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CETACEAN BASIC
Dolphins, whales and porpoises belong
to the group of marine mammals called Cetacean. Although they look
like fish, dolphins and whales are air-breathing mammals. They have
a hairless streamlined body, flippers and a tail with horizontal
flukes. But like fish, they cannot live out of water. Cetaceans are
the only mammals that spend their entire lives in water and include
whales, dolphins and porpoises.
Dolphins and whales must come to the surface at regular intervals to
breathe. If for any reason a cetacean is trapped under water it will
drown. The nostrils (blowhole) are located on top of their head.
When they come to the surface, they open their nostrils and exhale a
spout of moist air mixed with particles of water (blow).
Dolphins and whales are warm-blooded creatures, their body
temperatures being about that of humans. An insulating layer of
blubber beneath the skin helps to conserve heat. There are no
external ears. Cetaceans give birth to live young that are nourished
on the mother's milk.
What are cetaceans?
Cetaceans include all whales, dolphins and porpoise. They are marine
mammals.
Dolphins, whales and porpoises are among the largest and most
intelligent animals living on our planet. They live in oceans all
over the world. Some dolphins like the shushuk in Bangladesh live in
large rivers. Over 80 different kinds or species of dolphins, whales
and porpoises are found throughout the world. This group of animals
is known as cetaceans [sa-TAY-shuns].
How are cetaceans different from fish?
Cetaceans are NOT fish. They are mammals - just like us.
Mammals are air breathing animals. Most fish obtain oxygen from the
water through their gills. Mammal babies grow inside their mother's
womb and are born alive. Most fish leave their mother as eggs.
Female cetaceans, like all mammal mothers, give milk to their
babies. They take good care of their young until they can survive on
their own. Fish generally receive no food or care from their
parents.
The most obvious visible difference between cetaceans and fish is
their tail. Fish have a vertical tail which they move side to side.
Cetaceans have a horizontal tail or flukes which they move up and
down.
How are cetaceans different from other mammals?
Cetaceans are aquatic mammals. They spend their entire life in
water. Cetaceans come in many different shapes and sizes but they
share important features that allow them to feed and reproduce in
the water.
Baby cetaceans are known as calves. Calves are born with soft flukes
and fins. This makes it easier for them to slip out of their mother
at birth. They are usually born tail first so the blowhole comes out
last. This stops the calf from breathing in water. The mother gives
birth near the surface. This allows the calf to surface quickly to
take its first breath.
Calves can swim at birth. During the first few weeks of their lives
they stay close to their mothers for protection. Cetacean mothers
guard their calves against predators (animals that eat other
animals) such as sharks.
Mothers begin to feed their calves with milk a few hours after they
are born. The mammary glands that produce the milk are located near
the tail for easy access by the calf. The milk contains lots of fat
and comes out like soft cheese. This fat helps calves develop a
thick layer of blubber which keeps them warm.
How are dolphins, whales and porpoises different from each other?
Cetaceans are divided into two groups - those with teeth and those
without teeth. Toothed whales (Odontocetes [oh-don't-oh-seat-s]) are
predators that use their peg-like teeth to catch fish, squid, and
marine mammals. The sharp teeth help them catch their slippery prey
(the animals they hunt). Most toothed whales swallow their food
whole, without chewing it first. They have one blowhole (nostril)
and use echolocation to hunt. Toothed whales communicate with
high-frequency sound (clicks, whistles, squeaks, squawks). Toothed
whales tend to travel in highly organized groups with a social
hierarchy. The Odontocetes or toothed cetaceans include all the
dolphins and porpoises and beaked and sperm whales.
Baleen whales (Mysticetes [miss-ta-seat-s]) are large predators that
filter enormous amounts of small fish, shrimp-like creatures called
krill and tiny animals called zooplankton from the water. Instead of
teeth they have large, stiff bristles (baleen), which hang down from
their upper jaws. Mysticetes use their baleens to trap their food.
Baleen whales have two (paired) blowholes. Baleen whales tend to
grow and mature more rapidly than toothed whales.
Baleen whales produce low-frequency sound. Low-frequency sounds
travel long distances. Baleen whales are more solitary than
odontocetes and spread out, so communicative sounds need to travel
farther.
Most baleen whales are long-distance migrators. Baleen whales
undertake some of the longest migrations in the animal kingdom.
This group contains all the large whales, with the exception of the
sperm whale.
Dolphins and porpoises have different shaped teeth. Dolphin teeth
are shaped like a cone. Porpoise teeth are shaped like a spade.
River dolphins are only distantly related to marine dolphins and
have special adaptations that allow them to survive in the world's
largest rivers. River dolphins include our shushuk in the Padma,
Jamuna and Meghna Rivers.
Marine dolphins are less maneuverable but can swim much faster than
river dolphins. These animals often occur in large groups which
allow them to work together for catching prey.
How do cetaceans survive spending their entire life in water?
All animals need oxygen to live. Like people cetaceans get oxygen by
taking in air through their lungs. They must come to the water's
surface to breathe. If a cetacean is trapped underwater it will
drown.
Cetaceans breathe through blowholes on the top of their heads. This
means they can breathe without raising their heads far above the
surface.
Cetaceans usually surface to breathe every few minutes but some
large toothed whales can hold their breath for as long as an hour.
At the surface cetaceans open their blowholes and take as much air
as possible into their lungs. Before diving they close their
blowholes to stop any water from getting in.
Heat escapes much more quickly in water compared to air. A thick
layer of fat known as blubber helps cetaceans keep warm.
Cetaceans are amazing swimmers. Their tail flukes, smooth skin and
streamlined body help them move quickly through the water. They have
flippers on both sides for turning and balance.
Cetaceans never go completely to sleep. They sleep by "switching
off" half of their brain at a time. They need to keep the other half
of their brain switched on in order to breathe and to sense
predators.
Cetaceans have sensitive skin. They use touch to communicate.
Dolphins often show other dolphins they are friends by rubbing
bellies and flippers.
Most cetaceans have good eyesight. However to navigate, find each
other and catch fish toothed cetaceans rely mostly on a sense called
echolocation. They share this ability to see using sound with bats.
River dolphins have poor eyesight but exceptionally well developed
echolocation abilities. This allows them to survive in the muddy
waters of the rivers where they live.
What is echolocation?
Most cetaceans have good eyesight. But to navigate, find each other,
detect and catch their food toothed cetaceans rely mostly on sound.
Using sound to see is called echolocation [ecko-low-cay-shun].
The ability to echolocate is a great advantage to animals that live
in an environment where visibility is limited, like in our muddy
rivers.
Sound travels in invisible waves. Sound is carried much more
efficiently through water than through air.
Toothed cetaceans make high-pitched clicking sounds by forcing air
through small tubes located inside of their blowholes. These sounds
then pass through a fatty sac in their forehead that focuses the
clicks to where the animal wants to see. By scanning back and forth
the cetacean creates an image from the reflected sounds.
Toothed cetaceans become aware of their surroundings using
echolocation. They use echolocation to navigate, detect and capture
prey, monitor predators, and find and cooperate with members for
their own species for feeding and reproduction. In medical science
echolocation is called ultrasound and it used to examine the health
of human babies.
Baleen whales don't use echolocation because they don't have to hunt
their prey. They produce powerful low frequency sounds (songs) that
can travel over vast distances (sometimes over hundreds of miles).
The whale songs are used to communicate and attract mates.
What makes river dolphins special?
True river dolphins are only distantly related to marine dolphins.
They have very long snouts and small eyes. River dolphins have poor
eyesight because vision is almost useless in the muddy waters where
they live. Instead river dolphins have a highly-developed sense of
echolocation.
River dolphins are highly maneuverable with their large flippers and
flexible necks. Shushuks swim on their side finding their way by
touching the bottom with their large flippers.
River dolphins are not social animals and generally occur alone or
in small groups at river confluences or bends.
A few dolphin species occur in both rivers and the sea. One of these
is the Irrawaddy dolphin. The Irrawaddy dolphin lives in the
freshwater channels of Sundarbans mangrove forest and in coastal
waters of the Bay of Bengal. Irrawaddy dolphins occur far upstream
in some large rivers in Asia but not in the Jammuna-Padma-Meghna.
The reason might be due to competition from the shushuk - a true
riverine specialist..
What makes baleen whales special?
Baleen whales include the blue whale. This is largest creature to
ever roam the earth. Blue whales can grow to more than 30m long and
their heart is the same size as a tempo.
Baleen whales eat by taking enormous gulps of water with small fish,
shrimp-like creatures called krill and tiny animals called
zooplankton and straining out the food with their baleen as they
push the water back out with their tongue.
Baleen is a sieve-like device that helps Mysticeti (baleen whales)
catch very small prey in large amounts. Baleen grows from the roof
of the mouth (upper jaw) of baleen whales and hangs down in stiff,
flexible structures called plates. The baleen plates are composed of
keratin, just like our hair and fingernails. Baleen grows throughout
a whale's lifetime. Baleen is also called whalebone. It is flexible
and was used as a substitute before the invention of plastic. A
baleen whale feeds by filling its mouth with water that is packed
with fish and zooplankton. Then it closes its mouth and lifts its
tongue, forcing the water out through the baleen plates. The baleen
plates act like a sieve, letting out the water but trapping the food
in the whale's mouth. The whale then picks out the food with its
tongue and swallows it.
Baleen whales live mostly alone and far away from other members of
their species. They have special sites called breeding grounds where
they meet at the same time each year to find mates.
Baleen whales make the longest migrations of any animal. They travel
from summer feeding grounds in polar waters to winter breeding
grounds in the tropics. Some whale populations are resident to the
same location throughout the year.
When whales breathe they blow a cloud of spray above the water. This
blow is he whale's breath. It becomes visible when it hits the
cooler air. The blow also contains water that has been trapped
around the blowhole. By looking at the size and shape of the blow it
is sometimes possible to tell what kind of whale made it.
Baleen whales are not believed to echolocate. However scientists
believe they communicate over long distances with low pitched songs.
Sound travels much better in water compared to air. Whale songs have
been recorded by underwater microphones more than 1000 kilometers
away from the animals.
What makes marine dolphins special?
Marine dolphins are fast swimmers. Dolphins that live far out at sea
sometimes occur in groups of thousands. Marine dolphins often catch
fish by cooperating together to herd them into a dense mass. This
way they can more easily catch them with their sharp teeth.
Marine dolphins are social animals. In some species the elder
females are the leaders.
Marine dolphins are often seen rubbing against each other in social
play. Males sometimes ram into each other while fighting over
females.
There are more species of marine dolphin than other kind of
cetaceans. Some marine dolphin species are found only in small areas
while others range throughout the worlds oceans.
What cetaceans occur in Bangladesh?
Local and international scientists recognize Bangladesh as a global
"hotspot" for cetacean diversity and abundance. This means that the
rivers and coastal waters of the country support a large variety of
different species and that the populations are healthy when compared
to neighboring countries in Asia.
The most well known dolphin in Bangladesh is the shushuk. Shushuks
are true river dolphins. They are strange looking animals with an
extraordinary long snout, a tiny dorsal fin and large flippers.
Shushuks live throughout the Jamuna, Padma and Meghna Rivers and are
frequently seen at ferry crossings.
Irrawaddy dolphins are found in rivers and in coastal waters that
receive freshwater from rivers. They shares habitat (the place where
they live) with the shushuks in the waterways of the Sundarban
mangrove forest.
Indo-Pacific humpback dolphins and finless porpoises are occasional
visitors to the mangrove forest but they live mostly in open coastal
waters that receive freshwater flows from the Jamuna, Padma and
Meghna Rivers
Indo-Pacific bottlenose, spinner and pan-tropical spotted dolphins,
and breeding populations of Bryde's and fin whales live in a
deep-sea canyon called the Swatch-of-No-Ground. This canyon descends
to more than 900 meters and is located only forty kilometers from
the Sundarban mangrove forest.
Bangladesh supports an extraordinary variety of cetaceans in a small
area of mangrove forest, coastal and deep-sea canyon waters. Our
challenge is to protect these amazing animals from extinction.
Why are some cetaceans threatened with extinction?
Cetaceans face many threats from humans. Thousands of cetaceans die
each year when they become entangled and drown in fishing nets. The
widespread use of mosquito nets for catching shrimp fry has depleted
populations of fish prey. Pollution from pesticides and industrial
waste make cetaceans sick and reduce their resistance to disease.
River dolphins are particularly endangered because people are
draining the rivers where they live and dams have isolated groups
from coming together to reproduce.
Why are people interested to save cetaceans from extinction?
Dolphins, whales and porpoises are fundamental to life in rivers and
the sea. They are symbols of the need to take good care of aquatic
resources that also essential to the survival of human communities.
Cetaceans and humans need clean water and healthy fish populations.
Cetaceans are endearing to local Islamic and Hindu cultures and are
the fishermen's companions at sea and on the river. Humans have been
long been fascinated by cetaceans and there are many stories of
dolphins protecting people from shark attacks or rescuing people at
sea.
Many people are interested in dolphins because they appear to be
very intelligent. Dolphins have large brains, are good at solving
problems. They even recognize themselves in a mirror. Some people
believe that dolphins have their own language
What can I do to help dolphins, whales and porpoises?
Being well informed is the first step. By visiting this webpage and
reading about dolphins, whales and porpoises you are already helping
to save cetaceans. When decisions are made by your family and
friends to take actions that might endanger cetaceans you have a
responsibility to speak out for these animals. Tell others about
what you know and ask them to join you in protecting cetaceans.
These animals are part of the rich wildlife heritage of Bangladesh.
Many dolphins die from entanglement in fishing nets and lines.
Encourage fishermen not set 'current jahls' in areas where they see
dolphins and to stay with their nets. If a dolphin gets caught its
life can be saved by quickly pulling the animal to the surface and
setting it free. The net may have to be cut. It can be repaired but
a dead shushuk is gone forever.
If you find a live cetacean stranded on the beach get it back into
the water as fast as possible. Make sure to keep the cetacean cool
and wet. Do not touch, cover or splash water on its blowhole. A
simple carrier can be made from a lunghi for transporting a dolphin
or porpoise back to the water.
Never attempt to catch a shushuk or keep it in a pond. It will not
survive.
Information from dead cetaceans is valuable to help others survive.
If you find a dead cetacean make sure it does not wash away or get
eaten by scavengers. Inform the BCDP Dolphin Team as soon as
possible. We will keep your name anonymous.
Cetaceans are protected by law. It is illegal to catch these animals
or to sell or buy the whole animal or any parts of it.
To learn more about dolphins, whales and porpoises in Bangladesh
brows through this website, ask you local school teacher or call the
BCDP Dolphin Hotline.
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