Marine Mammals

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.

 Polar bears feed mainly on seals and are top predators in arctic food chains.

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

feed primarily on plankton, such as krill.

 Toothed whales have teeth allowing them to feed on larger prey, primarily fish and squid, although killer whales will eat marine birds and mammals.  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 (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

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

 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

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

 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

 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

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

Pinnipeds: Seals, Sea Lions, and Walruses

 Eat fish, larger invertebrates; some eat other homeothermic animals  Natural predators include 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 head is carried on a distinct neck  Large brains, well-developed senses  2 pairs of limbs are modified into flippers

Swimming and Diving

 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

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 conceived the previous year, then mate again

Reproduction in Pinnipeds

 Seasonal delayed implantation – allows mother to adjust gestation period into annual time frame  Lactation period (length of time pups nurse) depends on species and habitat   coldest habitats = shortest lactation nursing physiologically 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  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

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

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 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

Walruses

 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

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

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.

 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

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

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

 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

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

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

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

Adaptations for Diving

(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)

Adaptations for Diving

 Medulla oblongata (portion of brain that controls breathing) is less sensitive to CO 2 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

 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  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

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

 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

 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

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

Reproduction and Development

      Knowledge comes mostly from observations of small whales in captivity Baleen whales  Mate and give birth in same locality and same time of year, gestation period 10-13 months Toothed whales  Breeding occurs throughout the year, gestation period 7-10 months Usually bear 1 offspring at a time Nursed on extremely rich milk    40-50% fat, 10-12% protein infant grows rapidly can produce sufficient body heat until blubber layer has developed Many travel in pods (groups) of adults and young

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

Baleen Whales

 Enormous mouths with plates of baleen  each plate has an elongated triangular shape and is anchored at its base to the gum of the upper jaw  composed of keratin—a tough protein—in fibers fused except at the inner edge, where they form a fringe   hundreds of plates form a tight mesh used to capture plankton, especially krill, and fish

Baleen Whales

 Whale feeds by swimming open-mouthed through the water into dense groups of krill and fish, then strains out water through baleen  bubble net: a ring of bubbles blown by a humpback whale to trap krill near the surface for collection  Baleen is protected by the underlip when the whale is not feeding

Krill Bubbles Whale ascends in a spiral pattern blowing bubbles from its blowhole Stepped Art Fig. 12-15, p. 344

Baleen Whales

 Right Whales and Bowhead Whales (family Balaenidae)  distinguished by lack of dorsal fins and grooves on throat and chest  name derived from identification of these whales as the “right whales” for hunting  the bowhead whale is the rarest of all whales

Baleen Whales

 have dorsal fin and ventral grooves lacking in balaenids      ventral grooves allow the throat to expand while the animal is feeding slender, streamlined, fast swimmers blue whale is the largest whale, maybe the largest animal that has ever lived, 24-30 meters (80 – 100 ft) long, weighing more than 100 tons fin whale is second largest humpback whale has hump on its back, bosses (bumps) on its snout, and very long pectoral fins, inhabits coastal waters frequently enters harbors and ventures up river mouths

 modern whaling techniques allowed for effective hunting of large rorquals  blue whale given worldwide protection in 1966 by the International Whaling Commission

Baleen Whales

 Gray whale (Eschrictius gibbosus)  only eastern Pacific population survives today after western Pacific and Atlantic populations were hunted to extinction  migrate from summer feeding grounds in Bering Sea to waters off Baja California to mate and give birth  referred to as mossback whales owing to large accumulations of barnacles on their skin

Toothed Whales

  Include sperm whales, dolphins, porpoises, killer whales and narwhals Sperm whales ( Physeter macrocephalus; family Physeteridae )  3 rd largest animal with massive blunt snout     have a series of humps on the rear third of the body, no real dorsal fin aggressive attackers of squid and fish, occasionally whalers in small boats polygynous – males accompanied by several females named for spermaceti—an oily, wax-like substance in the animal’s head

Toothed Whales

 Sperm whales (continued)  ambergris: a digestive product; a secretion thought to function in protecting the enormous digestive system from undigested squid beaks and cuttlefish cuttlebone  spermaceti was sought as a high-grade wax; ambergris, as a base for perfumes

Toothed Whales

 White whales (family Monodontidae)  Beluga whales   are unique for their white color and ability to bend neck, are found in northern polar seas main predators are killer whales and polar bears  Narwhals    close relatives of beluga whales male have tusk developed from 1 of 2 tooth buds narwhals also inhabit Arctic waters, eskimos only remaining predators

Toothed Whales

 Porpoises (family Phocaenidae)  Related to dolphins, both in same superfamily, Delphinoidea  porpoises have a rounded head with no beak (dolphins have a beak)   harbor porpoises are small cetaceans known for great intelligence, and have a wide distribution in the North Atlantic Dall’s porpoise is perhaps the first animal to be protected by law – Europeans once considered it a rare delicacy

Toothed Whales

 Dolphins (family Delphinidae)  collectively referred to as delphinids  common dolphin has a definite beak separated from the snout by a groove; known for encircling and following ships   bottlenose dolphins are used in research on cetacean intelligence, and as performing animals at aquariums orca (killer whale) is the largest dolphin; only cetacean that eats homeothermic prey (e.g. seals, sea lions, penguins)

Toothed Whales

 Dolphins (continued)  pilot whales have a globular head, projecting forehead, and muzzle that forms a small beak  known for beaching themselves in large numbers

Echolocation

 Ears are modified to receive a wide range of underwater vibrations  Echolocation allows cetaceans to distinguish and hone in on objects from distances of several hundred meters  Dolphins emit clicking sounds  orientation clicks: low-frequency clicks that give the animal a general idea of its surroundings  discrimination clicks: high-frequency clicks that give the animal a precise picture of a particular object

Echolocation

 No vocal cords; sounds are produced by a ring of muscles in the larynx, which allows control of air flow  Sounds are directed by being focused in the melon  melon: an oval mass of fatty, waxy material located between the blowhole and the end of the head  Clicking sounds bounce off objects; echoes picked up by sensitive areas on the lower jaw

 direction from which echo is coming  change in frequency  amplitude  time elapsed before the sound returns  With this information, dolphin determines object’s range, bearing, size, shape, texture and density  Traveling dolphins move their heads side to side and up and down, scanning for objects