“One day, Plato defined humankind as the two-legged animal without feathers. The next day, they say, Diogenes dropped by at the Academy with a plucked chicken”.
Known to locals as the bhulan, the Indus susu is today mainly confined to a 100-mile stretch of fresh water between two artificial constructions, the Guddu and the Sukkur barrages, across the lower Indus in the province of Sindh, Pakistan. The bhulan, even more than its neighbour in the Ganga, is threatened with imminent extinction. As is the case with the earth’s other three river dolphin species, its fight for survival has not so much to do with adverse natural conditions as with problems manmade. Its diminishing numbers are a result of incidental and intentional exploitation by humans. A survey conducted jointly in 2001 by wwF-Pakistan, the Pakistan government wildlife departments and the Whale and Dolphin Conservation Society estimated that there are 1100 bhulans left in the Indus waters (see survey map). A total of 965 individuals were actually sighted.
Confined to the fresh-water river system of the Indus in Pakistan, the blind and side-swimming bhulan resembles the Indian susu in every respect, except that it is slightly smaller, as the specific name minor implies. Like other river dolphins, and unlike its ocean-going relatives, the bhulan has a bulbous forehead and a long rostrum, its skull has not undergone streamlining and the neck vertebrae are not fused, thereby allowing remarkable flexibility of the head, which may assist it in capturing prey, navigating in narrow waterways, and in scanning its surroundings. It too relies on echolocation to navigate and hunt. And, like the Ganga susu, the bhulan is a slow swimmer. Bhulans often swim on their right sides, nodding their heads continually, perhaps to maintain contact with the bottom of the river with their right flipper. Being quite blind, they appear to navigate through touch, the flipper serving much like a blind man’s stick.
Up until the 1970s, the Indus bhulan (Platanista minor) was not distinguished from the Ganga susu (Platanista gangetica) as a separate species. But, noting other distinctive features, G Pilleri and M Gihr in their paper ‘Zur Systematik der Gattung Platanista’, Cetacea, 1971, argued that since no size difference has been systematically documented, it is more appropriate to call the dolphin of the Indus, Platanista indi.
Other than by their range of geographic distribution, the two kinds of South Asian river dolphins are primarily differentiated on the basis of the anatomical details of their maxillary crests. These are flat, paired, oval extensions of the upper jaw-bone that grow upward and forward on the skull and occupy a horizontal position above and forward of the slit-like blowhole. As these differences are minor, some may still argue that the Indus and Ganga dolphins are the same species or are subspecies of a single species. Taxonomically, two groups of creatures are the same species if, in the wild, there is significant gene flow between the two gene pools (gene pool: the set of genetic information that defines a species).
Essentially, if two groups can inter-breed successfully they are the same species. Since the Indus and Ganga river dolphins are geographically isolated they are reproductively estranged. Still, if one adheres to Alan R Templeton’s definition of a species “as the most inclusive group of organisms having the potential for genetic and/or demographic exchangeability”, and in the case of the South Asian river dolphins there is such a situation, then is it not reasonable to club the Indus and Ganga river dolphins under one specific category, say Platanista southasiana?
Molecular biology night provide some answers. A molecular phylogenetic study (the study of the evolutionary history of a genetically related group of organisms) of river dolphins conducted by G Yang and K Zhou in 1999, published in Acta Theriologica Sinica, established that the difference between cytochrome-b (cyt-b) sequences of the Ganga and Indus river dolphins was very minor. Cyt-b is an ancient gene that occurs in the mitochondria of all nucleated organisms. As mitochondrial DNA is maternally inherited and evolves much faster than nuclear DNA, mitochondrial genes are the first place where genetic divergence is reflected. Therefore, Yang and Zhou’s observation that the cyt-b gene sequences of the Indus and Ganga river dolphins are not very different lends strong credence to the hypothesis that these two groups of riverine cetaceans have not diverged to an extent that justifies their being called different species.
Dams across the Indus and its tributaries restrict the movement of the bhulan, disrupt migration patterns and divide their population. Reliable data on the bhulan’s seasonal migratory behaviour still needs to be accumulated but there is some informed speculation on the subject. According to Richard Garstang, conservation advisor to WWF-Pakistan, “The Indus River barrages probably act as one-way valves, permitting inadvertent downstream movement but no return traffic”. The greatest threat to the survival of the bhulan, though, is probably from the continuing decline in water flow, especially downstream of the Sukkur barrage.
The construction of three irrigation barrages, completed at Sukkur in 1932, at Kotri in 1955, and at Guddu in 1969, greatly reduced the volume of water in the river, causing the dry-season range of movement of the dolphins to shrink. New diversion structures in the upper Indus, and overexploitation of the ground water that has resulted in increased demand for irrigation water from rivers have further reduced flow. Chemical pollutants from agricultural and urban waste, and noise pollution from boat traffic are suspected to- compound the problem of the degeneration of the bhulan habitat. Dolphin lives are also lost when they get entangled in fishing nets.
These threats to the survival of the bhulan are hardly typical to its case. River dolphins in the Ganga system too face the same hurdles to survival. Another argument then, for a common and concerted approach to the dolphins of the Subcontinent’s rivers, whether they be in Nepal, India or Pakistan?