River dolphins are known to thrive in fresh water contrary to any people’s perception of dolphin’s habitat. They are generally of four species that vary in size depending on their residence. Some are known to grow up to 8 feet long. However, most of them are smaller in size. The variation is not just in size but also in color and this not mistake one species for the other but also mistakes the dolphins for other aquatic life. The river dolphins are commonly fond of the blackish and coastal regions of major rivers among them being the Amazon, gangez, the Indus, Yangtze and Mekong.
Baiji of Yangtze Dolphin
Among these types of river dolphins is the Baiji or Yangtze dolphin. It was found in the Yangtze River in China and was declared effectively extinct in 2007. It is still possible that members of this species do still live on though.
Their extinction can not be associated to any active hunt for the dolphins but increased fishing has contributed to the decline. The baiji breed in the first months of the year especially between February and April. They have a 30% pregnancy rate and a gestation that lasts 10-11 months.
The males are known to reach their sexuality at the age of four years while the females reach at the age of six. They weigh between 135 and 230 kilograms and the males are about 2.3meters and females 2.5 meters. They generally have an estimated lifespan of 24 years in the wild.
Indus River Dolphin
Another species is the Indus river dolphin. This is found in the Indus River and its tributaries such as Beas and Sutlej of Pakistan. They are known to occupy about 3400 km of the river but the distribution has recently declined to only a fifth of this. The Indus dolphin’s species are characterized by long pointed noses. Their teeth are visible both in the lower and upper jaws even with their mouth closed. The species is effectively blind as it does not have a crystalline eye lens. It uses echolocation to hunt and navigate in the rivers. Their bodies are usually brownish and stocky at the middle. More to this, they have large and thin flippers. The dolphin’s existence has adversely been affected by human beings. This is by use of the river systems and entanglement of the dolphins in fishing nets. This together with reduced levels of water due to irrigation has affected the population of Indus dolphins.
Ganges River Dolphin
The Ganges river dolphin, which existed in large schools near to urban places in Brahmaputra and Ganges rivers, is another species. These have greatly been threatened population growth and the construction of dams. The physical characteristics are similar to those of Indus river dolphin. The mature females are known to be larger than males with the females expressing sexual dimorphism after they reach about 150 cm long.
Amazon River Dolphin
Fourth on the list is the Amazon River dolphin, commonly known as the boto. It classified in the super family platanistoidea. It is also known to be the largest cetacean living in fresh water. It can even grow larger than a human with the body length ranging from 1.53 to 2.4 meters. The females are generally than males. The dolphins have unfused neck vertebrae which enables hem to turn their heads in an angle of 90 degrees. This flexibility is extremely important in navigation especially in the flooded forests.