Marine Mammals

Key ConceptsMammals 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 ConceptsPinnipeds 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 ConceptsSpecial 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 ConceptsBaleen whales have plates of baleen instead of teeth and 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 MammalsClass MammaliaMost have an insulating body covering of hairHomeothermic (warm body temperature)

allows activity day and night, and adaptation to a wide range of habitats

Mothers feed their young with milkmammary glands: special glands in the female

that secrete milk

Characteristics of Marine MammalsMarine mammals are placental mammals—

animals that retain their young inside their body until they are ready to be bornplacenta: an organ present only during

pregnancy that sustains the youngFeed at various trophic levels

Sea OttersSea Otters (Enhydra lutris; order Carnivora)Found along California coast as far north as

the Aleutian IslandsShort, erect earsDexterous 5-fingered forelimbsWell-defined hind limbs with fin-like feetHave 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 OttersFemales 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 dayeat sea urchins, molluscs, crustaceans, some

species of fishDiurnal, gregarious, vocal and playfulNearly hunted to extinction for fur

Polar BearsPolar Bears (Ursus maritimus; order Carnivora)

Top predators in Arctic food chainsLarge, adult male may grow to ~3 meters

(9.9 ft) and weigh 725 kilograms (1,595 lbs)Live on shifting ice sheets and floesWell adapted to cold environment

large body (small surface area to volume)black skin absorbs radiant energydense layer of underfur

Polar BearsDiet consists primarily of sealsMate in spring, males compete aggressively

with other males for available femalesFemales give birth usually to 2 cubs each

weighing 1 lbsGlobal warming causing shrinkage of ice

sheets on which polar bears huntAlthough population is now estimated at

40,000 (was 10,000 in the 1960’s) polar bears are considered endangered

Pinnipeds: Seals, Sea Lions, and WalrusesOrder 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 waterCome 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 WalrusesEat fish, larger invertebrates; some eat other

homeothermic animalsNatural predators include sharks, killer

whales and humans

Pinniped Characteristics3 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 CharacteristicsWalruses swim with a combination of the 2

methodsPinnipeds have spindle-shaped bodiesMany have several thick layers of

subcutaneous fatRound head is carried on a distinct neckLarge brains, well-developed senses2 pairs of limbs are modified into flippers

Swimming and DivingFast swimmers and expert diversAdaptations for diving

exhale before diving to decrease buoyancymetabolism slows by 20% and heart rate

decreases while under water to conserve oxygenduring dive, blood is redistributed to direct

oxygen to vital organs such as the brain and heartHave 10 to 30 times more oxygen in their

muscles than humans

Reproduction in PinnipedsMost congregate on well-established

breeding beaches to mate/give birthSome species are polygynous—bulls establish

harems of 15 or more femalesMales arrive to establish territories; females

arrive, give birth to pups conceived the previous year, then mate again

Reproduction in PinnipedsGestation = approximately 1 yearSeasonal delayed implantation – allows mother

to adjust gestation period into annual time frame

Lactation period (length of time pups nurse) depends on species and habitatcoldest habitats = shortest lactationnursing physiologically stresses the mother and

she loses weightsome breed on pack ice, and must wean pups

before it breaks up and becomes dangerous to the pups

Eared SealsSea lions

coarse coat of nothing but haire.g., California sea lion, the intelligent trained

seal seen in zoos and circuseshighly social; congregate when on shore

Fur sealsdistinguished from sea lions by thick, wooly

undercoatscoats are prized in the fur market, so hunting is

limited to avoid decimating the population of fur seals

Phocids, or True SealsForelimbs are set closer to the head and

smaller than the hind limbsless adapted to life on landmove 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 SealsHarbor seals are a familiar typeHarp seal pups have a white coat, and are

thus prized in the fur marketLeopard seal is only phocid that eats

homeothermic prey, penguins, sea birds and other seals make up bulk of diet

Phocids, or True SealsElephant seals are the largest, and bulls have

a unique proboscis that amplifies their roar and attracts mates

WalrusesLack 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 tusksused to fight with other males or hoist the animal

onto ice floesTypical family group = 1 dominant bull with

a harem of up to 3 females and 6 calves of various ages

WalrusesReproduction11-month gestation period1 or 2 calves stay with the mother until they are 4

or 5 years oldold bulls sometimes kill young

Found in the Arctic regionEat fishes, crustaceans, molluscs and

echinodermsNative people are allowed to hunt them for

meat, but not for their tusks

Sirens: Manatees and DugongsOrder Sirenia (sirenians)Now confined to coastal areas and estuaries

of tropical seasSimilarities to whales

streamlined, practically hairless bodiesforelimbs that form flippers, tail flukesvestigial pelvis without hind limbs

Completely aquatic, helpless on land

Sirens: Manatees and DugongsGentle and often trusting of humansTwo 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.

DugongsStrictly marineLive in coastal areas of Indian OceanFeed on shallow-water grassesDugongs are distinguished anatomically from

manatees by:larger headsshorter flippersnotched tail

Only one species

ManateesThree speciesInhabit both the sea and inland rivers and

lakesMate and give birth under water

male remains with female after breedingfemale gives birth to single calf after 11 months

gestation periodStrict vegetarians that consume large

amounts of shallow-water plantsMotorboat propellers are the greatest

danger to northern manatees

Steller’s Sea CowThis Arctic sirenian is now extinctSpecies was first observed and recorded by

Georg Wilhelm StellerAfter 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, porpoisesMammals most adapted to life at seaCetaceans have fascinated humans for

centuriesCetaceans have frequently appeared in art

and literature

General Characteristics of CetaceansThought to have evolved from terrestrial

carnivores (now extinct)Bodies closely resemble those of fishes and

are very streamlinedblowhole: nostril at the top of the headuniformly thick layer of subcutaneous blubberstreamlining of body results in lack of neck,

inability to move head separatelyinternal ears with wax plugs

General Characteristics of CetaceansBodies closely resemble those of fishes and are very streamlined (continued)essentially hairless, except for a few hairs on the

headlack of sweat glands conserves waterforelimbs modified into stabilizing flipperstail 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

Tail fluke

ArteryVein

ArteryVein

Warm arterial blood from the animal's body coretransfers heat to the cooler venous blood

Bloodflow

Heat flow Heat flow

Bloodflow

Vein

Artery

Stepped Art

Fig. 12-10, p. 338

Adaptations for DivingLungs 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 descentcontain little air during a diveanimal avoids problems of compression and

decompression while diving/surfacingDuring a dive:

metabolism and heart rate decreaseblood is preferentially shunted to vital organs and

tissues (e.g., brain, spinal cord)

Adaptations for DivingMedulla oblongata (portion of brain that

controls breathing) is less sensitive to CO2 levels in bloodcan hold breath without urge to breathe

Large amounts of hemoglobin and myoglobinhemoglobin: molecule in red blood cells

responsible for carrying oxygenmyoglobin: molecule in muscle tissue that is a

reservoir of oxygen for muscle activity

Adaptations for DivingMuscles less sensitive to lactic acidlactic 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 bendsthe bends: condition in which nitrogen gas

dissolved in blood comes out of solution and forms gas bubbles

Adaptations for DivingWater is prevented from entering respiratory

passageslarynx opens into the nasal chambers instead

of the back of the throatcetaceans can open their mouths under water

without food or water entering respiratory passages

Cetacean BehaviorsSpy hopping: sticking the head straight up

out of the water and surveying the surroundingsuses 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 BehaviorsBreaching: completely or almost completely

leaving the waterwhale accelerates under water and then hits

the surface, exiting the watermay be used to establish dominance or

communicate arrival/leavingserial breaching: breaching several times in a

rowhead lunge: breaking the surface and falling

forward instead of backward

Cetacean BehaviorsSlapping 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

Cetacean BehaviorsSlapping (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

Cetacean BehaviorsSlapping (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 matingboth 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 whalesMate and give birth in same locality and same time of year,

gestation period 10-13 monthsToothed whales

Breeding occurs throughout the year, gestation period 7-10 months

Usually bear 1 offspring at a timeNursed on extremely rich milk

40-50% fat, 10-12% protein infant grows rapidlycan produce sufficient body heat until blubber layer has

developedMany travel in pods (groups) of adults and young

Types of Whales2 suborders

Mysticeti – baleen whalesOdontoceti – toothed whales

Baleen whales lack teeth, and filter food from the water using baleenlargest whales are of this type

Toothed whales feed on larger preye.g., dolphins, killer whales

Baleen WhalesEnormous 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 meshused to capture plankton, especially krill, and

fish

Baleen WhalesWhale feeds by swimming open-mouthed

through the water into dense groups of krill and fish, then strains out water through baleenbubble 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

Whale ascends in a spiral pattern blowing bubbles from its blowhole

Bubbles

Krill

Stepped Art

Fig. 12-15, p. 344

Baleen WhalesRight Whales and Bowhead Whales (family

Balaenidae)distinguished by lack of dorsal fins and grooves

on throat and chestname derived from identification of these

whales as the “right whales” for huntingthe bowhead whale is the rarest of all whales

Baleen WhalesRorquals (family Balenopteridae)have dorsal fin and ventral grooves lacking in

balaenids ventral grooves allow the throat to expand while the

animal is feedingslender, streamlined, fast swimmersblue 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 largesthumpback 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

Baleen WhalesRorquals (family Balenopteridae) (continued)modern whaling techniques allowed for effective

hunting of large rorqualsblue whale given worldwide protection in 1966 by

the International Whaling Commission

Baleen WhalesGray 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 WhalesInclude sperm whales, dolphins,

porpoises, killer whales and narwhals Sperm whales (Physeter macrocephalus;

family Physeteridae)3rd largest animal with massive blunt snouthave a series of humps on the rear third of the

body, no real dorsal finaggressive attackers of squid and fish,

occasionally whalers in small boatspolygynous – males accompanied by several

femalesnamed for spermaceti—an oily, wax-like

substance in the animal’s head

Toothed WhalesSperm 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 WhalesWhite 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 WhalesPorpoises (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 WhalesDolphins (family Delphinidae)

collectively referred to as delphinidscommon 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 WhalesDolphins (continued)

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

EcholocationEars are modified to receive a wide range of

underwater vibrationsEcholocation allows cetaceans to distinguish

and hone in on objects from distances of several hundred meters

Dolphins emit clicking soundsorientation clicks: low-frequency clicks that give the

animal a general idea of its surroundingsdiscrimination clicks: high-frequency clicks that

give the animal a precise picture of a particular object

EcholocationNo 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 melonmelon: 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

EcholocationEchoes provide 4 types of information:direction from which echo is comingchange in frequencyamplitudetime 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