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Exploring the beautiful nature of California


California Nature: Pacific Harbor Seals


Pacific harbor seals are found north of the equator in both the Atlantic and Pacific Oceans. In the northeast Pacific, they range from Alaska to Baja California, Mexico. They favor near-shore coastal waters and are often seen on rocky islands, sandy beaches, mudflats, bays, and estuaries.

Pacific harbor seals have spotted coats in a variety of shades from white or silver-gray to black or dark brown. They reach five to six feet  in length and weigh up to 300 pounds. Males are slightly larger than females. They are true or crawling seals, having no external ear flaps. True seals have small flippers and must move on land by flopping along on their bellies.

In San Francisco Bay, many harbor seals are fully or partially reddish in color. This may be caused by an accumulation of trace elements such as iron or selenium in the ocean or a change in the hair follicle. The total harbor seal population in the eastern north Pacific is estimated to be 500,000, and in California the estimated population was 34,233 in 2009. They are usually found in small groups, but sometimes occur in numbers of up to 500.
California seals enjoy sunning in the California mud Early summer is a great time to travel to the coast in search of the harbor seal. California's most common marine mammal, the harbor seal is often missed at first glance. Unlike their noisy relatives, the California and Steller's sea lions and northern elephant seals, harbor seals make little noise and their mottled fur allows them to practically disappear against the rocks and sand. The key to finding the seals is knowing a little about their lifestyle.

Harbor seals spend their entire lives along the same stretch of coastline. To guard against California's cold water temperatures, seals maintain a thick layer of fat beneath their skin, giving them a thick sausage shape.

They spend many hours during low tide hauled out on a favorite sandbar or rocky island soaking in the warm sunshine. The seals tend to hunt for fish, crabs, and shellfish during high tide. Harbor seals are the most vulnerable when out of the water and will quickly swim off if you get too close.
Harbor seals give birth to one pup in the spring. In California, harbor seal pups are born between February and April and weigh about 20 to 24 pounds at birth. A pup can swim at birth and will sometimes ride on its mother's back when tired.

The dark-colored pups can be born on land or in the water, and the nursing period lasts about six weeks. After nursing is complete, the adult seals mate. Pregnancy lasts nine months, but the fertilized egg does not begin to develop for three months, aligning birth dates to the same time each year. They may live 25 to 30 years.

Pacific harbor seals spend about half their time on land and half in water. They can dive to 1,500 feet for up to 40 minutes, although their average dive lasts three to seven minutes and is typically shallow, and they sometimes sleep in the water.
Seals enjoy nature in California and in the pacific ocean Harbor seals, like all true seals, lack an external ear flap, but do have an external pinnae, or opening to the ear canal that provides them with a keen sense of hearing, responding to underwater sounds from up to 180 kHz.  In the air, hearing is reduced with a response range up to 22.5 kHz. 

Harbor seals' eyes are prominent and adapted for shades of black and white. Color vision is not necessary and therefore is probably poor to non-existent. Compared to humans, they have superior vision underwater, yet inferior on land. To protect the eyes while out of the water, mucus continually washes over them.

Since harbor seals lack a duct for draining eye fluids into the nasal passages, these fluids drip out of the eye and give the seals their characteristic wet spots surrounding the eyes. Good vision does not seem to be essential to harbor seal survival; scientists have found blind but otherwise healthy individuals, including mothers with pups, at sea.

Harbor seals have a metabolic rate higher than that of a comparable land mammal, allowing it to generate a greater amount of body heat. Heat loss is prevented by a thick layer of blubber, which not only insulates the seal, but can be metabolized for energy as well.

An additional benefit of blubber is that it provides a heat gradient from the body's core to its skin. This allows the seal's skin to be approximately the same temperature as the surrounding water while its core temperature remains approximately 100 deg F. In cold water, blood vessels constrict (contract), slowing the flow of blood to the skin and therefore, reducing heat loss to the environment. When hauled out, the process is reversed and blood vessels dilate (expand), allowing heat to be released to the environment.

Harbor seals are thought to be the least vocal of all pinnipeds, vocalizing only for defense. A harbor seals are often observed during the pre-mating and mating seasons slapping the water with their pectoral flippers as a form of communication. They may also perform this behavior to show aggression.
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