Chapter 3: Pinnipeds and other Marine Mammals

 

Common or Harbor Seal

a harbor seal (this image from the Wikimedia Commons)

Pinniped Classification

Pinnipeds are divided into three main families: Phocidea (the true seals), Otaridae (sea lions and fur seals,) and Obodenidae (walruses.)

hooded deal pup

Family Phocidea - True Seals

True seals, also sometimes know as earless seals include a variety of species that are distinctive from sea lions.  Seals have no external ears, they can't walk on land, and most breed and have their pups on sea ice.   Seals swim with a waggle of their hind flippers and lower torso. Most seals have thier pups on sea ice and wean their pups very quickly. Seals eat a variety of foods, but the bulk of most seal's diet is fish.  

Austrialian Sea Lion

an Austrailian Sea Lion (this image from the Wikimedia Commons)

Family Otaridae (Sea Lions and Fur Seals)

Sea lions have distinctive external ears.  They can fold their back flippers forward and walk on their hind flippers.  Sea lions swim by flapping their front fillers like wings. Sea lions (along with fur seals and elephant seals have distinctive sexual dimorphism (males are much larger than females) and polygynous breeding that occurs on land.

Walrus

a walrus (this image from the Wikimedia Commons)

Family Odobenidae - Walruses

The walrus has a mixture of qualities from both the true seals and sea lions.  Like true seals, walruses do not have an external ear.  Similar to sea lions, they can move their hind flippers forward and underneath their bodies but they cannot bear weight.  Both male and female walruses have tusks (large canine teeth.) Male tusks are slightly larger than females and can reach almost a meter in length. Walrus's have thick, well insulated skin that lacks the visible hair or fur of the other seals. Walruses are one of the largest pinnipeds (only male elephant seals are larger. They eat mollusks found on the ocean floor are almost completely dependent upon sea ice to provide them a shelf to launch their feeding forays over the continental shelf.

Other Marine Mammals

Florida Manatee

Family Trichechidea - Manatees

There are several species of these slow swimming and gentle marine mammals. Most live in tropical waters eating sea grass. Through boat strikes and habitat loss most of these species are highly endangered. The front limbs are short flippers and the body tapers to a flat, paddle-shaped tail that distinguishes this species from the related dugong, which posses a fluke-like tail.

dugong

Family Dugongidea - Dugongs

Also known as the "sea cow." These animals are the only marine mammal dependent entirely upon plants for their nutrition. All dugongs grow tusks but these only break the skin, and therefore become visible, in mature males. Like their cousins the manatees they are very slow moving and exist in primarily tropical regions. The large "Stellar Sea Cow" was probably the first Alaskan species to go extinct because of European colonization.

California Sea Otter

Family Mustelindea - Sea otters

The sea otter is the smallest marine mammal in the world. Dense fur that traps air bubbles (for added insulation) is all that allows them to survive in the oceans cold water. They posses a strong, rudder-like tail and large hind-feet that act as flippers. Sea otters have huge appetites and a fast metabolism. They eat a variety of bottom dwelling invertebrates but prefer clams, crabs, and sea urchin. This high metabolic rate help keeps them warm but it also gives them a position as a "keystone species" in kelp forest communities.

Polar Bear

Family Ursus- Polar Bears

The polar bear is the largest living land carnivore in the world today. Here it is grouped with the marine mammals because of its impressive swimming ability and its complete dependence on sea ice for its feeding habitat. The most well known of all bears, the polar bear is distinct for its thick white fur. The fur actually covers skin that is black. The neck of the polar bear is longer than in other species of bears, and the elongated head has small ears. It's long extended neck and broad back side gives the polar bear a "boat like" shape. Polar bears have large strong limbs and huge forepaws which are used as paddles for swimming.

Questions to Research

  1. Select one species from the family phocidea.  Describe the details of their geographic range, feeding strategies, breeding behaviors.

  2. Select one species from the family otaridea.  Describe the details of their geographic range, feeding strategies, breeding behaviors

  3. Compare and contrast the ways seals and sea lions move (both in the water and out of it).  

  1. All sea lions and several species of seals come on land to give birth and nurse their young.  Go to the Tagging of Pacific Pelagics (TOPP) page for elephant seals.  Examine the arrows on the map to see where these species are during different times of the year.  What time of the year do they have their pups on the beaches of Ano Neuvo (Central California)?

  2. Read the story How to Tag an Elephant Seal.  Do your best to summarize the process.

  3. Males elephant seals can grow up to ten times larger than females.  A dominant alpha male may have as many as one hundred females in his harem. Sub-dominant males will frequently challenge dominant males which occasionally results in loud and violent battles.  Read a description of their reproduction strategies,  watch some video of two males battling and explain what the term sexual dimorphism means.

  4. What does a walrus eat and what does it use its huge tusks for? Click on the link, if you want you can watch a video of it.

  5. Listen to the narrated photo journal about polar bears.   When do polar bears mate?  When and for how long to polar bears come on land to den?  What do they eat while on land?

  6. What is the marine mammal protection act?  What is the endangered species act?  Write compare and contrast statements that examine the similarities and differences.

  7. Several of the marine mammals mentioned on this assignment are facing serious decline in Alaska, for reasons that are not always very clear. Select one of the following and explain some of the possible reasons for their decline.

     

    Many thanks to ARKive.  Most of the images and video clips on this page are from their.  What a great site and a great mission.