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Marine Mammals. Chapter 12. 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.
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Marine Mammals Chapter 12
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.
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.
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.
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.
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
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
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
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
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
Pinnipeds: Seals, Sea Lions, and Walruses • Eat fish, invertebrates; some eat other homeothermic animals • Eaten by sharks, killer whales and humans
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
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
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
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
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
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
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
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
Phocids, or True Seals • Leopard seal is the only phocid that eats homeothermic prey, including other phocids, penguins, and seabirds
Phocids, or True Seals • Elephant seals are the largest, and bulls have a unique proboscis that amplifies their roar and attracts mates
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
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
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
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
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
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
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
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
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
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
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)
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
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
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
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
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
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