Marine Mammals Lesson 9.5

• Diverse groups of landmammals that have adaptedto life in the ocean: all havehair, bear live young andnurse their offspring

• They include:

-sea otters and polar bears

-seals, sea lions and walruses

-manatees and dugongs

-whales, dolphins and porpoises

Sea Otters• Sea otter is the smallest marine mammal and hasno blubber layer• insulation from air trappedin its thick fur.• Otters use tools like rocksto crush shells of abaloneand other shellfish• Otters help to keep kelpforests healthy by eating sea urchins, which graze on kelp• This helps preservebiodiversity of ocean food web• Hunted for its fur and killedby fishermen, its numbers have declined

Polar Bears • Polar bears are semi-aquatic• spend much of their liveson drifting Arctic ice. • They feed primarily on seals, butalso whale and walrus carcasses. • Male polar bears may grow to10 feet tall and weigh over 1400 lb. Females may reach seven feet andweigh 650 lb.• Polar bears have been known toswim 100 miles at a stretch. • They are found in the Arctic, Alaska,Canada, Russia, Greenland, andNorway. • Humans are their main predators• Global warming threatens polar bear populations by melting the seaice, which is their main habitat.

Seals, Sea Lions and Walruses• Have paddle-shaped flippers for swimming, but must rest and breed on land• ”Blubber” = thick layer of fat forinsulation, food reserve and buoyancy• Many are large, which helps toconserve body heat in coldwaters• Elephant seals are the largest:males can be 20 ft long and up to 5,000 lb. • Elephant seals can dive for 1.5hours without coming up for air• Walrus tusks are used for defenseand to anchor the animal to the ice.

M. Parker

Elephant seal research at Sonoma State University

Dr. Dan Crocker with a bull elephant seal (anesthetized!) at Ańo Nuevo State Park in San Mateo County, fitting it with tracking devices to study its diving physiology and migration patterns. The scars on the seal’s back and snout are from fighting with other males during the breeding season, which is the only time that males are found on land. Females stay longer to give birth and wean their pups.

Manatees and Dugongs• Sirenians, also known as “sea cows,” are named for mermaids• These gentle mammals are related toelephants!• only marine mammals that are strictvegetarians, feeding on sea grasses andother vegetation• Manatees larger, up to 15 ft long andover 1,300 lb.• Hunted by humans for oil-rich blubber and meat• Slow reproduction– 1 calf every 3 yr.• Manatees found in Atlantic Ocean, theAmazon, Florida, S. Africa• Dugongs only marine, from E. Africato western Pacific islands.• Manatees have been injured and killedby collisions with boat propellers in Florida; now have speed restrictions insome manatee habitats

Dolphins, Porpoises and Whales• Along with sirenians, mostcomplete transition to marine life;spend their entire lives in the water.• convergent evolution: theseanimals look very fish-like, butbreathe air, are warm-blooded andnurse their young.• Front flippers only, some havedorsal fins like fish• Blubber for insulation, buoyancy• Hair almost absent• Nostrils on top of head = blow-

hole• Many highly intelligent– malehumpback “songs” thought tocommunicate mating fitness• Can be heard for 100 miles!

Some of the world’s whales

Baleen whales

• Largest whales on earth arebaleen, which eat tiny shrimp-likeanimals called krill • No teeth, but rows of flexible fibrous plates made of keratin thathang from the upper jaws. • It filter-feeds by gulping a hugemouthful of water and squeezing it out through the baleen to strain outfood particles• Largest baleen whales are theblue whales -- can reach lengths of80-110 ft; weight up to 140 tons!(That is 280,000 lb!)• If the average teenager weighed140 lb, 2000 teens = one blue whale!

krill

• 80 species of toothed whales, including dolphins and porpoises

• Numbers of teeth vary from 2 (narwhal) to over 100 in some species of dolphins

• Most smaller than baleen whales, although killer whales can reach 26

• Largest is sperm whale (“Moby Dick”) at 60+ ft. • Toothed whales eat fish, squid, shrimp, penguins, pinnipeds.

March 2012 whale hunting in the Southern Ocean near Australia

Humans have hunted whales for centuriesSubsistence vs. commercial hunting (Inuits vs. Japan, Norway, Iceland)Very controversial animal rights issue (Green Peace, Sea Shepherd)

A happy note: the annual gray whale spring migration of females and calves, from Baja California to Alaska is happening now.

You can watch this migration on the Sonoma and Marin coasts!

gray whale and calf