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Sea lion

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Sea lion
Sea lion 2.jpg
Scientific Classification
Genera
  • Arctocephalus
  • Callorhinus
  • Eumetopias
  • Neophoca
  • Otaria
  • Phocarctos
  • Zalophus[1]
Sea lion 3.jpg
A California Sea Lion takes a rest for a moment after a hard day's work

Sea lions are any of the species of seals belonging to the taxonomic family Otariidae. There are about fourteen species, and are also known as the eared seals or fur seals. [2] Sea lions can be found in almost every ocean in the world, with the exception of the Atlantic Ocean, though they are hardly ever seen in the Arctic Ocean. [3] Sea lions have a strong sense of community and often collect in "Harems," a group of up to forty females led by one male.[4] They are carnivorous mammals with four fins, (known as pinnipeds).[5] They dine on many different types of sea creatures, including herring, rockfish, and mackerel, salmon, pollock, flounder, anchovies, Pacific cod, capelin, squid, octopus, and even clams. [6] Sea lions are preyed upon by orcas, sharks, and humans. The water dwelling creatures are born with a full coat of fur and open eyes, and can move after a half hour. Pups stay with their mothers for about one year before moving on and making their own family, with females reaching maturity by four years of age, and males reaching it by six years. At eight years both male and female have officially reached their adult years, and they have a lifespan of up to 30 years of age.[4]

Body Design

A California Sea Lion shows off it's thick and warm layer of outer fur.

Members of the family Otariidae possess similar design characteristics with the seal and walrus. This is because they are all Pinnipeds, meat-eating mammals found in aquatic habitats that use flippers resembling fins for locomotion. [7] Otariids can be distinguished from their relatives by pinnae (external earflaps) and use both their hind and fore flippers to waddle around on land. Otariids have been observed to “glide” or almost “fly” through the water by swimming with just their fore flippers. Phocids (True Seals), are a similar family to Otariidae, but don’t contain external earflaps or use their hind flippers to move across the earth. They also only use their hind flippers to launch themselves through the water[8] (also called pectoral oscillation in the scientific community).[9] The characteristics attributed to this type of swimming are mainly shortened limb bones that are completely encased within the Sea Lion's body which increases the speed in the water. This type of design is ideal for the reduction of drag and improved streamlining (offers the least resistance to fluid flow)[10] Otariids also have a flattened body shap from the back to the belly, also known as "Dorsoventral."[11] The fins of a sea lion have a wing-like appearance to them, which attach to the large body that decreases to a relatively small pelvic girdle.

True to their name, fur seals contain an insulated layer of fur that encases air bubbles to help the animal stay warm in frigid waters. This short, compressed covering of fur is covered by a longer, less dense coat. No matter how much time fur seals spend diving into the ocean, they will always feel dry due to the genius of this design. Dissimilarly, sea lions only has a layer of scattered, shorter hair that is not able to keep the animal dry. Both sea lions and fur seals contain a thick pad of blubber between the skin and muscle layers.[12]

Males, a rich, chocolate brown, differ in appearance from the females of their species in many ways. Females often have a lighter appearance, due to the golden tint of their brown fur. Male sea lions, much like humans, are prone to a lightening of hair on top their heads. Some of the very elderly male sea lions have nearly a pure white patch of fur! Females are also towered over by their male counterparts. Males, also known as bulls, are immense compared to the females, weighing anywhere from 600 to 850 pounds, sometimes even up to 1,000 pounds. They can reach seven feet in length. The rather petite females weigh only 220 pounds and can have a length up to six feet. By the time they reach five years of age, the bulls develop a bony bump on top of their skull called a sagittal crest.[13]

Life Cycle

Sea lions give live birth. The scientific term for carrying young internally and having no egg structure at any point during development is viviparous.[14] After a gestation period of nine to 11 months, the mother sea lion gives birth to a fully furred pup emerges with open eyes. The baby is quickly able to move about in half an hour. The mothers, also called cows,[15] fast and stay with their young for up to seven days before venturing out to the ocean for a replenishment of food and nutrients. While the mothers are absent, the pups congregate to play and enjoy themselves.

Pups and their mothers have a special way of identifying each other. In a group of hundreds of sea lions, (which all look the same to a human's eye), the cow is able to pick out their pup by its distinct scent and call. Though at three months the baby sea lion is able to digest fish, it stays and nurses from its mother for another year. Gradually as they get older, the pups venture out into the deep ocean under the watchful eyes of their mothers. After a year passes, the pups leave their mothers and live independently; ready to mate and start their own family.

Early August to December is the mating season for sea lions. When this time of year comes around, male sea lions begin to show an intense interest in the females belonging to their harems(a group of up to forty females led by a bull).[4] Males become very vocal in both defending their territory and flirting with the females. Other mating behavior includes: touching the females with their snout and mouth, smelling, and biting the female playfully. Females are prevented from leaving the beaches until they have mated.

The mortality rate for baby sea lions varies greatly with the size of the population, so it can range from two to fifty percent. In larger populations, there is a higher pup mortality due to a greater risk of pups being trampled to death by adult sea lions, such as during raids. Male sea lions occasionally organize raids and abductions of pups to attract mothers away from their territory for mating purposes, which may also signify strength and power.

Sea lions reach their maximum size around 8 years of age, but maturity is reached at different times depending on the gender. Male pups reach maturity at 6 years of age, whereas females mature at 4 years. Depending on living conditions, sea lions can live up to 30 years of age. Death can be caused by predators, (such as whales or sharks),[4] diseases, parasites, drowning, abduction by males, trampling to death, and starvation (if they lose their mothers).[16]

Ecology

A mother Sea Lion protects the multiple pups in her charge.

Ecology is the science of the relationships between organisms and their interactions with their natural or developed environment. [17] The carnivorous sea lion feeds on a variety of different species. The majority of their food comes from the ocean. Though it depends on where the sea lion is from, most of their diet includes but is not limited to herring, rockfish, and mackerel, salmon, pollock, flounder, anchovies, Pacific cod and capelin. Sea lions also enjoy indulging on squid, octopus, and even clams. In just one day, sea lions can ingest five to eight percent of their body weight, which is about fifteen to thirty-five pounds! [18] Though considered fearsome predators, sea lions are also preyed upon by Great White sharks, killer whales, and humans.

Sea Lions can surprisingly be found in many different areas of the world, with the major exception being the Atlantic Ocean. Uncommonly, certain sea lions can choose the Arctic Ocean as their habitat as well. They are generally found in shallow waters and coastal areas where food is abundant. The fourteen species of sea lions can be found in both the northern and southern hemispheres, and both sub arctic and tropical waters. The most common species, the California sea lion, can be found anywhere along the coast of California and Mexico. South American sea lions choose southern Brazil to Chile and Peru as their ecological niche. The Australian sea lion and the New Zealand sea lion are each located in the areas they were named after. [19]

Learned Behavior

Many people have memories of attending a sea lion show at a circus or an amusement park, enjoying the impressive tricks the aquatic mammals eagerly completed for a reward of a piece of fish or another tasty morsel. The sea lion they were most likely watching was a California Sea Lion, known by the species name Zalophus californianus [20]Performing tricks for the amusement of humans is an example of learned behavior, which is simply behavior that must be taught instead of knowing instinctively. Learned behavior is essential for members of the family Otariidae to survive. From nearly the moment a sea lion pup is born, it must start learning from its parents to one day be able to survive independently. Its parents immediately start teaching the pup how to catch its food and what is safe or harmful to eat. The parents also let the pup know what sort of animals to stay clear of in the ocean. Just like innate behaviors (reflexes and instincts), [21] sea lions can remember learned behaviors for the entirety of its life. [22]

Gallery

References

  1. Otariidae. Otariidae Taxonavigation. Web. Gray, J. E. Date Accessed: 30 January 2012
  2. Taxon: Family Otariidae . The Taxinomicon. Web. Unknown Author. Date Accessed: 17 January 2012
  3. Where Do Sea Lions Live. Wiki Answers. Web. Unknown Author. Date Accessed: 30 January 2012
  4. 4.0 4.1 4.2 4.3 California Sea Lion Zalophus californianus. Denver Zoo. Web. Unknown Author. Date Accessed: 30 January 2012
  5. Pinnipeds. The Free Dictionary. Web. Unknown Author. Date Accessed: 17 January 2012
  6. What Do Sea Lions Eat. Want To Know It. Web. Unknown Author. Date Accessed: 30 January 2012
  7. Pinnipeds. The Free Dictionary. Web. Unknown Author. Date Accessed: 17 January 2012
  8. Lions of the Gulf of the Farallones. “Farallones.” Web. Unknown Author. Date Accessed: 17 January 2012
  9. Walker's Marine Mammals of the World. "Google Books". Web. Nowak, Ronald. Date Accessed: 17 January 2012
  10. Streamling. The Free Dictionary. Web. Unknown Author. Date Accessed: 17 January 2012
  11. Walker's Marine Mammals of the World. "Google Books". Web. Nowak, Ronald. Date Accessed: 17 January 2012
  12. Blubber. The Free Dictionary. Web. Unknown Author. Date Accessed: 17 January 2012
  13. California Sea Lion. The marine mammal Center. Web. Unknown Author. Date Accessed: 30 January 2012
  14. Babies and Birth – Eggs or Live?. Double "D" Reptiles. Web. Unknown Author. Date Accessed: 30 January 2012
  15. Sea Lion. Arlington Heights School District . Web. Alexandra. Date Accessed: 30 January 2012
  16. Otaria flavescens. Animal Diversity Web. Web. Unknown Author. Date Accessed: 30 January 2012
  17. Ecology. The Free Dictionary. Web. Unknown Author. Date Accessed: 30 January 2012
  18. What Do Sea Lions Eat. Want To Know It. Web. Unknown Author. Date Accessed: 30 January 2012
  19. Where Do Sea Lions Live. Wiki Answers. Web. Unknown Author. Date Accessed: 30 January 2012
  20. Fishin' for Facts: California sea lion. Whale Times. Web. Musgrave, Ruth A. Date Accessed: 17 January 2012
  21. Mealworm Behavior. Virtual Lab. Web. Unknown Author. Date Accessed: 17 January 2012
  22. Fishin' for Facts: California Sea Lion. Whale Times. Web. Musgrave, Ruth A. Date Accessed: 17 January 2012