🐬 Irrawaddy Dolphin (Orcaella brevirostris) – The Gentle Guardian of Estuaries and Deltas

The Irrawaddy Dolphin (Orcaella brevirostris) is a rare and fascinating species of oceanic dolphin that thrives in coastal, estuarine, and freshwater ecosystems of South and Southeast Asia. Known for its shy nature and unique physical features, it is one of the most charismatic and ecologically significant mammals found in the Sundarbans mangrove delta.

Let’s explore its taxonomy, morphology, behavior, habitat, and conservation efforts, with a special focus on its presence in the Sundarbans.

📚 Taxonomy

• Kingdom: Animalia

• Phylum: Chordata

• Class: Mammalia

• Order: Cetacea

• Family: Delphinidae

• Genus: Orcaella

• Species: Orcaella brevirostris

• Common Name: Irrawaddy Dolphin

🐬 Morphology & Physical Description

• Size: Grows up to 2.3–2.7 meters in length

• Weight: Between 90–150 kg

• Color: Uniform slate grey to pale bluish-grey, lighter on the underside

• Head:

  • Rounded, bulging forehead with no distinct beak

  • Small, mobile triangular flippers

  • A short, barely visible dorsal fin

• Unique Trait: Lacks the characteristic “beak” seen in most dolphins, giving it a whale-like appearance

🌍 Habitat & Distribution

• Inhabits brackish and freshwater systems of Southeast Asia and the Bay of Bengal.

• Found in estuaries, mangrove creeks, rivers, and coastal shallows.

• Major populations are seen in the Irrawaddy River (Myanmar), Mekong River, Bangladesh, and India (Sundarbans and Chilika Lake).

🌟 Special Features & Behavior

🔹 Shy and Social

• Typically found in small groups of 2–6 individuals.

• Extremely shy and avoid boats, making them hard to spot.

🔹 Unique Communication

• Use a variety of clicks and whistles for echolocation and communication.

• Known to spit jets of water while herding fish – a rare behavior among dolphins.

🔹 Breathing and Diving

• Surfaces every 70–150 seconds to breathe

• Can dive for up to 12 minutes

🔹 Feeding Habits

• Diet includes fish, crustaceans, and cephalopods.

• Employs cooperative feeding and often herds fish towards the shore.

🌿 Presence in the Sundarbans

The Irrawaddy Dolphin is a flagship species of the Indian and Bangladeshi Sundarbans, where it inhabits the brackish water creeks and estuaries.

🐬 Role in the Sundarbans:

• Acts as an indicator species of healthy estuarine systems

• Its survival is closely tied to the balance of freshwater and salinity in the mangrove ecosystem

• Found mostly in rivers like the Raimangal, Matla, and Hooghly, where the mixing of salt and freshwater supports a rich diversity of fish

⚠️ Threats in the Sundarbans:

• Boat traffic and noise pollution, which disrupt their communication

• Entanglement in fishing gear and gillnets

• Pollution from upstream industrial discharge

• Salinity intrusion and climate change, altering the habitat balance

Conservation strategies include protected estuarine zones, fishing regulations, and promoting responsible wildlife tourism.

🚨 Conservation Status

• IUCN Red List: Endangered

• CITES Listing: Appendix I

• India’s Wildlife Protection Act, 1972: Schedule I

• Also protected under the CMS (Convention on Migratory Species) agreement

The Irrawaddy Dolphin is not only a captivating creature of estuarine waters but also a keystone species whose presence signifies a healthy river-mangrove ecosystem. Protecting its habitat in the Sundarbans is essential for preserving the biodiversity of this UNESCO World Heritage Site.

💡 Credit Note

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Discover more about this gentle dolphin species on Wikipedia – Irrawaddy Dolphin.