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Chapter 12Chapter 12Marine MammalsMarine Mammals

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 retain their young inside their body until they are ready to be born

Sea Otters• Sea Otters (Enhydra lutris; order Carnivora)• 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

• vocal and playful• Nearly hunted to extinction for fur

Polar Bears• Polar Bears (Ursus maritimus; order Carnivora)• 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

Polar Bears• Diet consists primarily of seals• 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• 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 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• Gestation = approximately 1 year• 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 eats penguins, sea birds and other seals

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• 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• 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.

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

• 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

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

• 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

General Characteristics of Cetaceans

– 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

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 Diving• Lungs are smaller in proportion to their body size

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– 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– can hold breath without urge to breathe

• Large amounts of hemoglobin and myoglobin

Adaptations for Diving

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– 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

Cetacean Behaviors

• Slapping – 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 Behaviors

• Slapping (continued)– tail slashing and tail swishing: moving the tail

from side to side across the surface of the water to create turbulence

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• 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

• 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

Whale ascends in a spiral pattern blowing bubbles from its blowhole

Bubbles

Krill

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• Rorquals (family Balenopteridae)

– 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

Baleen Whales

• Rorquals (family Balenopteridae) (continued)– 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)– 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, 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)– 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 warm-blooded 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• 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

Echolocation

• Echoes provide 4 types of information:– 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