TRUE SEAL

TRUE SEAL

The true seals have no ear flaps as in comparison to the eared seals. These two families of seals exist today.

They are descended from land animals. However, it is assumed that the true seal evolved about 15 million years ago while the eared seal developed about 25 million years ago.

True seal size ranges from the ringed seal of 116-138cm till the male southern elephant seal which is 490cm. The weight of a ringed seal is 50kg and the southern elephant seal is 2500kg. Amazingly, the females of southern species which are monk, leopard and Weddell seals are larger than the male.

In contrast, the males of the northern species like the grey, hooded and elephant seals, are much larger than the females. The different sizes between the male and female are enormous with the southern elephant seal; the male is three times the weight of the female.

ELEPHANT SEAL 
FEMALE AND MALE

RINGED SEAL

RINGED SEAL PUP

WEDDELL SEAL

HABITAT

The habitat of seals, because they are sea mammals, they spend most of their time in the ocean. They come on land to breed and rest.

Weddell, crabeater, leopard, southern elephant and Ross seals live amongst the ice floes of the Antarctic waters. The harp, bearded, spotted, hooded and ringed seals are amongst the arctic pack ice.

Ringed seal live under the Arctic ice almost all year round and scraping breathing holes, near pressure ridges, in the ice. Under the deep snow they excavate ice caves to haul out or rest. It is assumed that the males defend their territory under water. The Weddell seals do it too. When the spring sunshine begins to melt the ice, the ring seals congregate on the surface. After the ice melted they go back to sea for the short summer.

The Harbour seals live further south and closer to man. They often rest on a sandbank or bay. The grey seals are more oceans going but does come out and lies on a rock to dry its pelt.

It is thought that the first seal probable evolved in warm waters. However, the monk seals are living in sub-tropical waters but their numbers are declining.

The Baikal seal is the only freshwater species and it lives in the Lake Baikal in Siberia.

HEAT CONSERVATION

The seal blood has to be kept at 37C to survive the cold sea water. They live in Arctic and Antarctic in water temperature of -1.8oC. To avoid heat loss the seals are cylindrically built. The seal has a layer of blubber of 7-10cm all over the body. This fatty tissue protects and streamlines the body.

SWIMMING

The true seal swings its tail from side to side in opposition to the powerful strokes of the hind flipper. The fore flippers they keep closely to their sides.

On land the true seal can move a short distance with humping their way over the ground. The Grey seal uses its flippers to haul them onto the rocks. The ribbon and crabeater seal travels over ice by wriggling.

DIVING

Being descended from land mammals, the seals have lungs and have to hold its breath when diving. The seal has more ribs and the lungs are larger than most land mammals. The lungs don't carry air when they dive. They breath quickly to fill their blood with oxygen and just before diving they breath out to get the air our of their lungs.

The harbour and harp seal dive for about five minutes but if necessary they can stay under water up to half an hour. Larger seal can stay under water longer. The northern elephant seal can dive up to 47.7 minutes and the Weddell seal up to 73 minutes.

The Weddell seals can dive up to 600m. When they do this the blood circulation to the heart, brains and lungs is slowed down. The heart rate drops from 50-60 beats per minute to 15 beats. After such a lengthy dive the seal will rest an hour and half to recover.

FOOD

Their food consists of fish, planktonic crustacean and molluscs. They switch from one food to another whatever is available. The Weddell seal in the Antarctic Peninsular eats octopus and squid but in the Ross Sea they eat fish. Grey seals living near salmon fishing stations on Great Britain's northwest coast feed on salmon. When they are in other areas they ignored the salmon.

The crabeater seal does not eat crabs but live on krill and some kind of zooplankton. The crabeater seals are eaten by the leopard seal which also catches penguins.

Seal stay without food for a long time when breeding and moulting. The weaned elephant seal does not eat for 12 weeks while learning how to hunt.

BREEDING

At mating season only the dominant male covers as many as females as possible. But as there are other males the dominant male must lead an aggressive live. The female gives birth and nurture her single offspring. The breeding season varies. The female gives birth at the same time every year and mates shortly after giving birth. They have a delayed implantation of the foetus and the females give birth on the communal breeding beaches every year. The male does not help to raise the pup and comes purely for the mating season to the beaches.

There is a great variety of giving birth at which place amongst the seals. Some on ice, others on beaches or water. True seals leave their pups on the beach and return to the sea and going back only to feed them. However, the harbour seal has a very strong bond with the mother. The pup cannot stay under the water or swim very far. The mother carries it on her back or holds it between her flippers. When there is danger she makes a loudcrack on the water to make her pup dive.

The elephant seal differ so much in size, between the female and the male; you would think they are different species. The female has a sleek body and looks rather underdeveloped; the male is huge and has three times the weight and size of the female. The male neck and chest is covered with thick wrinkled skin. The huge head has an elephantine nose.

Male elephant seals fight violently about their territory. They are also very aggressive toward the female. They rape pregnant females as well as the ones which just have given birth. When she resists, they bite the female or slam it with their huge body. They also squash pups to death.

The ringed seals mates under the ice and the female gives birth in the early months of the year inside a maternity cave which was dug out in the snow.

FIGHT FOR SURVIVAL

The relationship between man and seals are complex. They find them fascinating enough to put them into folklore and legend yet they hunt them to almost extinction. The reason is they get blamed for depleting fish-stock. The other is for their fur.  In the 1970 harbour seals and grey seals were seriously in trouble in northern British waters. They hunted nearly all the pups. Harbour seals were shot trying to protect their pups.

Fur trade worked by supply and demand and when the demand stopped, the killing ceased. Then they could also enforce protective legislation. It is thought that today are more seals around than for the last thousand years.

There was an outcry when they showed a film on the TV showing a pup being clubbed in front of his mother. However, it is still going on today. The culling of harp seals in Greenland and Newfoundland is controlled by an agreement from Denmark, Norway and Russia. The population is now on the increase. Unfortunately, because of their beautiful belts and Norway trying to protect the capelin fisheries, the culling will continue in spite of the outcry.

The ring seals are not better off because their population were reduced from many hundred of thousands down to 10,000 in the Canadian Arctic. In the Baltic Sea they are affected by chemicals being damped into the sea. The chemical waste was of organ chlorines called polychlorinated biphenyls (PCBs) These chemicals also had an affect on the seabirds around the British Isles.

The warm water monk seal is the rarest seal of them all. It is thought that the Caribbean monk seals are extinct. The last time it was sighted was in 1950. Furthermore, the HawaiianTop of Form

 Mediterranean monk seal are in danger of being extinct. One reason for it was hunting and the other monk seals are very sensitive and react badly for being disturbed.  If pregnant females have to give birth on an unsafe beach and then being disturbed the pups could starve to death. Every effort is made to safe the Hawaiian monk seal but in spite of all the number remain small.  As for Mediterranean monk seal it has lost its sites mostly to developers.

EARED SEAL

EARED SEAL

When you look at seals they look all the same at first glance. However, if you look closer there are two different groups. One of the groups has retained a distinct, protruding ears hence the name 'Eared Seals' the other group has not.

Of course, all seals have ears but ears of the so called true seal are reduced to small openings which, it is assumed, make them more streamlined.

This minor point comes from a complete separate evolution. The true seal is thought to have evolved from otter-like creatures in the North Atlantic, about 15 million years ago. The eared seal evolved from dog-like creatures in the North Pacific about 25 million years ago. From this evolution they have a dog-like look, a very great mobility on land which in comparison the true seals is almost helpless on land.

TRUE SEAL COLONY

On land the true seal lies on its stomach with the front flippers stretch out on either side. The hind flippers trailing on the ground and to move forward it humps its body along.

On the other hand the eared seal stands on all four of its limbs. The front flippers are equipped with powerful muscles that bear the animal's weight. The hind limbs are turned forward under the body instead of trailing behind. When it moves slowly it waddles on the heels. The tips of the flippers are held upward from the ground. When it feels danger, it speeds up and throws both front flippers forward - like a man on crutches.  It looks clumsy but it can move fast and outrun a man.

Again the swimming techniques are quite different. The true seal uses its hind flippers and with powerful strokes propels itself through the water. The eared seal zooms through the water with using his front flippers and the hind flippers are only used like rudders. Therefore, all the muscle-power comes from the shoulder and neck. Through these exercises it keeps the muscles strong to use them on land.

Like all seals it spends its life in water and through evolution it became an efficient swimmer. The streamlined body gives an effortless efficiency in water. In spite of the sleek body of the seal it has a small face preventing heat loss. The thick fat layer under the skin gives not only insulation but also a further streamlining.

ANTARCTIC FUR SEAL

The fur seal has a tense woolly undercoat with longer and coarser guard hair on top for further protection 
he two types of hairs couple and is extremely protective against water reaches the skin, preventing heat loss.

However, during a deep sea dive the insulation of the fur become less because the warm in the fur will be compressed by water pressure. Despite of this the Cape fur seal dives often to a depth of up to 100m. Californian sea lion have been trained to dive even deeper. The eared seal are not such great diver. The reason is that they can't or won't hold their breath for long periods. The true seal can stay under water for 20 minutes. It empties its lungs stores the high concentrated oxygen in its blood. Eared seal do not have this capability and only stay under water for about five minutes.

When on land the fur seal is very clumsy but in water it is like a torpedo and with intelligence plus resourcefulness of a wolf. They are predators but some are better than others. in the group of eared seals, the fur seal feeds almost entirely on krill. These shrimp-like creatures are in their millions in the Polar seas. They are the diet of the great whale but them almost extinct in the Southern Ocean and it is thought that this may have resulted of a population explosion of the Arctic fur seal.

On a whole fur seal and sea lions kill and eat anything they get hold of. They live in a region of whirling ocean currents bringing up nutrient-rich water from the seabed near the coast. These nutrients then nourish the microscopic algae floating in the sun on the surface of the water. This will provide food for the tiny floating animals. Great shoals of fish will be attracted which then feed the seals.

Eared seal hunts in the middle of the water and on seabeds. It feeds on fish, squid and sometimes on penguins. as well as crabs and crayfish which are at the bottom of the sea.

On the beach it can see fairly well in bright sunshine but not much when the light is fading.  In the sea it can see everything in sharp focus even when the light is almost zero. The seal doesn't depend on eyesight. It had been noticed that a totally blind eared seal is well fed in the wild. It proves that other senses are used to find food.

The ears are developed to cope with the greater pressure of sound waves in water. It also is capable to take the increasing pressure as it dives, through a special mechanism. The hearing is remarkable in pinpointing the sounds of its prey and it can home in on it in dark, cloudy water.

Through its cat-like whiskers it picks up vibration in the water. Each whisker has a complex network of nerve fibres which sends messages to the brain. This gives it the ability to track its prey in total darkness.

The fur seal and sea lions breed in tightly packed colonies and give birth. They rear their babies and mate again before they return to the sea at the end of the season. They developed this colonial habit because of the shortage of beaches. The other reason is that they are vulnerable to predators.  Although the eared seal is quite mobile it still gathers together into groups and the female comes to the beach to give birth.

They mate soon after the female gave birth. The male arrives at their breeding ground first. When the female emerges out of the water it has to move into his territory. This gives the male an opportunity to have a harem of up to 50 females. It leaves a lot of other males or bulls without any female. There is a lot of fighting going on and some are so serious insured, it leads to death even with their thick hide.

SEA LION AND HIS HAREM

When a bull claimed a territory he has to stay there right through the mating season and live on his fat reserves. If he doesn't, he looses his place. The females arrive two to three weeks after the bulls claimed his place. The pregnant females first. The seals have delayed development of the foetus. This enables the female to give birth exactly one year later. The female stays with its pup for six days then she wanders about and goes back to sea. The male will mate with her when she starts to wander around. She goes to sea hunting and returns to the pups to suckle them for at least 100 days.

SEAL PUP

A number of species suckle their pups for a year and when she returns to the beach to give birth; it is not unusually she is accompanied by her year old pup.

The secluded breeding beaches provide protection from predators but not from man. When they discovered in 1786 the huge colonies of northern fur seals on the Alaskan Pribil of Islands; the sealers wiped them out. The same happened on South Georgia with the Antarctic fur seals in the 19th century.

It was their skin with their beautiful woolly undercoat which the sealers were after and they didn't do a great selection amongst the animals. They slaughtered any seal that came on land, including pregnant females. It wasn't surprisingly that by 1910 the Antarctic fur seal was practically extinct and the other species were not far off.

It was just in time when the hunting restriction came into power during the early 20th century otherwise the seals would have disappeared. Only through sheer conservation the population has increased, especially the Antarctic fur seal. Due to this timely intervention the eared seals are thriving again. However, the large mammals round the world do not do so well.

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