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 best known dolphin in Bangladesh is the shushuk, or Ganges River dolphin. 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 share their 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 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.