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    Harbor Seals Essay (1636 words)

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    Harbor seals are marine mammals that have spotted coats in a variety of shades from silver gray, black to dark brown. They reach 5 to 6 feet in length and weigh up to 300 pounds. Harbor seals are dimorphic, with the male being slightly larger than the female. They are true, or crawling seals, which means they have no external earflaps. True seals also have small flippers, and move on land by flopping along on their bellies.

    They breathe at the surface and hold their breath while diving. They can dive to 1,500 feet for up to 40 minutes, although their average dive lasts 3 to 7 minutes. Their scientific name basically means sea calf or sea dog. This nickname is fits them well, as these seals closely resemble a dog when their head is viewed at the surface of the water. When the harbor seal pup (baby seal) is born, it has a coat that closely resembles the adult coat. Some have a longer, softer white or gray coat (lanugo) when born, but they shed that coat within about 10 days.

    Harbor seals are found across the Northern Hemisphere in both the Atlantic and Pacific Oceans. In the northeast Pacific, they range from Alaska to Baja California, in Mexico. They live near-shore coastal waters and frequent sandy beaches, mudflats, bays, and estuaries. Some harbor seals even live in certain areas of Europe such as Finland. The total harbor seal population in the northeast Pacific is estimated to be 330,000, in California the estimated population was 40,000, and in Europe the estimated population was 6,000 in 1997.

    Harbor seals spend about half their time on land and half in water, and they sometimes sleep in water. They may sleep most of the day on the beach to keep safe from the predators that hunt them, and go into the water only a couple of times each day to hunt for food. Harbor seals dont have a permanent place to live but they usually are found in small groups, but sometimes occur in numbers of up to 100 to 500. Their average life span is around 25 years, although some have lived for over 30 years. However, males seem to live shorter lives, probably because of the added physical stress of fighting during mating season. The Harbor Seal is both a predator and a prey.

    They are very vital in the food chain. Seals eat a lot of fish and prevent over population, and they are a great source of food to animals such as orca whales, great white sharks, polar bears, eagles, seal lions, and sometimes even coyotes which prey on pups. Wild harbor seals probably consume 6 to 8 percent of their body weight in food per day, depending on the nutritional value of the food being eaten. Their diet varies greatly depending on location. The seals tend to hunt for fish, crabs, shellfish, octopus, squids, crustaceans, and mollusks.

    They are excellent hunters and can prey very well. They generally feed close to shore or in shallow waters, and have been observed feeding during both the day and night. The seals have a keen sense of smell and have great eyesight, and use these senses to find its food remotely easily. Location plays a key factor for mating season also, but usually begins in late November and peaks in the first half of May.

    The pups are usually born around springtime. Harbor seals only mate in water, but give birth on land or in the water. Female harbor seals can give birth when they are 3 to 5 years old. Harbor seals give live birth to a single pup that is usually around 2 and feet long that weights around 15 to 20 pounds.

    Gestation usually takes place in 9 months, but the egg doesnt get fertilized for 3 months, making birth dates around the same time each year. The pup usually rides on its mothers back for the first week of its life, and unlike many other seals, they are able to swim at birth. The pup nurses on its mothers fatty milk for the first 4 weeks of its life, which almost doubles the pups weight by the time its weaned. After about four weeks, the pup is weaned and is left to go on its own. Harbor seals belong to the scientific order Pinnipedia, which includes seals, sea lions, and walruses.

    Seals differ from sea lions in a number of ways, including having shorter, stouter flippers, and no visible ear flaps. The harbor seal is not on the endangered list, but is protected under the Marine Mammal Protection Act of 1972. It is unlawful to feed, touch, or harass these animals. These seals are the most common marine mammals in areas such as California, which definitely doesnt make them endangered. Like most animals, the harbor seal is very unique.

    Unlike other sea animals such as walruses and sea lions, harbor seals rarely interact with each other and remain solitary. When hauled out theres as much as 3 feet or more in between each seal. Harbor seals are very uncommunicative, and often respond to each other by snorting, growling, lunging, scratching, and other aggressive gestures. The harbor seal also has live births that could swim instantly, unlike most other marine animals. If a harbor seal feels threatened or is under attack, most likely it will use its only useful defense, which is to swim away immediately. Since the seals predators are much larger than the seal itself, it would be useless to put up a fight in order to get away.

    If a human disturbs a pup too often and leaves a sent, the mother seal will abandon her young. Harbor seals, like most other seal species, migrate southward every winter, returning to New England and Canada in the summer. On Long Island a large group of these seals come in November and remain through mid May, although some are known to stay throughout the whole year. Migrating southward every year became a natural instinct after thousands and thousands of years.

    Harbor seals have been hunted for food, fur, and lantern oil by people for hundreds, probably thousands, of years. Humans have some sort of an effect on the seal. Air pollution changed the color of the harbor seals coat in parts in California. Iron oxide precipitates deposited on the hair of the seal changes the coat color to a reddish color.

    In the late 1980s, a virus killed thousands of harbor seals in the waters around northern Europe. Because of their presence to human activities in Europe and parts of North America, the bodies of harbor seals often contain high concentrations of chemical substances such as heavy metals, PCBs, and DDT. Also disturbance caused by humans can have a major effect on haul numbers; chronic disturbance may lead to the abandonment of a haul out site. Harbor seals rarely communicate and use a short gesture to communicate with each other. Different gestures express different moods of the seal. The seal can feel threatened and snort or growl.

    Most of the time the harbor seal is considered to be a very quiet animal. The most talking between the harbor seals would be between the mother and pup. Pups make a noise that sounds like “maaaa” or mom. Harbor seals live both independently and in groups. It depends on the seal itself, whether it gets along with the group or not.

    Most of the time though harbor seals will be found in large groups ranging from 100 to 500. These seals dont really compete over anything; they have no reason to. There is in some areas a potential for competition with the grey seal. If they do compete over food, and there is danger, the mother would be very protective to her young. While taking care for their young, harbor seal mothers are very protective and will sometimes push the pup beneath the surface or carry it on her shoulders to avoid danger. This animal serves an important purpose in the biosphere, which relates to the food chain.

    Without the harbor seal, there might not be enough food to feed all of the orca whales or the great white sharks. Also, the fish population might be unbalanced and there would be too many fish to support. Over the thousands of years the harbor seal has been on earth, it changed to adapt to its environment. There was a reduction of external appendages on the harbor seal’s body, which was to reduce drag when they are swimming. All four limbs on the body are now modifiable. The flippers are long, flattened and fully webbed.

    Harbor seals adapted to diving, too. When the harbor seal dives, the heart beat decreases, the metabolic rate decreases, and the body temperature decreases. They have a high tolerance to carbon dioxide in the tissues, they have the ability to store large amounts of oxygen in the muscle tissues, and they have the ability to make their lungs collapse when air is expelled before they dive, which helps to prevent the bends. To help see in dark and murky waters, the seals have special adapted eyes that make them able to see in such conditions.

    To guard against very cold water temperatures, harbor seals maintain a thick layer of fat beneath their skin, giving them a thick sausage shape. To make the harbor seals less noticeable to predators, their coats sometimes blend in with the rocks or sand theyre lying in. To help them find food easier, they have a keen sense of smell. Without these adaptations, who knows if the Harbor Seal would still exist today. *Hanan, D.

    (1999). Pacific Harbor Seals. Alolkoy Publishing Co. PP 12-59. *King, J. (1983).

    Seals of the World. British Museum (Natural History) and Cornell University Press. PP 20-26.*Internet: Sea World web April 20, 2001*Internet: The Marine Mammal Center web April 20, 2001Words/ Pages : 1,637 / 24

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