Almost all dolphins live in the sea. There are a few which have adapted to the very different conditions found in rivers.
Think about some of the differences between the sea and rivers.
The sea is salt water, rivers are fresh water.
Rivers are often muddy making it very difficult to see. The waters near the surface of the sea are usually clearer with better visibility.
Rivers may be shallow and narrow. There may be much less space to swim and hunt in than at sea.
The River Dolphins
There are five types of River Dolphin.
The Boto is the Amazon River Dolphin. It lives in the Orinoco River as well as the Amazon.
The Indus and Ganges River Dolphins live in those rivers. They are almost identical.
The Baiji is the Chinese River Dolphin. It lives in the Yangtze River. This river is also called the Changjiang.
All these dolphins have similar adaptations to their environment.
They all have especially long beaks. This lets them search for fish in between the roots of trees along the river bank and to reach fish in the mud at the bottom of the river.
They have necks which are much more flexible than oceanic dolphins. They can move their heads from side to side so they can swim among roots and branches.
They have very good echolocation or sonar but poor eyesight. The Ganges and Indus
River Dolphins are blind. Good eyesight is of no use in murky waters. They use echolocation to build a sound picture of their environment.
The final member of the River Dolphin family is the Franciscana. It lives in very shallow seas along the coasts of Argentina and Brazil. It does not live in rivers!
Draw a map to show where the Baiji, Boto, Indus and Ganges River Dolphins live.
Name the rivers and the countries which they flow through.
Add the names of large cities such as Beijing and Shanghai in China, Madras and Delhi in India, Karachi in Pakistan, Caracas in Venezuela and Rio de Janeiro and Salvador in Brazil,
Complete your map with the names of the 7 Continents and 5 Oceans, the Equator, Tropics and Polar Circles.
Try to find pictures of River Dolphin in books or on CDROM. Draw diagrams to show how their bodies have adapted to their river habitat. Compare these adaptations to an “ordinary” dolphin such as the Bottlenose.