River Dolphins In The Brahmaputra

One of the most frequently asked question during the beginning of my Brahmaputra River expeditions is “is that a grey or a pink river dolphin? And it is a valid question given that what visitor see from high on the observation deck are only glimpses of a distant dolphin surfacing to breath, before disappearing in the murky waters of the Brahmaputra. It is when we get to the glassy calm waters of the Brahmaputra River where both species of dolphin can be seen at close range from smaller fishing boats used for daily excursions. Nevertheless, while sightings from our smaller historic boats are made at closer range, and more detail can be gleaned, telling the pink from the gray river dolphin can be challenging unless one familiarizes with certain field marks.

To me, one of the most fulfilling experiences in the rainforest is being able to identify every bird and mammal by their looks and sounds. However, birds, mammals, insects and plants use specific habitats, have distinctive shapes, colors and sounds that one can use to identify by this unique characteristics or via the process of eliminations (e.g., large bird, dark in color, odd looking, found near water; that is likely to be a horned screamer). Rainforest animals are rather vocal as they use sounds to communicate in the dense rainforest foliage; their conversational sounds make identification easier. Moreover, rainforest animals can often be seen for extended periods allowing for study of characteristics leading to the species identification.

The challenge in identifying dolphins in the Brahmaputra River itself is that, of course, both species mingle together under water, they are often seen from a distance, and their coloration is not distinctive enough to allow a quick identification during the brief time the surface for air. Pink river dolphins can vary from pink to gray or pink/gray blotched in their dorsal or upper parts and generally pink in their underparts and belly. Gray river dolphins are light gray to blue-gray in color on their dorsal or upper parts, and light gray to pink on their ventral or under parts. Their flanks or sides are slightly lighter than their dorsal parts.

After seeing, photographing, and video-taping many dolphins at close range in the Brahmaputra River, I concluded that the shape of the their beaks provides a clue when the observer gets a good view. However, the most important field marks for a safe identification are the shape of their dorsal fin and back, and the sound dolphins produce when they surface for air.

Pink river dolphins are larger than their gray cousins are, but when they fish in mixed groups it is often difficult to tell them apart just by size. The gray river dolphin shows a triangular dorsal fin that is slightly hooked at their tips. The fin is well defined. The pink river dolphin shows a low, keel-shaped dorsal fin that extends from the mid-body to the base of the tail.

The sound dolphins make when the breath is very distinctive. The gray dolphins make a smooth yet clearly audible breathing sound as the blow air and spray water through their air hole. The pink dolphin makes a harsh sound that resembles a smoker’s cough. This distinctive sound allows for a quick identification even at nighttime. 

If you come to the Brahmaputra and see a dolphin, pay attention to the dorsal fin and the breathing sounds to quickly tell whether you are seeing a pink of gray river dolphin.