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.