Marine Mammals: Characteristics, Diversity, and Conservation

1. Who, What, When, Where, Why, and How of Marine Mammals • Who studies mammals? • What are the characteristics of mammals? • Where are most marine mammals found? Think diversity. • When do whales migrate? • Why do whales migrate? • How are dolphins and whales related?

2. Chapter 12 Marine Mammals

3. Characteristics of Marine Mammals • Class Mammalia • Most have an insulating body covering of hair • Homeothermic (warm body temperature) • 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

4. Characteristics of Marine Mammals • 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

5. Sea Otters • Sea Otters (Enhydra lutris; order Carnivora) • Found along California coast as far north as the Aleutian Islands • Short, erect ears • Dexterous 5-fingered forelimbs • Well-defined hind limbs with fin-like feet • Have thick fur with an underlying air layer for insulation (instead of blubber) • Usually stay within a mile of shore, near coastal reefs and kelp beds

6. 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

7. Polar Bears • Polar Bears (Ursus maritimus; order Carnivora) • Top predators in Arctic food chains • Large, adult male may grow to ~3 meters (9.9 ft) and weigh 725 kilograms (1,595 lbs) • Live on shifting ice sheets and floes • Well adapted to cold environment • large body (small surface area to volume) • black skin absorbs radiant energy • dense layer of underfur

8. Polar Bears • Diet consists primarily of seals • Mate in spring, males compete aggressively with other males for available females • Females give birth usually to 2 cubs each weighing 1 lbs • Global warming causing shrinkage of ice sheets on which polar bears hunt • Although population is now estimated at 40,000 (was 10,000 in the 1960’s) polar bears are considered endangered

9. Pinnipeds: Seals, Sea Lions, and Walruses • Order carnivora; Suborder Pinnipedia • include seals, elephant seals, sea lions and 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

10. Pinnipeds: Seals, Sea Lions, and Walruses • Eat fish, larger invertebrates; some eat other homeothermic animals • Natural predators include sharks, killer whales and humans

11. 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

12. 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 head is carried on a distinct neck • Large brains, well-developed senses • 2 pairs of limbs are modified into flippers

13. 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 to conserve oxygen • during dive, blood is redistributed to direct oxygen to vital organs such as the brain and heart • Have 10 to 30 times more oxygen in their muscles than humans

14. Eared Seals • Sea lions • coarse coat of nothing but hair • 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

15. Phocids, or True Seals • Forelimbs are set closer to the head and smaller than the hind limbs • less adapted to life on land, can’t move around very well • 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

17. 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 • Leopard seal is only phocid that eats homeothermic prey, penguins, sea birds and other seals make up bulk of diet

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

22. Walruses • Lack external ears but have a distinct neck and hind limbs that can be used for walking on land • Can grow to 3 to 5 meters (10 to 16 ft) in length and weigh up to 1,364 kilograms (3,000 lbs) • 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

24. 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 • Native people are allowed to hunt them for meat, but not for their tusks

25. Sirens: Manatees and Dugongs • Order Sirenia (sirenians) • Now 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, helpless on land

26. Sirens: Manatees and Dugongs • Gentle and often trusting of humans • Two families: one represented by the manatees (family Trichechidae) in Atlantic Ocean and Caribbean Sea; the other by the dugongs (family Dugongidae) of the Indian Ocean.

27. 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 • Only one species

28. Manatees • Three species • Inhabit both the sea and inland rivers and lakes • Mate and give birth under water • male remains with female after breeding • female gives birth to single calf after 11 months gestation period • Strict vegetarians that consume large amounts of shallow-water plants • Motorboat propellers are the greatest danger to northern manatees

30. 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

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

33. 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

34. 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 and regulates vertical movement • countercurrent circulatory system with cold blood directed to un-insulated flippers conserves heat

35. Flipper Artery Vein Artery Tail fluke Vein Artery Blood flow Warm arterial blood from the animal's body core transfers heat to the cooler venous blood Heat flow Heat flow Blood flow Vein Stepped Art Fig. 12-10, p. 338

36. Adaptations for Diving • Lungs are smaller in proportion to their body size (compared to humans) and can exchange 80 to 90% of oxygen with their blood • 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)

37. Adaptations for Diving • Medulla oblongata (portion of brain that controls breathing) 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

38. 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

39. 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

41. Cetacean Behaviors • Spy hopping: sticking the head straight up out of the water and surveying the surroundings • uses strong fluke to push itself partially out of water, 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 whale to establish bearings in coastal waters

43. Cetacean Behaviors • Breaching: completely or almost completely leaving the water • whale 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

45. Cetacean Behaviors • Slapping • tail slapping or lobbing: lifting the tail and slapping it forcefully on the surface of the water, creating huge splash and loud noise, associated with marking position, interpreted as an aggressive behavior • tail cocking: cocking the tail in the air and bringing it down upon an opponent, also considered aggressive behavior • 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

47. Cetacean Behaviors • Slapping (continued) • 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 • tail slashing and tail swishing: moving the tail from side to side across the surface of the water to create turbulence • whale may arch its body and then bring the flukes above the surface • straight up so ventral surface is visible = fluke up • fluke clears the water but remains turned down = fluke down

48. Cetacean Behaviors • Slapping (continued) • flipper flapping: rolling over onto the back and flapping the flippers in the air • pectoral stroking: stroking the body of another whale with the pectoral fins • occurs between mother and calf or during courtship and mating • both flipper flapping and pectoral stroking are thought to be forms of communication

49. Types of Whales • 2 suborders • Mysticeti – baleen whales • Odontoceti – toothed whales • Baleen whales lack teeth, and filter food from the water using baleen • largest whales are of this type • Toothed whales feed on larger prey • e.g., dolphins, killer whales