Do you know the Odontocetes? Behind this clever name hides a whole family of cetaceans with toothed jaws. If you're familiar with majestic orcas and mysterious sperm whales, then you're already familiar with odontocetes. However, there is a subfamily that you may not know about: the Platanists. Platanists, these river dolphins, populate the waters of rivers, like their famous relative, the Yangtze dolphin in China. But Asia is also home to two other fascinating cousin specimens: the Indus dolphin and the Ganges dolphin (DG). The latter reigns supreme over the majestic waters of the Ganges and its tributaries, this immense river artery which, like a vein, crosses three nations: Nepal, India and Bangladesh.
Dolphin on the Karnali River
The story of this animal, first revealed in the writings of explorer William Roxburgh in 1801, took a captivating turn thanks to the research of French ethno-ketologist François-Xavier Pelletier in the late 1970s. His name may seem foreign at first glance, but you've probably already come across stories of his fascinating work on the complex bonds between man and animal. Pelletier, known for having revealed to the general public cetacean hunts in the Faroe Islands as well as the interactions between Imraguen fishermen and dolphins in Mauritania, has left his mark in the field. It was in 1977 that his attention turned to the Ganges dolphin, a moment that not only spawned the publication of the book “Ballad for a Sacred Dolphin” in 1988 about his “delphinasia” expedition, which was also immortalized on screen in a film made following numerous other research missions: “threatened dolphins” (TF1) –
Yet, despite these laudable efforts, the Ganges dolphin has been relegated to obscurity, both on the Western and Asian sides. Although it has become the aquatic emblem of India, its presence remains largely unknown. This is the first dilemma surrounding this almost mystical being: if no one becomes aware of its existence, it is unlikely that measures will be taken to ensure its preservation.
Rostrum of the Ganges dolphin
The Ganges dolphin is distinguished by its unique morphology. Its rostrum, decorated with numerous teeth (116 pointed and conical teeth), is strangely reminiscent of the mouth of the crocodile Gavial, an inhabitant of the same waters. His environment, the turbid waters of the Ganges, has shaped his vision, which is reduced due to this opacity. (eye devoid of lens and pigmented epithelium, very reduced optic nerve (distinguishes only light and darkness). Very useful when it comes to the surface. However, its exceptionally developed melon allows it to navigate with ease thanks to echolocation, like a natural sonar, essential for survival in the waters of the Ganges (frequency from 1 to 300 kHz)
The task of accurately determining the current population of Ganges dolphins, whether in the rushing waters of the Ganges itself or in its tributary streams, is proving daunting. Dolphins, quick to surface and breathe, blend into the murky waters, complicating their census. These waterways extend over considerable areas, further exacerbating the complexity of the task. However, current estimates put the remaining population between Nepal and the marine estuaries of Bangladesh at around 2500 individuals.
In the past, François-Xavier Pelletier witnessed the hunting of dolphins, a practice which targeted their fat, once prized for its medicinal virtues and its aphrodisiac sex, according to traditional beliefs. Although this hunting has almost completely disappeared today, it has left a deep imprint. Nepal and India have banned the practice, making it punishable by law. Nowadays, it is easier to recover dolphin remains accidentally caught in nets, a by-product of fishing. On the other hand, the fall in dolphin populations has probably prevented fishing for industrial purposes aimed at exploiting the virtues of products derived from dolphins.
Banned gill nets laid on the banks of the Koshi River
Fishing and nets represent a real scourge for dolphins. Gill nets, popular with fishermen, often turn into fatal traps for dolphins. These creatures sometimes approach these nets to retrieve prey, become entangled, get injured, or even die. The consequences are sometimes tragic: a broken rostrum hinders their ability to feed properly, leading them inexorably to their doom. If this conflict highlights a struggle between fishermen and dolphins, gillnets have been banned in Nepal. However, the application of these restrictions remains pending, in a country where the priorities for residents are multiple and complex.
The rivers, for their part, are home to nearly 240 species of fish and reptiles. Over the centuries, man, increasingly equipped, has intensified his fishing, thus entering into direct competition with dolphins. Nowadays, catches are smaller and less frequent, reflecting the pressure on aquatic ecosystems. Certain destructive fishing methods were experimented with but quickly abandoned, such as electric fishing which destroys everything in its path without distinction.
Koshi Tapu Electric Dam
In the 21st century, all powers are seeking by all means to develop energy sources. India has taken up this challenge by creating numerous electric dams along the Ganges, but also in its tributaries and even in its neighboring countries. One of the first dams built in India, at Farakka in 1972, was just the beginning of a long list of infrastructure that has since been blamed for declining dolphin populations. In Nepal, this is the case for the Karnali, Narani and Koshi rivers. These dams have isolated some dolphin populations, preventing them from migrating upstream or downstream. As a result, dolphin populations are fragmented, making their survival increasingly precarious.
However, solutions are within reach: the creation of special waterways, allowing dolphins to migrate freely, could be a viable alternative, provided that India, Nepal and Bangladesh agree on their implementation . Translocation, that is to say the movement of individuals between groups, could also help to revitalize the fragile genetic heritage of these creatures.
Some scientists argue that the presence of dolphins is an indicator of water quality, but it is important to recognize that this statement represents a simplistic shortcut and a somewhat idealized perspective of reality. The Platanist easily frequents very polluted waters, such as the highly industrialized Hoogly River.
River pollution in Koshi
In reality, the situation of Ganges dolphins is much more complex and darker. Currently, these dolphins find themselves confined in the meanders of a fragmented river, considerably limiting their possibilities of movement and migration. They struggle for survival amid general indifference and ignorance.
If concrete and decisive measures are not taken quickly, there are fears that these dolphins will share the sad fate of their Yangtze cousins, now considered extinct forever.
sources:
Francois-Xavier Pelletier: http://www.hommenature.com/
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