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Adaptations
Flippers
Pinnipeds have shorter limbs than most other mammals. As noted above, their limbs have evolved into flippers with true seals having more developed hind flippers and eared seals having more developed fore flippers. The walrus is intermediate between the two. A pinniped’s fingers and toes are bound together by a web of skin . They also have claws are can either be in the on the front flippers (earless seals) or back flippers (eared seals). Pinnipeds can move weightlessly in the water and thus their flippers can be smaller in relation to their size than the wings of a bird or bat.

Oxygen conservation
Pinnipeds can conserve oxygen for long period of time underwater. When the animal starts diving its heart rate slows to about one-tenth of the norm. The arteries squeeze shut and the sense organs and nervous system are the only organs to continue to receive a normal flow of blood. Pinnipeds are able to resist more pain and fatigue caused by lactic acid accumulation than other mammals. However once they return to the water surface, they need time to recover and bring their body chemistry back to normal

Warmth
To keep warm in cold waters, pinnipeds have a layer of blubber under their skin (which also provides buoyancy). The thickness depends on the species. Their blubber can also provide food for the animal. Newborn pinnipeds have no blubber.

Some pinnipeds can also can get warm from their fur. The white coat of the infant harp seal, may trap the energy of sunlight as heat near the skin. As noted above, fur seal have underfur.

Moulting
Like other mammals, pinnipeds have to shed their fur once in a while. Eared seals shed more slowly than earless seals. Most earless seals spend time in the water while moulting.

Other adaptations
A pinniped’s eyes are well adapted for seeing both above and below the water. When diving the animal has a clear membrane that covers and protects its eyes. In addition, its nostrils close automatically. Testicles and mammary glands are located in slits under the skin to keep the pinniped’s streamlined shape. They also have whiskers to help navigate and sensors in their skull to absorb sounds underwater and trasmit them to the cochlea
 

SWIMMING

1. Harbor seals swim with all four flippers: they move their hind flippers from side to side to propel themselves forward, and use their foreflippers to help them steer.


2. Harbor seals can swim forward and upside-down. They rarely swim backward.

3. Harbor seals can swim up to 19 kph (12 mph), but they generally cruise at slower speeds.

DIVING

1. Harbor seals can dive to depths exceeding 200 m (656 ft.). They don't routinely dive this deep, however, since most of their food is found in shallow waters.


2. Adult harbor seals can stay submerged for up to 30 minutes, but dives usually last only about three minutes. A two-day-old harbor seal pup can stay submerged for up to two minutes.


3. All marine mammals have special physiological adaptations for diving. These adaptations enable a harbor seal to conserve oxygen while it is under water.

• As with other marine mammals, when a harbor seal dives, its heart rate slows - from 75 to 120 beats per minute to only four to six beats per minute. When a seal surfaces after a long dive, it experiences an accelerated heart rate for a short time.

• When diving, blood is shunted away from tissues that are tolerant of low oxygen levels to the heart, lungs, and brain, where oxygen is needed.

• A harbor seal has a greater volume of blood than a land mammal of similar size; therefore, it can retain more oxygen.
• The muscle of harbor seals also has a high content of the oxygen-binding protein myoglobin (about 10 times as much as humans). Myoglobin stores oxygen and helps prevent muscle oxygen deficiency.


4. Before a deep dive, a harbor seal exhales to reduce the amount of air in its lungs. Oxygen is stored in the blood and muscle tissues, rather than in the lungs.


RESPIRATION

1. Like most other marine mammals, a harbor seal's typical respiration cycle is a short exhalation, a short inhalation, and a longer breath-holding (apnea) period.


SLEEP


1. Harbor seals sleep on land or in the water. In the water they sleep at the surface and often assume a posture known as bottling - their entire bodies remain submerged with just their heads exposed. This enables them to breathe when necessary.

THERMOREGULATION


1. A harbor seal's core temperature is about 37.8ºC (100ºF). There is a heat gradient throughout the blubber from the body core to the skin. The skin remains about one degree Celsius warmer than surrounding water.

2. Harbor seals have a metabolic rate somewhat higher than land mammals of the same size. This helps them generate body heat for warmth.

3. A thick layer of blubber insulates the harbor seal, reducing heat loss. The blubber of a northern Pacific harbor seal during winter may account for 27% to 30% of its total body mass. Blubber also streamlines the body and functions as an energy reserve from which the harbor seal can draw energy during periods of fasting. A harbor seal's hair provides no insulation.

4. In cold water, blood is shunted inward as blood vessels in the skin constrict, reducing heat loss to the environment.

5. When hauled out on land, blood vessels in the skin dilate, allowing heat to be released to the environment.

6. To prevent heat from escaping through the flippers, seals hold them close to their body.


content provided by "http://www.seaworld.org/animal-info/info-books/harbor-seal/adaptations.htm" for informational purposes.
 
Facts About Seal
With their big, brown eyes and appealing dog-like faces, seals are attractive creatures. They live all over the world, from the frozen wastes of the polar regions, to the tropical beaches in Hawaii, and almost everywhere in between. Like dogs, cats, whales, mice and humans, seals are mammals – which means that they are warm-blooded and suckle their young. Millions of years ago, the ancestors of seals moved from the land back into the sea and evolved special characteristics to adapt to their environment.
 
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