Guwahati: Construction of large dams on the Brahmaputra and its tributaries, being opposed by many quarters, is also posing a serious threat to river Dolphins which are on the verge of extinction.
Noted dolphin expert Dr Abdul Wakid said the Brahmaputra river system in Assam is considered as one of the last refuges of the species unimpeded by dams in its sea-bound flow compared to the Ganga.
"But the situation will change once the dams come up on the river`s tributaries and forerunners as proposed in Arunachal Pradesh and Meghalaya," Wakid, also the head of Aaranyak`s Gangetic Dolphin Research and Conservation
In a recent survey conducted in the entire Brahmaputra river system, a team, led by Wakid, recorded the existence of 264 dolphins. Of them, 212 dolphins are in the Brahmaputra mainstream, 29 dolphins in Kulsi river and 23 in Subansiri river.
Among the 168 dams proposed to be built in the Northeast, the Lower Siang, Dibang, Lower Demwe, Lower Subansiri and Kulsi dams have been identified as the most hreatening dams for the survival of Brahmaputra dolphins, Wakid pointed out.
Construction of dams causes major changes in flow regime, sediment load and water quality of running water besides degrading the dynamic attributes of downstream water and reduce the flow of sediments essential to the formation of stream channel islands and bars, Wakid said.
"Dams suppress natural fluctuations in flow and temperature which encompass optimum conditions for large number of aquatic organisms and the number of ecological niches for supporting diverse biotic communities is reduced," Wakid said.
The combination of these radical changes in environment and ecology downstream of the dams in all likelihood will affect the river dolphins by changing the type and seasonal availability of prey, changing the geomorphology of dolphin habitat and disrupting the natural flow regime of the river, he said.
The Siang, Dibang and Lohit rivers are the main water sources for Brahmaputra and its water flow level will fluctuate greatly when the proposed dams begin operation.
"These huge flow fluctuations will result in rapid unpredictable increases and decreases in depth and velocity.
This will cause a reduction in fish diversity and abundance which in turn will affect the prey-base of dolphins and also the Brahmaputra riverine ecosystem," he pointed out.
Construction of the proposed dams may reduce the upstream distribution of dolphins in the concerned rivers and block any upstream migration.
The most relevant example is the Ranganadi river of Assam`s Lakhimpur district which reduces the summer distribution of river dolphins in this river by about 30 KMs, Wakid said.