits
I Choose Joy! blog has a great post on the top ten Walrus study videos at YouTube.
The walrus...a bulky, almost hairless creature, with a hide that may be as much as 2 inches thick of lumpy and bumpy skin and up to 6 inches of blubber. A heavy mustache of about four hundred stiff, white bristles, droops from the huge nose, and from the upper jaw to protect two great tusks that may weigh as much as 12 lbs each, and reach a length of 3 1/2 feet in the male, and 2 feet in the female. No flaps protect the holes that are its ears.
The walrus feeds in shallow water, digging up mussels and clams from the bottom, sorting out the empty pieces with the bristles of the mustache. The shell fishes are taken into the mouth and ground apart with the short, sharp teeth. The meat is eaten, the shells spit back into the water to sink.
Most scientists recognize two subspecies of walruses: Odobenus rosmarus rosmarus (Atlantic) and Odobenus rosmarus divergens(Pacific). Odobenus comes from the Greek: "tooth walker", and refers to the walruses' method of pulling themselves up onto the ice with their long tusks.The scientific name of the walrus means "he who walks with his teeth" and it does pull itself up onto the edges of ice floes with its tusks. It can turn its flippers forward to travel more easily on land than the hair seals. These sociable creatures like to be close to each other, and latecomers to the ice floe have no choice but to begin another layer. Sometimes the floe is overloaded at one side and will tip, dumping the whole herd back into the frigid water.
Unlike the hair seal, the walrus sleeps in the water, in an upright position. Alongside the neck are pouches the walrus can inflate at will. These hold as much as a cubic foot of air. Possibly they hold the head out of the water while the mammal slumbers.
The Encyclopedia of Earth, eared seal page
Animal Planet
SeaWorld Lesson Plans, Seals, Sea Lions, and Walrus' PDF
Another finfoot is the eared, or true, seal. They number 12 species, and like the walrus, they have massive forequarters. They swim by paddling of the front flippers. The flippers are naked, usually of black skin, with arm and leg bones projecting from the body in addition to the hand and foot bones. The rear flippers can be turned forward to support the weight of the body. The eared seals have shuffling walk and even a clumsy gallop about as fast as a man can run.
Worldwide there are 5 species of sea lion. They sport short, pointed ear flaps, the huge neck and shoulders, and the naked flippers of the eared seals. The California Sea Lion is commonly found in zoos, where it is easily tamed and taught several tricks.
The Marine Mammal Center, Sea Lions
San Diego Zoo Animal Bytes
National Geographic
In the fur seal family there are 8 species, living off the coasts of all the continents of the world except Europe. the northern or Alaskan fur seal lives along the eastern and western coasts of the North Pacific. These seals have very thick, fine fur that traps air and insulates them against the cold. Fur seals molt by shedding their hairs singly, though not all the hair is shed. Through the years to coat becomes thicker.
Every September the females and young move down the Pacific coast, swimming up to 50 miles offshore, and going as far south as California, returning to their home by June. Fur seals find it easy to become too warm out on land in the summer. They lose heat by panting and by sweating through the many sweat glands of the flippers. Sometimes they wave their black, naked fins like fans.
The sea otter, belonging to the weasel family, spends more time in the water than seals do. This creature, of the Carnivora order, eats all kinds of shell fish and other sea animals. It has the most beautiful and valuable fur in the world, with one skin bringing as much as $10,000 in the early 1900s. There are as many as 650,000 single hairs in each square inch of the pelt!
Sea otters nearly always swim on their backs, with their heads up. When the sunshine glares they shade their eyes with their paws. Shell fish, when brought up from the depths, are held and cracked open on a rock resting on their stomach. The young otter is held on the stomach, too, and fed from the milk glands. They live out from the Pacific coast in kelp beds within a mile from shore. The young are born here, and the adults sleep with strands of the kelp wrapped around themselves to prevent their drifting out into open water.
Worldwide there are 5 species of sea lion. They sport short, pointed ear flaps, the huge neck and shoulders, and the naked flippers of the eared seals. The California Sea Lion is commonly found in zoos, where it is easily tamed and taught several tricks.
The Marine Mammal Center, Sea Lions
San Diego Zoo Animal Bytes
National Geographic
Baby Sea Lion Swim lesson
California sea lions are faster than any other seal or sea lion. They can swim at
speeds up to 25 miles per hour. They can also make deep dives, staying under
water for up to 10 minutes pursuing fish, squid and shellfish.
Size Males can weigh up to 1,000 pounds and grow up to 8 feet long.
Females tend to be significantly smaller, weighing up to 400 pounds and
growing up to 6.5 feet long.
Diet A variety of fish, including Pacific whiting, market squid,
shellfish, rockfish, herring and salmon
Lifespan 18 to 25 years
Range Eastern North Pacific Ocean from the Gulf of Alaska to Baja California
Habitat California sea lions are generally found in waters over continental shelf
and slope zones; they frequent coastal areas, including bays, rivers and harbor mouths.
Predators Sea lions are hunted by orcas and large sharks; pups are hunted by
coyotes and feral dogs on land.
Relatives Sea lions and Northern fur seals are in the same family known as "eared seals."
They are known for their ability to rotate their flippers under them and "walk" on land.
Family life California sea lions do not form pair bonds; one male will breed with many females.
After an 11-month gestation period, the female gives birth to a single pup. Pups weigh 13 to 20
pounds at birth; they are usually weaned after 12 months.
In the fur seal family there are 8 species, living off the coasts of all the continents of the world except Europe. the northern or Alaskan fur seal lives along the eastern and western coasts of the North Pacific. These seals have very thick, fine fur that traps air and insulates them against the cold. Fur seals molt by shedding their hairs singly, though not all the hair is shed. Through the years to coat becomes thicker.
Every September the females and young move down the Pacific coast, swimming up to 50 miles offshore, and going as far south as California, returning to their home by June. Fur seals find it easy to become too warm out on land in the summer. They lose heat by panting and by sweating through the many sweat glands of the flippers. Sometimes they wave their black, naked fins like fans.
Kit the Sea Otter
Defenders of Wildlife, Sea Otters
The Marine Mammal Center, Sea Otters
Exploring Nature, Sea Otters
Sea otters nearly always swim on their backs, with their heads up. When the sunshine glares they shade their eyes with their paws. Shell fish, when brought up from the depths, are held and cracked open on a rock resting on their stomach. The young otter is held on the stomach, too, and fed from the milk glands. They live out from the Pacific coast in kelp beds within a mile from shore. The young are born here, and the adults sleep with strands of the kelp wrapped around themselves to prevent their drifting out into open water.
God's Amazing Sea Creatures unit, Homeschool Helper Online
lapbook, Maria's Comet, HomeschoolShare loosely tied to the mammals of the sea weeks
Squidoo Lens on marine biology topics, some good reading for these weekly studies
These mammals have all experienced the fate of the whales over the years. The walrus has always been used by Eskimos without reducing the population. Hides, tools, rope, fuel oil, and ivory were products gained from the walrus. When whales became scarce, the whalers began hunting walruses for oil until they could no longer be found in numbers large enough to be profitable. Since 1960, walrus cows and calves have been protected.
The elephant seal, being large, yielded much oil. California sea lions were also taken in great numbers for oil. The northern fur seals and the sea otter were nearly wiped out for their valuable fur. The international treaty of 1911 brought the killing to a halt, and 22 years later, a single herd of elephant seals numbering less than 100 was found.
After the treaty of 1911, no sea otters were known of, yet, in 1938 a few were discovered in a very craggy spot where hunters had failed to find the last specimens. Today they are completely protected as well.
In the treaty of 1911, nations agreed to kill only the fur seals, and only on land, where they could distinguish the cows from the bulls. The beautiful fur is now harvested annually, some 60,000 skins from bulls only. The Alaskan herd numbers 2 million.
