© 2006 Thomson-Brooks Cole Chapter 12 Marine Mammals

© 2006 Thomson-Brooks Cole

Chapter 12

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.


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




• Harbor seals are a familiar type• Harp seal pups have a white coat, and

are thus prized in the fur market




• Leopard seal is the only phocid that eats homeothermic prey, including other phocids, penguins, and seabirds




• 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



• 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)



• 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



• 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



• 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



Cetacean Behaviors

• Slapping - aggressive (continued)– peduncle—the part of the whale’s body

closest to the tail fluke– 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 – non-aggressive– 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


Reproduction and Development

• Many travel in pods (groups) of adults and young

• 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


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 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, then straining 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



Baleen Whales

• Right whales (family Balaenidae)– lack dorsal fins and grooves on throat and

chest– name derived from identification of these

whales as the “right whales” for hunting– one species, the Greenland or bowhead

whale, is the rarest of all whales


Baleen Whales

• Rorquals (family Balenopteridae)– have dorsal fin and ventral grooves

• ventral grooves allow the throat to expand while the animal is feeding

– slender, streamlined, fast swimmers– blue whale is the largest whale– fin whale is second largest– humpback whale has hump on its back,

bosses (bumps) on its snout, and very long pectoral fins



Baleen Whales

• Gray whale (Eschrictius gibbosus)– only eastern Pacific population survived

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

• Sperm whales (Physeter macrocephalus)– 3rd 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– 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, are found in northern polar seas– male narwhals have a tusk developed

from 1 of 2 tooth buds; narwhals also inhabit Arctic waters



Toothed Whales

• Porpoises (family Phocaenidae)– 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

• 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



Echolocation

• Echoes provide 4 types of information:– direction from which echo is coming– change in frequency– amplitude– time elapsed before the sound returns

• This reveals object’s range, bearing, size, shape, texture and density

• Traveling dolphins move their heads side to side and up and down, scanning for objects

Documents

© 2006 Thomson-Brooks Cole Chapter 12 Marine Mammals