Saturday, January 7, 2012

oceanography - ocean life

Ocean Life: Mammals -Characteristics

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Text Box:  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.
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.
Photo of a two manatees at the water's surface   Photo of a humback whale jumping out of water

Ocean Life: Mammals -Adaptation

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

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.Text Box:  
A striped dolphin breaths
through a single blowhole

 

 

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.
Text Box:  
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.
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.Text Box:  
Dorsal fins of Risso Dolphins
(courtesy of SACLANT Center, La Spezia, Italy).


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.

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.Text Box:

Ocean Life: Mammals -Adaptation

Camouflage

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

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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)
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.








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!

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.

 

  

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


Text Box:  
Pacific White-Sided Dolphins
(Lagenorhynchus obliquidens)
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.
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.Text Box:  
An aerial view of a mother
bowhead whale and her calf
(courtesy of NOAA)


Ocean Life: Quick Quiz

1. Camouflage helps marine mammals attract mates.
True
False

2. Why is the Green Sea Turtle's skin green?
Green is prettier than blue.
Because of the algae and grass they eat.
It keeps them warmer.
Reptiles are always green.

3. Myrtle the Turtle is helping scientists understand how turtles hear.
True
False

4. What is breaching?
A baby blue whale.
A whale scare tactic.
A mating dance.
A whale feeding behavior.

5. Where do sea turtles lay their eggs?
On a nesting or natal beach.
On shipwrecks.
On their backs.
In seagrass.

6. Marine mammals are only found in the Arctic.
True
False

7. What is baleen?
Turtle shells.
Large stiff plates that grow down from the gums of a whale's upper jaw.
Whale tails.
Penguin nesting grounds.

8. Blubber keeps marine mammals warm and buoyant.
True
False

















































Ocean Life: California Sea Lion - Characteristics


There are 34 species of Pinnipeds, the "wing" or "fin-footed" mammals, which include 14 species of eared seals. The California sea lion belongs to the family Otariidae which means "little ears". There are two geographically separate subspecies of California sea lion recognized: Zalophus californianus californianus, which is found off the west coast of North America, and Zalophus californianus wollebaeki, which lives in the Galapagos Islands in the Central Pacific Ocean. A third subspecies, Zalophus californianus japonicus once lived near Japan but is now thought to be extinct. In the scientific community, there are many debates concerning the ancestry of eared seals. It is believed that eared seals and walrus' descended from a bear-like ancestor that returned to the sea 30 million years ago in the North Pacific.

Appearance

The California sea lion is the playful, noisy, exuberant, quick learning,"trained seal" of the circus and zoo. It has a streamlined body, a thick layer of blubber and short, thick fur with typical coloring ranges from tan to chocolate brown and may appear black when wet. Males, bulls, are darker and bigger than females. Males may reach 1,000 lbs. (more often 850 lbs., or 390 kg) and 7 feet (2.1 m) in length. Females, cows, are considerably smaller and grow to 220 lbs. (110 kg) and up to 6 feet (1.8 m) in length. Pups are about 75 cm long and weigh 13-20 lbs. (6-9 kg). The head has a pointed muzzle and the profile resembles that of a dog.













Ocean Life: California Sea Lion - Adaptation


Thermoregulation

Sea lions are often seen floating with one or more flippers extended out of the water. They do this to regulate their body temperature. The sun warms the blood in their dry flippers and the heat is then transferred to the rest of the body. To cool down, they dip their flipper into the water and then raise it back up into the air, a behavior that results in lowering the blood temperature through evaporative cooling.

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A California sea lion under water
(courtesy of Dan Costa, UCSC)
Locomotion

Sea lions are adapted for movement on land as well as in the water. Wing-like front flippers have bone structure similar to that in our arms and hands. They swim by making long simultaneous sweeps with their front flippers, "flying" though the water. When on land, they are able to rotate their hind flippers underneath their body and use all four flippers to walk. Sea lions are fast swimmers and can swim in burst speeds up to 25-30 knots (30mph), but generally cruise at about 5-15 knots (11mph). Sea lions gain speed by porpoising, leaping clear of the water and then gliding near the water's surface to minimize resistance.

Diving

Sea lions have been recorded diving to a maximum depth of 125 feet (375m) and can be underwater for an average of 2-8 minutes, diving with at least partially inflated lungs. Sea lions are able to dive so deep and stay under water so long because they have a high tolerance for carbon dioxide and the oxygen in their body is shunted (diverted) to the heart and central nervous system rather than on non-vital organs.








Ocean Life: California Sea Lion - Adaptation


Feeding

Not much is known about the feeding habits of the California sea lion. Sea lions are an opportunistic feeder, eating what is available. They are carnivores (animals who eat other animals) and eat fish, squid, octopi, crabs, clams, and lobsters. Their diet includes several fish species, such as anchovy, whiting and herring. Sea lions will eat 5-8% (15-35 pounds) of their body weight daily. They have 34-38 cone-shaped teeth that are specially designed for grasping slippery fish; however, sea lions do not chew their food, but swallow it whole or in large chunks. Most of their water intake comes directly from the fish they eat although they may drink small portions of sea water while fasting throughout the breeding season. Strangely, rocks have been found in the stomachs of sea lions. The exact reason is unknown, but one theory states that sea lions may swallow rocks to create a false sensation of feeling full during the period when they fast.

Senses

Text Box:  
Rocky, a trained Navy sea lion, shows off
his features that aid him with hearing,
smell, sight and touch
(courtesy of Dan Costa, UCSC)
California sea lions hear well both above and below the water’s surface. Studies have shown that sea lions can hear frequencies as low as 100 Hz and as high as 40,000 Hz, while humans have a hearing range of 20-20,000 Hz. Sea lions vocalize within a range of 100 to 10,000 Hz. Sea lions are very vocal and can bark, click, growl, squeak, and honk. Barking by male sea lions is related to social dominance, territorial defense, and alarm calling.

Sea lions cannot smell underwater, but above water their smell sense is highly developed. Females can recognize their pups by their distinctive scent and males use their sense of smell to recognize females in estrous during the breeding season. Mothers locate their pups on crowded rookeries through smell, sight, and distinctive vocalizations. Pups also learn to recognize and respond to the vocalizations of their mothers.
Sea lions have large eyes and excellent sight. Unlike humans, sea lions probably do not see in color. It is possible they can see colors in the blue-green spectrum. All pinnipeds have a membrane at the back of their eyes called a tapetum lucidum to aid in foraging while diving below the sunlit surface where there is little available light. Cats also have a tapetum lucidum and this is why the eyes of both cats and sea lions appear to glow at night. On land, their eyes are protected by a nicitating membrane, which wipes away sand and debris.
Sea lions are tactile mammals. Vibrissae, or whiskers, are stiff, thick hairs made of keratin (human fingernails are also made of keratin). These whiskers are found around the muzzle and are embedded in facial tissue rich in nerves and muscle fibers. This sensitive system functions to detect vibrations from sound or prey in the water and can be used to feel the shape and size of objects on land.








































Ocean Life: California Sea Lion - Adaptation


Breeding

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Stellar sea lions gather on the
beach to breed every year
(Office of Naval Research photo)
Female California sea lions begin to breed at 3 or 4 years of age. Males generally start to breed later, at about 8 years of age. During the annual breeding season, which occurs from May to July, a large number of individuals will congregate on an island or beach to give birth and mate. These breeding places are called rookeries. Males arriving on the rookeries will challenge and fight other males in order to establish a territory near the shore.
Once a territory is established, the bull remains to protect it, going as long as a month without eating and mating with as many females as possible. Only the largest and most dominant males have the opportunity to breed. A full-grown breeding male will have a sagittal crest, a raised forehead, that appears at about 5 years of age and fully developed by the age of 8.




Text Box:  
This adult male sea lion has a
sagittal crest, which lightens
with age
(courtesy of Schusterman
Long Marine Laboratory, UCSC)
Adult females give birth and mate once a year during the annual breeding season. Once the egg is fertilized inside the female, the development of the embryo can be suspended. This delayed implantation may last up to 3 months. Because the average gestation period is approximately 9 months in California sea lions, this pause in development allows females to give birth and breed at the same time every 12 months. Sea lions will mate about 10 days after the birth of their pup. Females will give birth to a single pup. Twins are rare and mothers rarely adopt other pups.
Pups are born in June and July with their eyes open and the ability to vocalize. They appear to be able to swim at birth, although their movements are not well coordinated. Pups nurse at least 5-6 months. Sea lion milk contains about 35% fat, so the pups grow rapidly. After about two months, the pups will supplement their diet with fish that they catch while swimming near the shore with their mothers. Between nursing intervals, the mother leaves the pup in the crowded rookery as she searches for food in the ocean. When she returns, the mother emits a distinctive loud call, which elicits a distinctive bleating response from her pup. This exchange of individually unique calls continues until mother and pup find each other. She makes her final identification by smelling her own pup.


Text Box:  
A sea lion mother and pup sun
themselves on the beach (Dan Costa,ONR)
Once the breeding season is over, the males will seasonally migrate long distances north while the females typically do not move beyond the Southern California Channel Islands. The males will then return to the breeding grounds to establish their territories.

































Ocean Life: California Sea Lion - Adaptation


Lifespan

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Steller sea lions gathering on a rocky shore.
The average lifespan of a wild sea lion is around 20 years, but some captive California sea lions have lived into their thirties, with females typically living longer lives than males. The age of a sea lion can be determined by counting the growth layers in their teeth, similar to counting rings in a tree trunk; however, this can only be done by removal of a tooth, so the exact age of many sea lions is not known.

Habitat

The California sea lion lives in cool waters and inhabits rocky and sandy beaches of coastal islands and mainland shorelines. They are highly adaptable to different surroundings and use a variety of habitats. These intelligent and social animals congregate in large groups on land, colonies, and smaller groups in the water, rafts. When resting on rocks or beaches they may lean back and point their noses skyward or they may be seen lying atop one another. When at sea they raft together, playing and leaping clear of the surface. California sea lions compete with Steller sea lions for both habitat and food in the area where their ranges overlap.

Distribution & Population

Each subspecies has its own range. The California sea lion, Zalophus californianus californianus, population estimate is between 161,066 and 181,355 and is increasing at a rate of about 5% a year. They range from the West coast of Mexico to British Colombia. They breed mainly on offshore islands from southern California's Channel Islands south to Mexico, although a few pups have been born on Año Nuevo and the Farallon Islands in central California. The Galapagos sea lion, Zalophus californianus wollebaeki, population estimate is 75,000 and live exclusively on the Galapagos Islands. The Japanese sea lion, Zalophus californianus japonicus once lived along the Sea of Japan, but is now probably extinct.






Ocean Life: California Sea Lion - Status & Threats


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An example of how net filaments can be harmful to sea lions. (courtesy of Schusterman, Long Marine Laboratory, UCSC).
The California sea lion is a protected species throughout its range, but the population continues to flourish despite ongoing conflicts with commercial and sport fisheries for species such as anchovy and herring. Sea lions are known to damage fishing gear and steal or destroy fish in the nets. As a result some California sea lions are illegally shot or drown in the nets. Some animals manage to escape from gill nets, but many of these animals are left with small pieces of net filament around their necks. These fragments of nets and other pieces of plastic debris eventually kills many sea lions by cutting deep into tissue as the animals grow around the constricting material. The increase of environmental toxins may also have a negative effect on sea lion populations.




Sea lions are occasionally preyed upon by killer whales, great white, hammerhead, and blue sharks. They are also known to have such diseases as pneumonia, caused by a parasitic lungworm, and a bacterial infection called leptospirosis, which affects their livers and kidneysText Box:  
A sea lion with a net filament wrapped around its neck
(courtesy of Schusterman, Long Marine Laboratory, UCSC)















Ocean Life: California Sea Lion - Current Research


Text Box:  
Rio, a trained Navy sea lion,
performs a cognition experiment
(courtesy of Schusterman, Long Marine Laboratory, UCSC).
The only lab in the world dedicated to the study of the sensory systems and learning abilities of pinnipeds is located at Long Marine Laboratory, in Santa Cruz, California. Dr. Ronald Schusterman and his crew of students and researchers are investigating the comparative abilities of three pinniped species, including the California sea lion. Research efforts with the lab’s two trained sea lions, Rocky and Rio, include assessment of their visual and auditory abilities. These behavioral tests are conducted in air as well as under water to determine how the senses of sea lions have evolved to cope with an amphibious lifestyle. For example, these studies support the idea that sea lions rely on vision to find food, and on hearing to avoid predators at sea and to communicate with one another on land.

One of the main goals of the research is to understand how underwater noise produced by humans (from sources such as shipping, oil drilling, oceanographic experiments, and military operations) might affect the hearing and behavior of wild California sea lions. The researchers approach this problem by asking the sea lions to detect sounds either following or during exposure to moderate levels of noise; this information is then used to estimate how different sounds might interfere with the sea lions’ ability to hear. Other experiments are designed to investigate how trained California sea lions use information gathered from their senses to solve problems related to learning and memory. All of these laboratory studies aid in understanding the natural behavior of wild sea lions. Ongoing field observations explore how sea lions use sensory cues to recognize individuals and to classify them into such categories as "potential mates," "territorial neighbors,"or "invading strangers."Text Box:  
Wearing headphones, Rocky is taking a hearing test (courtesy of Schusterman, Long Marine Laboratory, USCS).




Ocean Life: Green Sea Turtle - Characteristics


Name

Green Sea Turtles get their name from the color of their body fat, which is green from the algae or grasses they eat. The Hawaiian Green Sea Turtle population, is known by its Hawaiian name Honu.

History

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Green Sea Turtles are reptiles whose ancestors evolved on land and returned to the sea to live. The first turtles appeared during the Triassic period, 245 to 208 million years ago. Fossils for the earliest known sea turtles appear in the Late Jurassic period, 208 to 144 million years ago. Turtles are one of the few species that watched the dinosaurs evolve and become extinct.
As reptiles, sea turtles possess the following traits:
  • They are cold-blooded, meaning they get their body heat from the environment.
  • They breathe air.
  • Their skin is scale

Status

Now, scientists recognize seven species of these marine reptiles. The recognized sea turtle species are as follows: Greens, Hawksbill, Kemp's Ridley, Olive Ridley, Loggerhead, Flatback and Leatherback. The Loggerhead Sea Turtle is listed as threatened, the Flatback is listed as vulnerable, and all other species are listed as endangered. Green Sea Turtle populations of Hawaii are threatened and protected in Hawaii under state law. Populations of Green Sea Turtles off the coast of Florida and the Pacific coast of Mexico are listed as endangered. Green Sea Turtles are protected by the federal Endangered Species Act, and listed under the Convention on International Trade of Endangered Species (CITES). CITES makes it illegal to import or export turtle products.

Shell

In addition to their reptilian traits, all species of turtles except the Leatherback have evolved a bony outer shell, which protects them from predators. The Leatherback is the only soft-shelled sea turtle and is in a family by itself. The shell covers the dorsal (back) and ventral (belly) surfaces of a sea turtle. The dorsal portion of the shell is the carapace and is covered with scale-like structures called scutes, while the ventral portion of the shell is known as the plastron. Experts can identify species of sea turtles by the number and pattern of scutes on the carapace. The shell is considered the most highly developed protective armor of any vertebrate species. While most land turtles can retract their heads into their shells for added protection, sea turtles cannot and their heads remain out at all times.

Color

Green Sea Turtles have green flesh. The carapace is olive brown to black, while the plastron is pale yellow to creamy white. The carapace is molted, variegated in color. Rarely will you find a Green Sea Turtle with a solid colored shell. Counter-shading of the shell conceals the turtle from predators, making it difficult to distinguish the dark carapace from the sea floor and the light plastron from the lighter sky.

Size

Green Sea Turtles as hatchlings weigh about an ounce and have a carapace length of 2 inches. A sexually mature green sea turtle weighs 200-350 pounds with a carapace length of 2.5 feet. Adults grow to a carapace length of 3.5 feet and weigh an average of 400 pounds. One of the largest turtles that ever lived from the Late Cretaceaus period, 144 to 65 million years ago, reached a length of 9.8-13 feet.

Lifespan

The lifespan of sea turtles is not known. It is believed that Green Sea Turtles reach sexual maturity around the age of 25 years and can live up to 80 years of age. The long period of maturation helps to explain why it takes turtles so many years to recover from a population decline.

Shape

Sea turtles are wonderfully adapted to life in the ocean. Their shells are lighter and more streamlined than land turtles. Front and rear limbs have evolved into flippers. These flippers make sea turtles efficient and graceful swimmers, capable of swimming long distances in a short time.









Ocean Life: Green Sea Turtle - Adaptation

Speed & Diving

With their efficient body shape, Green Sea Turtles have been known to move through the water as fast as 35mph. When active, sea turtles swim to the surface to breathe every few minutes. When sleeping or resting, adult sea turtles can remain underwater for more than 2 hours. Turtles are capable of containing higher concentrations of carbon dioxide in their blood than most other breathing animals. This enables them to use their oxygen more efficiently and stay underwater longer. Juvenile sea turtles have not developed this ability and must sleep afloat at the water's surface.

Feeding

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Green Sea Turtle
(courtesy of Kathy Streeter, New England Aquarium)
Juvenile Green Sea Turtles are omnivorous, eating plants and animals. Their diet consists of jellyfish, shrimp, plankton and algae. Adult Green Sea Turtles are primarily herbivores, eating only plants, but they have been observed eating jellyfish and other easy-to-catch marine life. They feed on nearshore sea grass and algae pastures. Similar to cows, Green Sea Turtles depend on bacteria in their guts for digestion of plant material.

Distribution and Habitat

Green Sea Turtles are distributed throughout the world's oceans between 35 degrees north and south latitude. They are found in the eastern and western hemispheres and nest on beaches throughout the Atlantic, Pacific and Indian Oceans. Green Sea Turtles enjoy warm, tropical and subtropical, shallow water near continental coasts and around islands where the sea grass is plentiful.

Population

There were once several million Green Sea Turtles worldwide. Today, fewer than 200,000 nesting females are thought to remain. In Hawaii in 1992, the estimate of mature female green turtles associated with the French Frigate Shoals was set at roughly 750.



Ocean Life: Green Sea Turtle - Adaptation

Reproduction

Although Green Sea Turtles live most of their life in the ocean, adult females must return to land to lay their eggs. Upon sexual maturity, the Green Sea Turtle makes an amazing journey every two or three years to nest. They leave their feeding grounds and migrate as far as 800 miles to their nesting beaches. Biologists believe that nesting female turtles return to the same beach where they were born. This beach is called a natal beach. Males do not accompany the females, but they congregate at the breeding grounds. The males will mate with the females off the shores of the nesting beaches. The most popular nesting beaches are on French Frigate Shoals, where 90% of the Hawaiian population of Green Sea Turtles mate and lay their eggs.

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Green Sea Turtles
(courtesy of Kathy Streeter, New England Aquarium)
Green Sea Turtles nest only at night. After 7-10 weeks gestation period, the females pull themselves out of the water to the dry sand of the upper beach. Here, she uses her front flippers to dig a broad pit and her rear flippers to excavate an egg chamber. She then lays her clutch, which consists of 100-120 ping-pong sized, leathery-skinned eggs, in the egg chamber and carefully covers them with sand. Females lay up to five or six clutches of eggs in a breeding season. Once she buries the pit and disguises the location, her parenting job is complete. She returns to sea leaving her young to fend for themselves.
Hatching occurs at night and begins in July after about 60 days of incubation. Studies indicate that the temperature of the eggs during incubation influences the sex of the baby sea turtles. At 82 degrees F, hatchlings are male. At 90 degrees F, hatchlings are female. Baby sea turtles are able to chip through the eggshell with a structure called an egg tooth, a temporary hard protuberance on their beaks. Working as a group, the hatchlings dig to the surface of the nest and instantly head to the water, attracted to the moon's light reflecting on the ocean's surface. Therefore, artifical lights on nesting beaches can confuse the hatchlings and cause them to lose their way. Sharks, reef fish, birds and mammals all pose predator threats upon hatchlings. Once they reach the ocean, the hatchlings remain at sea until they appear as juveniles in the near-shore waters. Only 1 or 2 out of 100 hatchlings will survive the first year.

Predators

With their efficient mobility in the water and their size, adult Green Sea Turtles have only two known predators: sharks and man. Tiger sharks feed regularly on Green Sea Turtles. Man has been the greatest predator of the sea turtle, killing it for its meat, shell, and eggs while driving it almost to extinction.

Other Threats

There are many threats to Green Sea Turtles beyond that of predators. Entanglement in commercial shrimp nets trap and drown more than 10,000 sea turtles each year. Litter and other marine debris can be deadly when they entangle the turtles or are mistaken for food and ingested. Nesting grounds are lost each year to coastal development, leaving females without a familiar place to lay their eggs. Noise, lights and beach obstructions disrupt nesting areas and threaten this critical part of the sea turtle's life cycle. The recent presence of a disease called fibropapilloma has affected Green Sea Turtle populations in Hawaii as well as Florida. Fibropapilloma causes the growth of large tumors on the soft tissue of the turtles. The exact cause of the disease is not known. Scientist suspect that a virus, parasite or the effect of marine pollution may be involved.

































Ocean Life: Green Sea Turtle - Current Research

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Green Sea Turtles
(courtesy of Kathy Streeter, New England Aquarium)
Sea turtles are found in waters all over the world, offshore as well as inshore. As a result they are likely to be exposed to a variety of man-made sounds. Although all species of sea turtles are threatened or endangered, there is little known about the hearing capabilities of sea turtles or how they are impacted by sound. Until now, the information available was based solely on physiological tests. However, there is a behavioral study in progress at the New England Aquarium with a Green Sea Turtle (Chelonia mydas) named Myrtle. The hearing capabilities of this turtle are being investigated using psychophysical methods, standard operant conditioning techniques, and positive reinforcement schedules commonly used with marine mammals. This effort is funded by the Office of Naval Research and is conducted in collaboration with the University of Maryland, College Park, Maryland.
Myrtle is approximately 60 years old. She is housed in the New England Aquarium's landmark coral reef exhibit along with 700 fish and two other turtles. Despite the challenges related to working with a turtle and the distractions inherent to working with an individual animal in an exhibit environment, a training protocol and an experimental design have been developed making it possible to test Myrtle's hearing capabilities.
Since Myrtle was responsive to standard training techniques, she learned the basic behaviors required to test a variety of experimental designs and apparatus. Ultimately a Go/No-Go paradigm proved to be the one that Myrtle responded to most consistently and with a minimum of difficulty. She was not required to maintain a specific station position throughout a session. It was clearly difficult for her to do so. Instead, she had to initiate a trial by swimming to and touching a light box. This triggered a light, and sometimes a sound, to go on - indicating the start of a trial. Myrtle learned to touch the light again in the absence of a tone and to indicate that a tone was detected by swimming to and touching an under water response paddle. She was rewarded with fish, shrimp, crabs, vegetarian gel cubes, or lettuce for each correct response. A shield was dropped in front of the light after each trial to indicate the end of a trial.
Incorrect responses were not rewarded. The shield was simply raised again encouraging her to initiate a new trial. The preliminary data indicates that Myrtle hears tones ranging from 100Hz to 500Hz. Studies indicate that at 200hz her threshold is between 107dB and 119dB, and at 400Hz threshold is between 121dB and 131dB. These results are invaluable in that they represent the first and only behavioral data available on the range of sea turtle hearing capabilities. However the data should be interpreted cautiously because of Myrtle's age. It is reasonable to predict that younger turtles probably have a slightly wider bandwidth and are able to hear lower intensity sounds than Myrtle. Plans for the future include completing Myrtle's audiogram, studying masking thresholds, critical bands, critical ratios, and directional hearing capabilities.
















































Ocean Life: Quick Quiz

1. Camouflage helps marine mammals attract mates.
True
False

2. Why is the Green Sea Turtle's skin green?
Green is prettier than blue.
Because of the algae and grass they eat.
It keeps them warmer.
Reptiles are always green.

3. Myrtle the Turtle is helping scientists understand how turtles hear.
True
False

4. What is breaching?
A baby blue whale.
A whale scare tactic.
A mating dance.
A whale feeding behavior.

5. Where do sea turtles lay their eggs?
On a nesting or natal beach.
On shipwrecks.
On their backs.
In seagrass.

6. Marine mammals are only found in the Arctic.
True
False

7. What is baleen?
Turtle shells.
Large stiff plates that grow down from the gums of a whale's upper jaw.
Whale tails.
Penguin nesting grounds.

8. Blubber keeps marine mammals warm and buoyant.
True
False





















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