Earlier this week, the Ministry of Environment, Forests and Climate Change launched the findings of a inhabitants research of dolphins present in Indian rivers, placing their numbers at 6,327. These playful creatures with their torpedo-like our bodies generate pleasure every time they’re noticed. People flock to see them. Urban youngsters describe them as ‘cute’.
There are two sorts of river dolphins. Facultative river dolphins happen in each marine and contemporary waters. In India, Irrawaddy dolphins are seen across the Chilka lake, the place an estimated 155 of those are a serious vacationer attraction, and off the Sunderbans. The smaller tucuxi is discovered within the Amazon and Orinoco rivers, and the Yangtze finless porpoise is about 1 metre lengthy.
Obligate river dolphins are discovered solely in contemporary water our bodies. The Yangtze river dolphin of China is presumed to be extinct, having been final noticed in 2007. The distinctively pink Amazon river dolphin is over 2.5 metres lengthy. The equally massive Ganges river dolphin has a widespread habitat, and is present in the primary our bodies and a few tributaries of the Ganges and the Brahmaputra.
Closely associated to the Ganges dolphin, the Indus river dolphin is the State aquatic animal of Punjab. Here, it’s discovered within the river Beas and its Harike wetlands within the Tarn Taran district. The Environment Ministry research may find solely three of those dolphins, indicating their precarious existence. Only about 1,800 survive within the Indus in Pakistan.
Adapting to muddy water
Dolphins and toothed whales have a outstanding, fatty mass on their foreheads known as the melon. It acts as a lens that focuses sound, and is essential in echolocation. Our river dolphins desire waters which are muddy, with low salt content material. An uncommon function of the Ganges and Indus river dolphins is their poor eyesight. Navigation and feeding is completed by echolocation, the place ultrasound waves, within the type of distinctive clicks, are emanated from their vocal chords, and the melon on the brow is used to sense the echoes of those waves bouncing off close by objects. These dolphins additionally present an inclination to swim on their sides, utilizing the fins on the perimeters of our bodies to really feel alongside the underside of riverbeds of their seek for meals.
In our river dolphin species, the attention is barely a centimeter throughout, and has a thick cornea and no eye lens. The retina has only a few cells for registering mild, and the optic nerve that carries visible sensations to the mind is skinny, barely a filament. Visual notion appears restricted to detecting mild, and the route from which mild is coming. Comparisons of mind areas concerned in sensory notion in these river dolphins with the marine bottlenose dolphin reveals that the sight areas are unusually small, and the listening to areas a lot bigger. This signifies a reliance on their biosonar for echolocation. In experiments, Indus river dolphins can detect a 4 mm ball bearing suspended on a nylon thread, and rapidly head for it.
Human hazard to river dolphins comes from the usage of their oil in cures for situations starting from muscular strains to arthritis. Overfishing deprives their meals provide, and they’re snared in fishing nets as undesirable bycatch. Chemical pollution pose one other hazard.
Despite more and more refined counting strategies, river dolphin inhabitants tendencies stay unclear – they could possibly be rising or falling. Either method, their numbers are critically low. We should foster higher public consciousness of those outstanding creatures.
(The article was written in collaboration with Sushil Chandani, who works in molecular modelling. sushilchandani@gmail.com)
Published – March 08, 2025 09:14 pm IST
