display | more...

When I first heard about the Irrawaddy dolphin, I thought it was a joke. I was talking to a young Danish traveler about his adventures in Laos and what I should expect to see there when he mentioned them. He was telling me about the beauty, quiet and calm of the southern Mekong Islands when he said that on the ferry over to one of the islands he had seen dolphins.

"Yeah right!" I said, "Good one."

I was surprised at his quick imagination and thought that it was a good joke to try to pull over on someone. Not me, obviously, I was too quick for him. I mean, everyone knows that dolphins live in the ocean, not in rivers, don't they?

"I am not joking," he replied, looking rather offended at my laughter.

I looked at him more closely and realized he was telling the truth. There really were dolphins in the Mekong. I didn't get to see these creatures with my own eyes until almost a year later and despite hearing about them from other people, I still doubted their existence.

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Delphinidae
Genus: Orcaella
Species: Orcaella brevirostris

Range/Habitat

The Irrawaddy dolphins can be found in shallow coastal or freshwater systems in the tropical and south tropical Indo-Pacific Ocean. They are found in major river systems in south east Asia and India, specifically the Mekong. Irrawaddy dolphins were once common on the north coast of Australia, but like elsewhere, their numbers are dwindling.

Appearance

The Irrawaddy looks more like the finless porpoise than the dolphins you see at marina shows. The major difference of course being the presence of the dorsal fin. The Irrawaddy dolphin is gray in color and an average length between 2 and 2.75 meters. They weigh between 90-150 kg.

Both the tail and the neck are relatively flexible and it is written that facial expressions can be recognized. They have no beak and their blowholes are slightly off set to the left.

Irrawaddy dolphins are slow moving and generally not as playful as their open water cousins.

Reproduction

Little is known about the reproductive cycles of these dolphins because until recently they have not been well studied. Also, the mating season differs with location. Cambodian fishermen report that in the area around Kratie, mating season occurs from March to June.

The gestation period is about 14 months and calves are weaned after 2 years. They begin to eat fish at 6 months.

The average life span for the Irrawaddy dolphin is thought to be about 28-30 years.

Behaviour

Irrawaddy dolphins live in family groups of 6. They are not very active nor are they as playful as other dolphins. They don't perform the same leaps and jumps and they do not approach boats with curiosity. They have been reported to assist fisherman in Cambodia and Laos by herding fish into their nets.

Irrawaddy dolphins communicate in the same way as other dolphins: sonar signals.

Diet

Irrawaddy dolphins feed from the mid water level as well as from the bottom. They eat bony fish and crustaceans. Squid is sometimes a part of their diet.

Conservation Efforts

Dolphins are considered sacred in Cambodia and Vietnam and fishermen do no kill them for food. In Laos is it believed that dolphins are reincarnated humans and are protected against hunting by law. The dwindling supply of their staple diet fish is affecting population, however, and it is thought that there are less than 500 dolphins left in this river. Numbers in other parts of the Indo-Pacific region are unknown, but due to the rarer sightings, the Irrawaddy dolphin is thought to be the most in danger of extinction amongst the cetacea order. Due to the lack of accurate information and numbers, they are not currently on the endangered list.

Picture:
http://www.cetacea.org/irrawad.htm

Sources:
http://animaldiversity.ummz.umich.edu/accounts/orcaella/o._brevirostris$narrative.html#reproduction
http://abcnews.go.com/sections/science/DailyNews/dolphins990604.html
http://www.cetacea.org/irrawad.htm

Log in or register to write something here or to contact authors.