Alterations in Physico-chemical Parameters of Water and Aquatic Diversity at Maneri-Bhali Phase I Dam Site on River Ganges in District Uttarkashi, Uttarakhand - Management of Natural Resources in a Changing Environment - page 104

Table 4 Variation in number of fishes sampled before and after dam wall from river Ganges at
Maneri Bhali Phase I hydro-electric power project

Before dam wall After dam wall

Months No. of fishes No. of fishes

Aug. 20 8

Sept. 25 15

Oct. 44 25

Nov. 62 39

Dec. 44 17

Jan. 53 25

Feb. 86 35

March 93 38

April 60 32

May 45 24

June 25 18

July 16 8

Aug. 20 9

Sept. 25 12

Mean ± SEM 44.14 ± 6.15 21.7 ± 2.95

result in altered species characteristics. Also, legal mandates (e.g. the US National
Environmental Protection Act, 42 USC - 4321 to 4361 and the US Endangered Act,
16 USC - 1531 to 1544) require assessment of habitat and predication of changes to
it under different management scenarios. Such legislation spawn the development
of habitat models designed to quantify the effect of flow alterations and other habitat
changes on species populations (Terrell 1984 ; Orth 1987 ; Gore and Nestler 1988 ).
In specific case related to fishes, the blockage of fish movements upstream can
have a very significant and negative impact on fish biodiversity. Many findings
reveal that large number of aquatic fauna have been lost as a consequence. In the
Columbia River, USA, more than 200 stocks of anadromous, Pacific salmonids
became extinct. Sturgeon populations in the Caspian Sea rely on hatcheries, mainly
in Iran, since Russian dams block natural spawning migrations. Hydroelectric dams
in the Amazon basin have halted the long distance upstream migration of several
species of catfishes and interrupted the downstream migration of their larvae. On the
Araguaia-Tocantins River basin, Brazil, several species of migrating catfish have
been drastically reduced in abundance as a result of dams; catches in the down-
stream fisheries have been reduced by 70 %. Artificial barriers also lead to the
dramatic decline of the endangered cyprinid fish, Anaecypris hispanica in Iberia.
In general, a river is a one-way system for molluscs, as many molluscs can only
move downstream by drifting or being dislodged by flood events and moved down-
stream. But some species with a larval form can move significant distances upstream
with the aid of a third party, e.g. host fish during the larval stage. A single dam and
more significantly multiple dams along a given river interfere with the genetic
bridging function of the main stem.