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Protection of an endangered fish Tor tor and Tor putitora population impacted by transportation network in the area of Tehri Dam Project, Garhwal Himalaya, India


Sound ecological practices in development of roads and highways are essential to protect the fragile ecosystem of the Himalayan mountains in northern India. Evidence is growing that the expanding, poorly designed network of roads and trails is a major cause of habitat fragmentation and degradation of both terrestrial and aquatic habitats. These effects have been quantified for two similar species of fish, collectively known as the Mahseer, which comprises Tor tor Hamilton and Tor putitora Hamilton, in the area of the construction of the Tehri Dam Project, located in the Garhwal Himalaya, India. The Tehri Dam Project will be one of Asia’s highest dams (260.5 meters height), and fifth highest in the world. It is being constructed approximately 1.5 kilometers downstream of the confluence of the Bhagirathi and Bhilangana, which together form the Ganges River after meeting the Alaknanda River (30 degrees, 23 minutes N; 78 degrees 29 minutes E). The dam is a multipurpose project which costs more than 8,000 crores of Indian rupees (USD: $1,780 million). It will generate 2,400 M.W. of electricity, and irrigate 2.7 million hectares (6.6 million acres) of land, plus provide municipal drinking water to a large population. New roads have been constructed along the banks and in the riparian zone of the two rivers. This has introduced large amounts of woody debris and sediments into the waterways, resulting in drastic changes in the physico-chemical and biological profile of the aquatic ecosystem. Detrimental effects on transparency, current velocity, conductivity, substrate composition, dissolved oxygen and benthic communities have been documented. Feeding, spawning and migration routes of Mahseer have been degraded or destroyed. Subsequent to road development, standing crop estimates of Mahseer declined from a maximum mean monthly biomass of 0.492 g.m-2 (February) to 0.185 g.m-2, a 62% decrease, and a minimum monthly mean biomass (July-August) of 0.185 g.m-2 to 0.014 g.m-2, a 92% decrease. Annual productivity of Mahseer declined from 0.198 g.m-2.yr-1 to 0.054 g.m-2.yr-1 (73 percent). This decline is believed to have been caused by increase in turbidity, accompanied by a decline in dissolve oxygen, decrease in general benthic productivity, and loss of cover. We have recommended the following measures to restore habitat quality and connectivity for the Mahseer: stream restoration and stream bank stabilization, gravel mining and dredging in the impacted sites, protecting of riparian vegetation, monitoring of water quality, enhancement of fish food reserves, rehabilitation of Mahseer in a hatchery / nursery, ecofriendly techniques for road development and maintenance, and the establishment of strong working partnerships among civil engineers, environmental biologists and the public.

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