Oceanography and Environment (علوم البحار والبيئة)

OCEAN LIFE

OCEAN LIFE

Marine Mammals

Characteristics
Adaptation
Migration & Distribution

Ocean Life: Mammals -Characteristics

Mammals are a group of vertebrates (animals that have a backbone). Certain characteristics separate them from all other animals: mammals breathe air through lungs, give birth to live young, produce milk for their young, are warm-blooded, and have hair or fur. They also have relatively large brains and a variety of tooth sizes and shapes

Marine mammals have adapted to life in the ocean. More than 100 mammals depend on the ocean for most or all of their life needs. Marine mammals have all the characteristics of mammals, but they have different appearances and survival strategies



A group of walrus sun themselves on a beach-courtesy of NOAA



A manatee cow and calf-courtesy of NOAA

Marine mammals are divided into three orders: Carnivora, Sirenia and Cetacea. Within the order Carnivora are the pinnipeds (seals, sea lions, walruses), the sea otter, and the polar bear. Polar bears are closely related to bears like the grizzly, but are considered marine mammals since they have adopted a marine lifestyle. The order Sirenia is composed of manatees and dugongs (or sea cows), and the order Cetacea includes whales, dolphins, and porpoises

On the right is a picture of a humpback whale breaching, or jumping out of the water. Actually, this animal is feeding and has just taken a mouthful of fish, probably herring in southeast Alaska. The water drains out of the back of the mouth, leaving the fish behind to be swallowed. Breaching allows gravity to help drain the water



A humpback whale breaching -U.S. Navy photo


Ocean Life: Mammals -Adaptation

Thermoregulation

Marine mammals are well adapted to life in the water. Pinnipeds, sea otters and polar bears are amphibious (able to operate on land and in the water). Sirenians and cetaceans spend all their time in the water.

Keeping a constant body temperature is the most serious challenge facing warm-blooded mammals in an aquatic (watery) environment. Most marine mammals have an insulating layer of fat called blubber that keeps their bodies warm and buoyant. Blubber is rich in lipids (fats or fatty material that cannot dissolve in water) and stores large amounts of energy. Sea otters keep their body temperature constant with a dense (thick) layer of fur that traps a layer of air next to the skin so that their skin never gets wet. Polar bears and some pinnipeds have a thick layer of fur and a blubber layer

Another way marine mammals control their body temperature is by controlling their blood flow in a process called vasodilation. During vasodilation, blood flow increases to and from peripheral vessels near the surface of the flippers, flukes, and fins. Countercurrent heat exchange allows cold blood returning to the body core to be warmed up by exhanging heat with arteries going to the periphery- flukes and flippers



Two gray whales breath at the surface. The blowhole is made up of two slits -courtesty of NOAA

Diving

All marine mammals have special traits that allow them to dive deep and stay underwater for a long time. At some point, all must return to the surface to breathe. Whales and dolphins breathe through single or paired blowholes on the dorsal (back) surface of their head. At the surface, they quickly inhale and relax the muscular flap to close it so they can dive

When diving, blood is directed away from tissues that can handle low oxygen levels and toward the heart and brain where oxygen is needed most. During diving, the heartbeat slows down. Some champion divers are the sperm whales. They can dive more than 1600 meters (over a mile) and may remain submerged for an hour or more! Another champion diver, the elephant seal can dive more than 1500 meters (4920 feet) and stay under for two hours. Bottlenose dolphins can dive to depths of 540 meters (1770 feet) and remain underwater for 8-10 minutes



A striped dolphin breaths through a single blowhole -courtesy of SACLANT Center, La Spezia, Italy

Ocean Life: Mammals -Adaptation


Locomotion

Marine mammals have a streamlined shape for efficient movement through water. The lack of fur coat on several marine mammals is an important advantage to swimming; smooth skin creates less drag than fur does



The tail fluke of a sperm whale is used to move it through the water courtesy of SACLANT Center, La Spezia, Italy


Pinnipedia is a Latin word meaning "feather-footed" and refers to the flippers, which are shaped like wings or feathers. Although most of their lives are spent in the water, pinnipeds are also dependent on land for resting, giving birth, and breeding. Locomotion is one major difference between sea lions and seals. Sea lions use their forelimbs (hands) for locomotion on land and in the water. In the water, they use their forelimbs in a flapping manner similar to birds in flight. Seals use their hind limbs (feet) for swimming by undulating (moving from side to side) their hindquarters. On land, they move with vertical undulations of the trunk of the body



Dorsal fins of Risso Dolphins -courtesy of SACLANT Center, La Spezia, Italy

The hind limbs of sea otters are so much larger than the forelimbs that walking on land is clumsy and slow. Sea otters spend most of their time in the water floating on their backs and alternately pumping the hind flippers up and down. When a sea otter wants to swim faster it lies on its belly, undulating its entire body

When polar bears are on land, huge paws help distribute their weight while little hairs on their footpads increase friction between their feet and the ice. Polar bears can stay in the water for a long time and swim very well with a stroke like a crawl, pulling themselves through the water with their front legs while their hind legs trail behind

Ocean Life: Mammals -Adaptation

Food & Feeding

Cetaceans are near the top of the marine food chain and are classified into two groups: those with teeth and those with baleen. Baleen, which are large stiff plates that grow down from the gums of the whale's upper jaw, allow whales to filter feed. Baleen is made of keratin, the same protein that makes up hair and fingernails, and is strong, yet elastic. The whale filters (removes) plankton, krill, and small fish from seawater by squeezing water through the baleen with its tongue and then licking the plankton off the baleen. Toothed whales are hunters and use their teeth to grasp their prey, but do not chew their food. They eat fish, squid, and other marine mammals. To the left is an upside down picture of a beached right whale showing the long baleen plates that hang from the upper jaw. The fringes on the baleen work like a net to trap food but let water pass back out of the mouth



A whale's baleen plates -courtesy of Darlene Ketten WHOI

Manatees and dugongs are herbivores. They only eat vegetation, such as sea grasses, algae, mangrove leaves, and water hyacinths

Pinnipeds have teeth that are sharp and good for grabbing fish and other food such as shellfish. Like the toothed whales, pinnipeds do not chew their food, but swallow it whole or in big chunks. A polar bear's favorite food is seal. If there are no seals to hunt, they will eat small whales, lemmings, and even geese. On the right is a picture of a sea otter eating an octopus. Sea otters typically float on their backs while eating, using their chest as a dining table. A tool such as a stone is used to break open the hard shells of their prey (clams and crabs) or to knock shellfish off rocks. This is one of the few known cases of an animal using tools. The sea otters have flat molars for grinding and eat mostly benthic (bottom-dwelling) invertebrates (animals with no backbones), such as clams, mussels, urchins, crabs and abalone


Ocean Life: Mammals -Adaptation



The bottlenose dolphin (Tursiops) on the right camouflages with the water-Office of Naval Research photo

Camouflage

To blend into their environment, some marine mammals have countershading (their top side is darker that their underneath surfaces). This coloration, typical of many marine mammals, provides camouflage. The result is that predators or prey do not see a contrast between the animal and the environment because the top blends in with dark depths when viewed from above and the light belly blends in with the sunlit surface when seen from below. To the right is a picture of an hourglass dolphin illustrating the general pattern of dark upper dorsal coloration and light ventral (belly) coloration seen in many marine animals

Another example of camouflage is the coloring of the polar bear. The polar bear is white to blend in with its snowy environment. When sneaking up on prey, the polar bear will cover its black nose with its paw to blend in perfectly with its surroundings



Polar bears blend in with the snowy white environment. These bears will cover their black nose and eyes with their paw to blend -courtesy of NOAA

Sensory Systems

Pinnipeds have large eyes for seeing in the low light conditions often found underwater. In cetaceans, the eyes are located on the sides of the head, but focus forward. Both the pinniped's and cetacean's eyes are adapted to see well underwater. As a result, their in-air vision suffers. Manatees have small eyes and fair to poor eyesight. They seem to be farsighted and rely on touch to identify objects close up

Pinnipeds have small olfactory (sense of smell) lobes, and evidence shows that smell is important when interacting with other pinnipeds. Toothed whales do not have a sense of smell, but baleen whales do have some olfactory nerves. Cetaceans have taste buds at the base of their tongue, and the common dolphin and the bottlenose dolphin are able to distinguish (tell apart) certain smells. Manatees have a good sense of smell and are often selective in their food choices. Sirenians have many more taste buds than their cetacean cousins, and this may contribute to their choices of food. Polar bears have an acute sense of smell, and it is the most important sense for detecting prey on land. A polar bear can smell a seal more than 20 miles away



A young bearded seal pup -courtesy of NOAA


Ocean Life: Mammals -Adaptation

Communication

Marine mammals make and hear sound in different ways and for different reasons. The purpose of vocalizations ranges from communicating with the same species to locating unseen targets

Polar bears' hearing is as sensitive as human hearing. They make noise mostly when they are angry or threatened. Sounds include hissing, growling, champing of teeth, and soft chuffing. Cubs make noise by hissing, squalling, whimpering, lip smacking, and throaty rumblings. Polar bears also communicate through sight, touch, and smell. Sirenians have very small, hard-to-find ear openings. Their internal ear bones are very large and help provide a good sense of hearing. They communicate by making chirping, squeaking, and whistling noises

Pinnipeds make lots of different noises on land. Their sounds vary between sexes and ages. Sounds by breeding males are very loud, repetitive, and serve to threaten other males and advertise their high rank. Sounds can include barking, growling, yelping, and snarling. Female pinnipeds have a distinctive pup call, which helps a female recognize, locate, and maintain contact with her pup in crowded breeding colonies

COMMUNICATION

Cetaceans produce two types of sound: one is for communication with other cetaceans and the other is to help them explore their environment. Both are produced as air moves in and out of nasal sacs. The most famous use of sound for communication between cetaceans is the song of the humpback whale. Cetaceans can explore their environment and objects in it through the use of echolocation. Echolocation is done by of sending out pulses of ultrasonic (the frequency is too high to be heard by humans) sound through the blowhole. When the sound waves bounce off objects in their path, a portion of the signal is reflected back. Features of the returning echo offer information about distance, size, shape, texture and material composition of an object. This system of sensing the environment is an advantage in orientation, navigation, and capturing prey in dark or turbid waters


Ocean Life: Mammals -Migration & Distribution

Marine mammals are widely distributed throughout the ocean. Some migrate and inhabit many different waters while others confine themselves to one small area. Migration is a regular journey between one region and another, usually associated with seasonal changes or breeding and feeding cycles

Polar bears are found throughout the Arctic and the majority of them are found near land masses at the edge of the polar basin. Polar bears travel over the whole year within individual home ranges. Home range size depends on access to food, mates and dens. They also prefer to travel on sea ice; therefore, their ranges are limited by the amount of sea ice that forms in the winter



Pacific White-Sided Dolphins -Lagenorhynchus obliquidens



An aerial view of a mother bowhead whale and her calf -courtesy of NOAA

Sea otters are found along the Pacific Coast of the United States, Canada and Alaska

Pinnipeds and cetaceans make long-distance seasonal migrations to rookeries (breeding grounds) or warm-water birthing grounds. Reproduction and migration are often timed with seasonal changes in the availability of food for the adults and young. Many arctic pinnipeds migrate with the movement of food, but also with the seasonal movement of the ice pack

All living sirenians are found in warm tropical and subtropical waters. They migrate into warmer waters during the colder months of the year when the water temperature drops below about 68 degrees F (20 degrees C). Manatees are found in the warm waters of the West Indies, Florida peninsula and the Amazon Basin. Dugongs are found in the Indian and western Pacific Oceans, northern Australia and the Persian Gulf good luck for all  بالتوفيق للجميع  الموضوع منقول للامانه 
            Mohamed Hassaan
Oceanography

OCEANOGRAPHY and ENVIRONMENT

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نشرت فى 11 إبريل 2011 بواسطة Oceanography

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علوم البحار والبيئة Oceanography and Environment

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