Ocean Life: Mammals -Characteristics
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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.
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.
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.
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.
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.
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.
Ocean Life: Mammals -Adaptation
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.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
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.
Ocean Life: Quick Quiz |
|
1. Camouflage helps marine mammals
attract mates.
|
2. Why is the Green Sea
Turtle's skin green?
|
3. Myrtle the Turtle is helping
scientists understand how turtles hear.
|
4. What is breaching?
|
5. Where do sea turtles lay their
eggs?
|
6. Marine mammals are only found in
the Arctic.
|
7. What is baleen?
|
8. Blubber
keeps marine mammals warm and buoyant.
|
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.
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
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
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.
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.
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
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
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 kidneys
Ocean Life: California Sea Lion - Current Research
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."
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
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
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.
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
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 |
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1. Camouflage helps marine mammals
attract mates.
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2. Why is the Green Sea
Turtle's skin green?
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3. Myrtle the Turtle is helping
scientists understand how turtles hear.
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4. What is breaching?
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5. Where do sea turtles lay their
eggs?
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6. Marine mammals are only found in
the Arctic.
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7. What is baleen?
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8. Blubber
keeps marine mammals warm and buoyant.
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