What kind of animal is the River Dolphin? We will explain its characteristics, ecology, and habitat. It is a Southeast Asian dolphin, and some can be seen in northern Australia, so its habitat is very wide, but it is actually designated as an endangered species. Let’s take a closer look at the details.
What is a River Dolphin? Basic Stats
The Irrawaddy Dolphin is a marine mammal that belongs to the genus Orcaella, family Delphinidae, suborder Odontoceti, order Cetacea. Its English name is 河巨頭, and its scientific name is Orcaella brevirostris. The list of information is as follows. Its total length is over 2m and its weight exceeds 100kg.
| Japanese（和名） | カワゴンドウ |
| English（英名） | Irrawaddy Dolphin |
| scientific name(学名) | Orcaella brevirostris |
| classification（分類） | Mammalia、Odontoceti、 Delphinidae、Orcaella 哺乳綱、ハクジラ亜目、マイルカ科、カワゴンドウ属 |
| IUCN Status(保全状況) | ENDANGERED |
| Length（体長） | 2m |
| Weight（体重） | 130kg |
Classification
River whales were recognized in 1866 when they were reported as a new species by Richard Owen. Genetically, they are closer to killer whales than to dolphins. The Australian river whale is found in Australia and is becoming recognized as a separate species.
Taxonomy of River Dolphins
- 界（Kingdom）: 動物界 (Animalia)
- 門（Phylum）: 脊索動物門 (Chordata)
- 綱（Class）: 哺乳綱 (Mammalia)
- 目（Order）: 鯨偶蹄目 / 鯨目 (Cetacea)
- 亜目（Suborder）: 歯鯨亜目 (Odontoceti)
- 科（Family）: ハクジラ科 (Delphinidae)
- 属（Genus）: ゴンドウクジラ属 (Orcaella)
- 種（Species）:
- カワゴンドウ（淡水系個体群）: Orcaella brevirostris
- 近縁種: 海洋性のゴンドウクジラ (Orcaella brevirostris) とは同種だが、生息域が川や沿岸域に限定される。
Habitat
They are found in Southeast Asia (India, Bangladesh, Myanmar, Thailand, Indonesia, Cambodia, Philippines) and northern Australia. River whales can also be found in the Mekong River and Ayeyarwady River.
Main Habitats
Rivers of Asia
Mekong River (Laos, Cambodia, Thailand, Vietnam)
The world’s best-known freshwater population. It is listed as endangered, with an estimated population of only a few hundred individuals.
Indus River (Pakistan)
Small populations exist, but their numbers are extremely small.
Rivers of India
Lower Ganges River Basin
Although reported at one time, their population may have declined dramatically in recent years.
Coastal and brackish waters of Southeast Asia
Estuarine estuaries and lagoons in Malaysia and Indonesia
Populations adapted to brackish waters where freshwater and seawater mix.
China
Yangtze River
There once existed a population known as the “Yangtze River dolphin,” but the remaining individuals are considered nearly extinct.
Habitat Characteristics
Freshwater: Mid- to lower reaches of rivers, with relatively slow currents.
Brackish water: Places where seawater and freshwater mix, such as river estuaries and lagoons.
Depth: They feed on fish in relatively shallow rivers where the bottom is visible.
Impact of human activities: Their habitat is shrinking due to dam construction, shipping traffic, and water pollution.
What are its characteristics? What is it like?
The river whale has no beak and looks similar to a finless porpoise or a beluga whale. Its entire body is brown with a lighter color underside. Its lips are flexible and it can blow water out of its mouth. It inhabits the warm coastal waters and rivers from the Bay of Bengal to northern Australia. It swims by rotating as it rises and only raises its tail above the water when it dives.
- Physical Characteristics
Size
Adults measure approximately 2-2.5 m in length and weigh around 90-150 kg.
Body Shape
Their dorsal fin is small and round (not nearly triangular, but turtle-shell shaped).
They have a rounded head, a dolphin-like face, and a short snout.
Their body color is gray to pale blue-gray, with a whitish underside.
Unique Features
Because they belong to the Pilot Whale genus, they have a rounder shape than typical dolphins.
They are similar to oceanic pilot whales, but the freshwater species is slightly smaller and slender.
- Behavior and Ecology
Primaries
They often live in small groups (5-20 individuals).
Diet
They feed on fish and small crustaceans.
They are adept at catching fish even in shallow rivers.
Swimming
They live in rivers with a leisurely pace, rather than fast swimming.
Calls
They communicate with high-pitched clicks and calls.
Reproduction
Mothers care for their young for long periods of time.
They give birth to one calf at a time.
- Ecological Characteristics
Because they are adapted to freshwater and brackish waters, their body shape is suited to river currents, something not seen in marine dolphins.
Their dorsal fins are small, allowing them to swim in shallow waters, reducing resistance from currents.
Because they live in rivers close to human habitation, they are heavily affected by boats and fishing.
What is its personality like?
The river whale, like other dolphins, has a very gentle and calm personality.
River Whales’ Personality and Behavior
Gentle and calm
They often swim leisurely in rivers and rarely become suddenly aggressive.
They are relatively docile toward humans and may approach them out of curiosity (however, contact with wild individuals is dangerous).
Highly curious
They may approach boats or anglers and are sensitive to changes in their surroundings.
They may also play with floating objects or bubbles on the water’s surface.
Social
They live in small family or parent-child groups.
They actively communicate with each other (by calling and clicking).
They exhibit cooperative behavior within the group to protect and care for their young.
They can also be timid.
They are sensitive to strong currents, boat noise, and large-scale fishing activity.
They will suddenly flee as a group if they sense danger.
Playful
They have been observed jumping on the water surface and splashing with their tails and bodies.
In river environments, they also play games with fish in shallow waters, chasing each other.
What is its ecology like?
The river whale mainly eats squid and fish. It lives by eating creatures that live on the bottom of the water. Its lifespan is about 30 years.
- Habitat
Freshwater rivers: Live in shallow areas and winding channels in the mid- to lower reaches.
Brackish waters: Live in places where freshwater and saltwater mix, such as estuaries and lagoons.
Water depth: Can catch fish in shallow rivers.
Impacts of human activity: Boat traffic, fishing, water pollution, and dam construction limit their habitat.
- Diet (What do they eat?)
Mainly fish (carp, catfish, freshwater fish, etc.)
Also prey on small crustaceans.
Preying method
Work together in schools to drive and catch fish.
Because rivers are shallow, they hunt by jumping and circling.
- Behavior
School Life: Usually small groups of 5-20 individuals.
Swimming Pattern: Often swims slowly in rivers, rarely making sudden movements.
Calls/Communication:
Communicates with peers using high-frequency clicks and whistling calls.
May alter sounds to suit the river environment.
- Reproduction
Gestation Period: Approximately 10-12 months.
Birth: One baby at a time.
Rearing: Mothers take the lead in caring for the baby for an extended period.
Sexual Maturity: Females reach sexual maturity at approximately 5-10 years, males slightly later.
- Adaptations and Characteristics
Small dorsal fin → Easier to swim in shallow, flowing rivers.
Small, rounded body → Adapted to river navigation and prey hunting.
Timid and cautious → Sensitive to boats and humans.
Do they have any natural enemies?
Sharks are the biggest threat to the river whale.
About Baby River Whales
Baby River Whales (juveniles) have the following characteristics. Because they are adapted to life in rivers and estuaries, they exhibit behaviors and ecology slightly different from adults.
- Physical Characteristics
Body Length: Approximately 80-100 cm at birth
Weight: Approximately 10-15 kg
Body Color: Light gray, slightly darker on the back, and whitish on the ventral side
Dorsal Fin: Small, rounded, the same shape as adults
- Behavior and Personality
Dependent on Mother: For about a year after birth, they swim close to their mother, protecting them from food and danger.
Playful: They jump on the water surface and chase each other with their mother and siblings.
Learning Behavior:
They learn how to hunt and catch fish from their mother.
They also practice adjusting to the currents of rivers.
Sociability: They learn to communicate with their group members early on.
- Biological Features
Diet: Breastfed for the first few months of life.
Weaning: Around 6-12 months of age, babies gradually begin eating fish.
Growth: Over the course of 1-2 years, they nearly double their body length and become capable of moving like an adult.
Dangers: Young babies are at high risk of accidents in shallow rivers, due to boat traffic, and becoming entangled in fishing gear.
Are River Dolphins Endangered?
River dolphins are designated as an endangered species. Their population is declining due to humans, with the biggest threat being capture for the purpose of catching oil. Decreasing population and shrinking habitat are major issues, and habitat fragmentation has also occurred. In the early 2000s, the number of individuals dropped dramatically to just around 50, and complete extinction was feared. However, conservation efforts are progressing, and the population is beginning to increase.
- International Union for Conservation of Nature (IUCN) Assessment
Freshwater river populations (e.g., Mekong River, Yangtze River)
Some populations are classified as “Endangered” (EN) or “Critically Endangered” (CR) on the IUCN Red List.
For example, the Mekong River river dolphin is Endangered (EN).
The Yangtze River river dolphin is considered nearly extinct.
Marine populations
Coastal-dwelling pilot whales are sometimes classified as Vulnerable (VU).
- Reasons for Endangerment
Habitat Destruction
Dam Construction and Channel Improvements Divide River Environments
Changes in Flow Speed and Depth, Reducing Feeding Grounds
Conflicts with Fisheries
Frequent Entanglement in Nets and Fishing Gear
Dwindling Fish Stocks Lead to Less Food
Water Pollution
Deteriorating River Water Quality Due to Industrial Wastewater and Pesticides
Vessel Traffic
Collisions Caused by Vessel Traffic on Rivers
Low Reproductive Rate
Small Herds and Low Number of Offspring
Can River Dolphins be kept as pets?
River dolphins are an endangered species and cannot be kept by the general public. We recommend viewing them at an aquarium or other venue and being guided through events. You can see them at dolphin shows.
- Legal and Conservation Issues
Designated as an endangered species, capture and sale are strictly regulated internationally (listed under CITES Appendix I or II).
Capturing and keeping wild river dolphins is illegal in Japan.
Overseas, captivity is generally permitted only in special research facilities and aquariums.
- Ecologically Difficult to Keep
Requires a vast freshwater or brackish water environment.
Recreating the flow of a river or estuary is nearly impossible.
Special dietary habits.
Eat large amounts of raw fish and must learn predatory behavior.
Highly social.
Living in small groups, keeping them alone is stressful.
Health management is difficult.
Wild individuals are sensitive to disease and stress, and there are few examples of them surviving long lives in artificial environments.
- Aquarium Breeding
Marine pilot whales and freshwater river dolphins are only kept in limited numbers in specialized facilities.
They are extremely rare in Japanese aquariums and are rarely observed.
Breeding them requires large pools, specialized staff, and the constant presence of veterinarians.
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