Monday, July 30, 2007

River dolphin fact sheet

There are 3 species of river dolphins existing today, and four subspecies. River dolphins differ from oceanic dolphins not only because of their habitat but genetically as well. Because some oceanic dolphins can be found in brackish waters and fresh water (tucuxi, irrawaddy and humpback dolphins for example) and one of the river dolphins (Franciscana) also lives in coastal waters. They look very different physically, river dolphins have longer beaks (about 4 times as long), smaller eyes  and their eyesight is poorly developed as they live in dark water (sometimes blind and rely completely on echolocation) while many oceanic dolphins have good eyesight. 
The size vary from 1,5 to 2,4 m, males are larger then females. The colour can also vary from dark grey/black, grey and lighter grey, white, brown, pink. They feed on a variety of fish and they hunt together in smaller groups. They get sexually mature between 8 to 10 years old and are pregnant for 10 to 12 month, depending on the species. The young will drink milk for 1,5 to 2 years, but will start to eat fish at an age of 6 month.
The river dolphins are facing many threats and one species, the Yangtze river dolphin or baiji, went extinct in 2010, last sighted wild sighting was in 2004. A big threat is loss of habitat; dam building is trapping dolphins or keeping them out of their territory. This is also disturbing the habitat for their food, or destroying the migratory path for the prey. Unfortunately not even the river dolphins are safe from human greed of seeing them in captivity.  

Amazon river dolphin (Inia geoffrensis geoffrensis)
Orinoco river dolphin (Inia geoffrensis humboldtiana)
Bolivian river dolphin (Inia geoffrensis boliviensis)
Araguaian river dolphin (Inia geoffrensis araguaiaensis)

Ganges river dolphin (Platanista gangetica gangetica)
Indus river dolphin (Platanista gangetica minor)

Franciscana river dolphin (Pontoporia blainvillei)

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