Chapter 12

1. Marine Mammals Chapter 12

2. Key Concepts • Mammals have a body covering of hair, maintain a constant warm body temperature, and nourish their young with milk produced by the mammary glands of the mother. • Sea otters have thick coats of fur and feed on marine invertebrates near shore.

3. Key Concepts • Pinnipeds have limbs modified to form flippers, and are better adapted to life at sea than to life on land. • Sirenians are totally aquatic mammals that feed on a variety of aquatic vegetation. • Cetaceans have a fish-like body shape and are the mammals most suited to life in the sea.

4. Key Concepts • Special physiological adaptations allow cetaceans to dive to great depths and to remain submerged for long periods. • Cetaceans are intelligent animals that display a range of behaviors for communication and investigating their environment. • Some cetaceans use echolocation to navigate, find prey, and avoid predators.

5. Key Concepts • Baleen whales have plates of baleen instead of teeth and feed primarily on plankton, such as krill. • Toothed whales include the large sperm whales and the familiar dolphins and porpoises. • Dolphins are intelligent animals that are capable of learning and sophisticated intraspecies communication.

6. Characteristics of Marine Mammals • Class Mammalia • Most have an insulating body covering of hair • Homeothermic • allows activity day and night, and adaptation to a wide range of habitats • Mothers feed their young with milk • mammary glands—special glands in the female that secrete milk

7. Characteristics of Marine Mammals • Most marine mammals are placental mammals—animals that retain their young inside their body until they are ready to be born • placenta—an organ present only during pregnancy that sustains the young • Feed at various trophic levels

8. Sea Otters • Have thick fur with an underlying air layer for insulation (instead of blubber) • Short, erect ears • Dexterous 5-fingered forelimbs • Well-defined hind limbs with fin-like feet • Usually stay within a mile of shore, near coastal reefs and kelp beds

9. Sea Otters • Females normally give birth to 1 pup on shoreline rocks, and it soon follows its mother into the sea • Consume nearly 25% of their body weight in food each day • eat sea urchins, molluscs, crustaceans, some species of fish • Diurnal, gregarious, vocal and playful • Nearly hunted to extinction for fur

10. Pinnipeds: Seals, Sea Lions, and Walruses • Suborder Pinnipedia (e.g. seals, elephant seals, sea lions, walruses) • pinniped—”feather-footed” • Have 4 limbs like terrestrial animals, but are more at home in the water • Come shore to give birth and molt • most also mate on shore, and some sleep on land or ice floes to avoid entirely aquatic predators

11. Pinnipeds: Seals, Sea Lions, and Walruses • Eat fish, invertebrates; some eat other homeothermic animals • Eaten by sharks, killer whales and humans

12. Pinniped Characteristics • 3 families: • eared seals (Otariidae) • true seals (Phocidae) • walruses (Odobenidae) • Eared seals have small external ears and swim using their forelimbs • Phocids (true seals) lack external ears and swim with a sculling movement of their hind flippers

13. Pinniped Characteristics • Walruses swim with a combination of the 2 methods • Pinnipeds have spindle-shaped bodies • Many have several thick layers of subcutaneous fat • Round is carried on a distinct neck • Large brains, well-developed senses • 2 pairs of limbs are modified into flippers

14. Swimming and Diving • Fast swimmers and expert divers • Adaptations for diving • exhale before diving to decrease buoyancy • metabolism slows by 20% and heart rate decreases while under water • blood redistributed to direct oxygen to vital organs such as the brain and heart • Weddell seals and northern elephant seals known for deep diving

15. Reproduction in Pinnipeds • Most congregate on well-established breeding beaches to mate/give birth • Some species are polygynous—bulls establish harems of 15 or more females • Males arrive to establish territories; females arrive, give birth to pups, then mate again

16. Reproduction in Pinnipeds • Gestation = 9-12 months • Lactation period (length of time pups nurse) depends on species and habitat • coldest habitats = shortest lactation • nursing stresses the mother and she loses weight • some breed on pack ice, and must wean pups before it breaks up and becomes dangerous to the pups

17. Eared Seals • Sea lions • e.g. California sea lion, the intelligent trained seal seen in zoos and circuses • highly social; congregate when on shore • Fur seals • distinguished from sea lions by thick, wooly undercoats • coats are prized in the fur market, so hunting is limited to avoid decimating the population of fur seals

18. Phocids, or True Seals • Forelimbs are set closer to the head and smaller than the hind limbs • less adapted to life on land • move on land by dragging their bodies • Most congregate during breeding season; males establish territories but mate with only 1 female • Most abundant: crabeater seal, which actually eats plankton such as krill

20. Phocids, or True Seals • Harbor seals are a familiar type • Harp seal pups have a white coat, and are thus prized in the fur market

22. Phocids, or True Seals • Leopard seal is the only phocid that eats homeothermic prey, including other phocids, penguins, and seabirds

24. Phocids, or True Seals • Elephant seals are the largest, and bulls have a unique proboscis that amplifies their roar and attracts mates

26. Walruses • Lack external ears but have a distinct neck and hind limbs that can be used for walking on land • Canine teeth of the upper jaws of males have developed into tusks • used to fight with other males or hoist the animal onto ice floes • Typical family group = 1 dominant bull with a harem of up to 3 females and 6 calves of various ages

28. Walruses • Reproduction • 11-month gestation period • 1 or 2 calves stay with the mother until they are 4 or 5 years old • old bulls sometimes kill young • Found in the Arctic region • Eat fishes, crustaceans, molluscs and echinoderms • Eskimos are allowed to hunt them for meat, but not for their tusks

29. Sirens: Manatees and Dugongs • Order Sirenia (sirenians) • Confined to coastal areas and estuaries of tropical seas • Similarities to whales • streamlined, practically hairless bodies • forelimbs that form flippers, tail flukes • vestigial pelvis without hind limbs • Completely aquatic • Gentle and often trusting of humans

30. Dugongs • Strictly marine • Live in coastal areas of Indian Ocean • Feed on shallow-water grasses • Dugongs are distinguished anatomically from manatees by: • larger heads • shorter flippers • notched tail

31. Manatees • Inhabit both the sea and inland rivers and lakes • Have smaller heads, longer flippers than dugong, and rounded tails • Mate and give birth under water • male remains with female after breeding • Strict vegetarians that consume large amounts of shallow-water plants • Motorboat propellers are the greatest danger to northern manatees

33. Steller’s Sea Cow • This Arctic sirenian is now extinct • Species was first observed and recorded by Georg Wilhelm Steller • After his expedition brought furs from the Commander Islands, this area developed a reputation for furs which attracted hunters • The hunters used Steller’s Sea Cow as a food source, and hunted the species to extinction

34. Cetaceans: Whales and their Relatives • Mammals most adapted to life at sea • E.g. whales, dolphins, porpoises • Cetaceans have fascinated humans for centuries • Cetaceans have frequently appeared in art and literature

36. General Characteristics of Cetaceans • Thought to have evolved from terrestrial carnivores (now extinct) • Bodies closely resemble those of fishes and are very streamlined • blowhole—nostril at the top of the head • uniformly thick layer of subcutaneous blubber • streamlining of body results in lack of neck, inability to move head separately • internal ears with wax plugs

37. General Characteristics of Cetaceans • Bodies closely resemble those of fishes and are very streamlined (continued) • essentially hairless, except for a few hairs on the head • lack of sweat glands conserves water • forelimbs modified into stabilizing flippers • tail composed of flat flukes composed of dense connective tissue is the main organ of propulsion • countercurrent circulatory system with cold blood directed to un-insulated flippers conserves heat

39. Adaptations for Diving • Prior to dive, a whale inhales an enormous breath, oxygen is rapidly transferred to blood, and the whale exhales to reduce buoyancy • Proportionately large lungs with many alveoli—small air sacs • increases internal lung surface area exposed to blood vessels • allows for more efficient diffusion of gases into and out of blood

40. Adaptations for Diving • Lungs and rib cage structured to collapse easily upon descent • contain little air during a dive • animal avoids problems of compression and decompression while diving/surfacing • During a dive: • metabolism and heart rate decrease • blood is preferentially shunted to vital organs and tissues (e.g. brain, spinal cord)

41. Adaptations for Diving • Medulla oblongata is less sensitive to CO2 levels in blood • can hold breath without urge to breathe • Large amounts of hemoglobin and myoglobin • hemoglobin—molecule in red blood cells responsible for carrying oxygen • myoglobin—molecule in muscle tissue that is a reservoir of oxygen for muscle activity

42. Adaptations for Diving • Muscles less sensitive to lactic acid • lactic acid—a waste produced during vigorous or extended muscle activity in the presence of insufficient oxygen • Exhalation of mucus from blowhole upon surfacing helps eliminate nitrogen from inhaled air, preventing the bends • the bends—condition in which nitrogen gas dissolved in blood comes out of solution and forms gas bubbles

43. Adaptations for Diving • Water is prevented from entering respiratory passages • larynx opens into the nasal chambers instead of the back of the throat • cetaceans can open their mouths under water without food or water entering respiratory passages

45. Cetacean Behaviors • Spy hopping—sticking the head straight up out of the water and surveying the surroundings • position maintained with buoyancy control and positioning of pectoral fins, tail flukes • occurs when cetacean is interested in a passing boat or other object • may help animal to get bearings in coastal waters

47. Cetacean Behaviors • Breaching—completely or almost completely leaving the water • animal accelerates under water and then hits the surface, exiting the water • may be used to establish dominance or communicate arrival/leaving • serial breaching—breaching several times in a row • head lunge—breaking the surface and falling forward instead of backward

49. Cetacean Behaviors • Slapping - aggressive • tail slapping or lobbing—lifting the tail and slapping it forcefully on the surface of the water • tail cocking—cocking the tail in the air and bringing it down upon an opponent • peduncle slap—swinging the rear portion of the body out of the water, and then dropping it down sideways on the water or another whale