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Irrawaddy Dolphin (Orcaella brevirostris)

Irrawaddy Dolphin

Irrawaddy Dolphin

Author of the picture: C. Berjeau

Introduction

The Irrawaddy Dolphin is one that offers a distinctive appearance to it. They have a flexible neck which accounts for the creases at the back of the head. They are closely related to the Orca.

Description

This dolphin has a head that is round and they don’t have a beak at all. The forehead extends beyond the facial features. They are dark gray or dark blue in color and they have a lighter gray underneath. They feature a small dorsal fin and it is triangle in shaped with a round end. The Irrawaddy Dolphin has long and wide flippers. They can be from 70 inches to 108 inches long. They can weigh from 215 to 350 pounds.

The males tend to be longer and heavier than the females. They also have a dorsal fin that is bigger. The teeth of this dolphin are very narrow and pointy as well as peg light. They are located both in the lower and the upper jaw regions. This species of dolphin doesn’t have a cardiac sphincter. They also have a stomach with several divided compartments.

Distribution

The distribution areas of the Irrawaddy Dolphin are quite spread out. They have been found around the Philippines and into the Northeastern part of India. They are also found around the waters of the Indo-Pacific. The tend to stick to the shallow water areas around the coast. They are one of the few species of dolphins that can survive in freshwater locations.

Behavior

Diving is very frequent for this dolphin species. Every 70 to 150 seconds they have to come up for air. Often, it is only the head and perhaps the body that is seen when they surface for air. It is very seldom that you will see the Irrawaddy Dolphin with the tail out of the water. They aren’t seen as being as active as many of the other species.

They also tend to live in pods with smaller numbers than other dolphins. They are highly social but there may be from 3 to 6 members per pod. They are very curious about their surroundings and have been observed looking around when they surface for air to see what is around them.

Feeding

There are plenty of food items that this dolphin feeds upon. They include fish, crustaceans, and cephalopods. They have been seen spitting water, but it is still a mystery why they do so. One theory though is that this process helps them to round up schools of fish to feed upon. This is one species of dolphin that has been seen working with humans regarding cooperative fishing endeavors.

The fishermen get the attention of the Irrawaddy Dolphins by tapping on their boats with a wooden key. The dolphins will begin to swim in circles and in the center of those circles are the fish. The turbulence rounds them up and then the fishermen are able to properly set their nets to capture them. The dolphins consume the fish that get out and that are at the edges of the netting.

Reproduction

There isn’t very much information identified about mating for this species of dolphin. It is believed that they don’t breed within their small groups though and will interact with other pods for this purpose. Mating is believed to occur any time from December to June. The males are believed to be very competitive so that they can mate with as many females as possible.

The amount of time it takes for the calf to be born can range from 9 to 14 months. It depends on the location according to what has been observed by the experts. The females will usually have one offspring every 3 years. The young will stay with them closely for 2 years and then be fully weaned. The young will be introduced to fish and other foods though around 6 months of age. The average lifespan in the wild is 28 years.

Conservation Status and Threats

At this point in time, The Irrawaddy Dolphin is classified as a vulnerable species. There are about 6,000 of them in the wild and some conservation efforts in place to help protect them. Around Thailand there have been noted declined numbers and hat is a huge concern. The mortality rate is often blamed on commercial fishing entities and they are often encouraged to use safer equipment. Fishermen are also encouraged to watch out for dolphins in their nets so that they can be released.

The loss of habitat due to dams, mining, and other efforts also seem to be a problem for this dolphin and survival. It can be tough though to get those types of events stopped in order to protect them. In the areas of Cambodia, Vietnam, and Laos it is illegal to hunt the Irrawaddy Dolphin. However, enforcing such laws has proven to be very difficult.

sumber: http://www.dolphins-world.com/irrawaddy-dolphin/


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