The River Dolphins of South Asia

Posted on julio, 21 1999

The river dolphins of South Asia are blind, anti-social animals that spend most of their lives swimming on their sides. These dolphins never see the ocean, and are a far cry from the popular image of a friendly, leaping marine variety
Lahore, Pakistan: River dolphins are descended from marine dolphins and have adapted to life in fresh water, so they are no longer capable of surviving in the sea. This may be their undoing as the waterways in which they occur  the Indus, the Ganges and the Brahmaputra  run through some of the poorest and most densely populated regions on earth.

Millions of people use the rivers in any way they can, leaving little room for the dolphins and other freshwater creatures that rely on the rivers for their survival.

There are two closely related species of river dolphin in South Asia: the Indus dolphin, locally called the bhulan, and the Ganges dolphin or susu. Both are classified endangered by the International Union for the Conservation of Nature (IUCN) and are under threat from hunting, capture, water pollution, construction of dams and draining of rivers for irrigation.

These dolphins once occurred from the delta regions of the Indus and Ganges river systems up into the foothills of the Himalayas. Nowadays both these species are absent from much of their former upstream range and are recorded in fewer and fewer numbers in the lower regions. Even so, river dolphins are found in India, Pakistan and Bangladesh and in some areas of land-locked Nepal. Globally, there are four species of dolphin which live only in fresh water: the Indus and Ganges dolphins of South Asia, the critically endangered baiji or Yangtze river dolphin of China, and the Amazon river dolphin or boto in the Amazon and Orinoco river systems. The Yangtze dolphin has been the victim of rapid industrialization and fishing in China, and it is likely to become extinct in the near future. The Amazon dolphin is the only species which is neither endangered nor blind.

Very little was known of the South Asian river dolphins until 1969 when Georgio Pilleri, a Swiss scientist, captured dolphins in Pakistan and noticed their unique characteristics. When Pilleri observed the dolphins in the clear water of his laboratory, he noticed they were swimming on their sides almost all the time, becoming upright only when surfacing to breathe.

The South Asian dolphins often occur in water as shallow as 30 centimetres deep so they turn and swim on their sides. This side-swimming behaviour is not seen in any other species of cetacean.

Superficially, the South Asian river dolphins do not look like other dolphins. They have very wide flippers for stabilization in turbulent river waters, a small and stocky body, almost no dorsal fin and an extremely long beak. The blind Indus and the Ganges river dolphins have a tiny eye, no more than a pinhole, which can only detect the presence of light. This blindness is not a disability but an adaptation to living in turbid river environments.

Visibility in the Indus is only two to four centimetres as the sediment load of this tropical river is so high. The dolphins have developed a sonar system to "see" their environment, and they can navigate, locate prey, boats and other dolphins and differentiate between the size and species of fish with this echo-location system.

The tropical large river ecosystem in which the dolphins occur is not an isolated unit. The surrounding floodplains are an integral component of the system, which is characterized by annual flood cycles that leave fine nutrient-rich alluvial deposits on the fertile flood plain and return organic biomass to the water.

In the middle reaches, the rivers are many kilometres wide with biodiversity "hotspots" in large pools which are favourite feeding grounds for river dolphins and other South Asian aquatic animals. It is this variability in the river that provides a complex habitat and high biodiversity. Flood control schemes, embankments, dams and barrages inhibit the annual flood cycle and disrupt the natural river flow, reducing the natural variability and thereby biodiversity.

The most optimistic estimate for the Indus dolphin is about 500 individuals and pessimistic counts are as low as 250. Whatever the exact number, the Indus dolphin is unlikely to survive unless steps are taken to ensure its protection.

The Ganges dolphin has a wider distribution and is in less immediate danger of extinction, with current population estimates of about 5,000. However, both the Indus and the Ganges dolphin are at risk from pollution by pesticides and fertilizers and from agricultural practices on the floodplains. As South Asia develops, industrialization precedes environmental controls on emissions. Untreated effluents are released into rivers creating a highly toxic environment where little can survive.

The problem of bycatch of dolphins in fishing nets is hard to quantify as fishermen are generally reluctant to report kills. However, this is one of the major factors that influenced the demise of the baiji in China and is likely to be extremely influential in the survival of the South Asian dolphins. Poor education, high illiteracy rates and low environmental awareness among rural communities and fishermen are important factors in the decline of South Asian river dolphins.

The animals are viewed as something to be exploited and their oil is used to treat rheumatism and muscular pains. If we are even to begin to protect the river dolphins of South Asia, it is imperative to raise local people's awareness. They can either be the dolphins' protectors or just another factor in the ultimate disappearance of these unique animals.

(891 words)

*Gill Braulik is a marine biologist currently working with WWF-Pakistan