© 2006 Thomson-Brooks Cole Chapter 12 Marine Mammals

© 2006 Thomson-Brooks Cole Characteristics of Marine Mammals Class Mammalia Characteristics –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)

© 2006 Thomson-Brooks Cole 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

© 2006 Thomson-Brooks Cole Sea Otters Order Carnivora Have thick fur with an underlying air layer for insulation (instead of blubber) Short, erect ears Usually stay within a mile of shore, near coastal reefs and kelp beds Females normally give birth to 1 pup on shoreline rocks, and it soon follows its mother into the sea Nearly hunted to extinction for fur

© 2006 Thomson-Brooks Cole 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

© 2006 Thomson-Brooks Cole Pinnipeds: Seals, Sea Lions, and Walruses Eat fish, invertebrates; some eat other homeothermic animals Eaten by sharks, killer whales and humans

© 2006 Thomson-Brooks Cole 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; flippers do not allow for fast movement on land

© 2006 Thomson-Brooks Cole 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

© 2006 Thomson-Brooks Cole 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

© 2006 Thomson-Brooks Cole Reproduction in Pinnipeds Interesting Facts: (Not for testing) 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

© 2006 Thomson-Brooks Cole 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

© 2006 Thomson-Brooks Cole 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

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

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

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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

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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

© 2006 Thomson-Brooks Cole 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

© 2006 Thomson-Brooks Cole 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

© 2006 Thomson-Brooks Cole 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

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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