Chapter 6

IMPACT OF TEHRI DAM ON COLDWATER FISH RESOURCES

The dams are constructed for the welfare of human beings for irrigation, flood control,

navigation and hydroelectric power generation. The generation of power has become

necessary for meeting the increasing demand of the country. The newly carved out state

Uttarakhand has the vast potential for tapping water resources for hydroelectric

generation. The Government of Uttarakhand has planned its development through Urja

Pradesh (Power State). However, the dams have deleterious effects on the fish

resources and their aquatic habitats. Dams interrupt stream flow and generate

hydrological changes along the integrated continuum of river ecosystems (Vanote et al.,

1980; Junk et al., 1989) that ultimately can be reflected in their associated fisheries. The

most obvious effects from constructing dams on rivers result from formation of new

lentic or semi-lentic environments upstream from the dam, and tailwater environments

downstream from the dam in addition to several adverse impacts on river morphology,

physico-chemical degradation of lotic environment and depression in aquatic biotic

components during the dam construction phase. Degradation of the aquatic environment

ultimately affects the fish communities in many ways. The fish, as all other

poikilotherms, is highly susceptible to changes in ecological conditions of their habitats.

Fish production is directly influenced by fish growth, which in turn is dependent largely

on food availability, feeding rate and the nutritional value of the food ingested

(Welcomme, 2001).

One of the most obvious and immediate effects when a dam is constructed is the

prevention of the longitudinal migration of fishes. The dams also affect the fish

community structures by altering their habitat as well as their feeding and spawning

grounds downstream (Beamesderfer et al., 1995; Geist et al., 1996; Zhong and Power,

1996; Horwath et al., 1998; Thomaz et al., 1999; Asianics Agro-Dev, 2000; Ferreira et

al., 2001; Mishra et al., 2002; Kouamelan et al., 2003; Camargo et al., 2004; Oliveira et

al., 2004; Potts and Khumalo, 2005). River and lake engineering have been responsible

for the immediate elimination of fish species in many freshwater systems all over the

world. Migratory species are particularly threatened by dams and other obstructions on

water courses if they are unable to reach their spawning grounds, may become extinct

ultimately. Engineering works also completely destroy the habitat of fish, often by

dredging or siltation of the river or lake bed. Along the stream continuum, dams and

their upstream reservoirs have downstream effects on riverine environments and

subsequently, diverse influences on downstream fishes, even beyond the lotic

ecosystem. Cumulative effects of dams in catchment basins and tributary stream can

significantly block nutrient flow throughout the ecosystem, affecting fish production

(Welcomme, 1985). Several environmental issues related to dams and fish migration

have been discussed during the Final Draft of ‘World Commission on Dams’, on June

30, 2000. A total of 126 papers on the impacts of dam construction on fish resources of

different countries were considered for making the final recommendations.

The measurement of fish production is potentially a useful tool to fishery

management in rivers and reservoirs. Not only it can be used to assess the impact of

environmental change on the well-being of a population, but it can lead to an estimate

of the optimum harvest (or yield) for a particular fishery (Mann and Penczak, 1986).

Following the inaugural studies by Ricker and Forester (1948) and Allen (1951) on

Oncorhynchus nerka and Salmo trutta, respectively, the annual production of any fish

species has been estimated for a variety of waters. The International Biological

Programme (1964-1974) provided a useful stimulus to production studies at all trophic

levels and led, directly or indirectly, several review articles pertaining on fish

(Chapman, 1978; Waters, 1977; Morgan et al., 1980; Neves, 1981 and Mann and

Penczak, 1986). Fish production (Ivlev, 1945) as a major pathway of energy flow

(Waters, 1977) at population and assemblage levels has been intensively studied in

Holarctic streams (Mann and Penczak, 1986) and lakes (Randall et al., 1995) but only a

few scattered reports deal with the production rates of stream fish from other

zoogeographical regions are available (Hopkins, 1971; Bishop, 1973; Watson and

Balon, 1984; Penczak and Lasso, 1991 and Agostinho and Penczak, 1995). Within the

Neotropics, the relatively considerable literature on large river fish populations such as

on the Rivers Amazon, Madeira and Parana is available (Goulding, 1981; Goulding et

al., 1988; Junk et al., 1989; Agostinho and Zalewski, 1996 and Mazzoni and Lobo´n-

Cervia, 2000). In America and Asia, numerous studies focused on the effects of

environmental alteration on fish communities and other aquatic organisms (Mathews et

al., 1988; Resh et al., 1988; Fausch and Bramblett, 1991; Robert, 1995; Kvernevik,

1997; Sugunan, 1997; Martin-Smith, 1998; Brown, 2000; Sugunan, 2000; Ferreira et

al., 2001). In tropical Africa, also few studies examined the effect of environmental

degradation on the biodiversity of aquatic organisms (Ogutu-Ohwayo, 1993; Ogutu-

Ohwayo et al., 1997; Kamden and Teugels, 1998; Sugunan, 2000; Kouamelan et al.,

2003). Few studies have also been made on the impacts of dams and impoundments on

fisheries in China (Zhou et al., 1980; Yu et al., 1981; Li, 1987; Yuan and Huang, 1989;

Chen et al., 1990; Lieu et al., 1994 and Zhong and Power, 1996).

An examination of world’s literature on fish production studies reveal a

domination of the work in Europe (England, Scotland, Wales, Denmark, Bulgaria,

Spain, Poland, Norway, Czechoslovakia), North America, Canada and U.S.A. Few data

are also found for rivers outside these countries. Allen (1951) and Hopkins (1971)

reported work on the streams in New Zealand; Bishop (1973) on small Malayan River

and Watson and Balon (1984) on rain forest stream of Northern Borneo. Very few

papers are available regarding the effect of anthropogenic perturbations on fish

production. Some of the contributions have been made on fish production and fisheries

in general, as influenced by habitat modifications (Alabaster, 1985), highway

construction (Barton, 1977), channelisation (Duvel et al., 1976; McCarthy, 1985),

navigation (Nielsen et al., 1986) traffic (Donald et al., 1986), agriculture activities

(Hesthagen et al., 1986), gravel extraction (Power, 1973), suspended solids of industrial

origin (Herbert et al., 1961; Alabaster, 1972; Alabaster and Lloyd, 1980 and Scullion

and Edwards, 1980), other human impacts (Penczak and Mann, 1987) and

impoundments (Penczak et al., 1984; Backiel, 1985; Crisp, 1985; Porcher and Travade,

1992; Ogutu-Ohwayo, 1993; Travnichek and Maceina, 1994; Zhong and Power, 1996;

Ogutu-Ohwayo et al., 1997; Horwath et al., 1998; Kamden and Teugels, 1998; Ponton

and Vauchel, 1998; Cazaubon and Giudicelli, 1999; Thomaz et al., 1999; Brown, 2000;

Sugunan, 2000; Jha et al., 2001; Marmulla, 2001; Rolauffs et al., 2001; Mishra et al.,

2002; Kouamelan et al., 2003; Jakob et al., 2003; Camargo et al., 2004; Oliveira et al.,

2004; Chakrabarty and Das, 2005; Potts and Khumalo, 2005; Thomson et al., 2005;

Brummett, 2006; Welcomme, 2006).

Unfortunately, as far as the contribution on fish production studies in India is

concerned, it is almost negligible. Sreenivasan (1972) and Ganpati and Srinivasan

(1972) have done work on some aspects of fish production and energy flow in some

South Indian ponds and swamps. Also few studies on fish population have also been

made on the reservoirs of Punjab, Nangal Dam, Talwara Dam and Pong Dam by Gill

(1984), on the dams made on Hoogly, Godavari, Krishna and Cauvery Rivers by

Sandhu and Toor (1984) and in Ganges by Sugunan (1995). But no detailed work has

been done so far on fish production of any natural or stressed environment of the

country. This problem of paucity of information related to fish production studies in the

Asian countries has been highlighted from time to time in several IBP publications and

it was attributed to the absence of trained workers or specialists in the discipline of

‘Production Ecology of Fish’. As far as the aspect of dams and fish is concerned, some

work has already been reported in India on the deleterious effects of impoundments on

fish life, especially the migration of the fish (Hora and Nair, 1940; Raj, 1941; Chacko,

1952; Pantalu et al., 1966; Rao and Palta, 1973; Sehgal, 1989; Sugunan, 1995;

Sugunan, 2000; Jackson and Marmulla, 2001 and Mishra et al., 2002). The studies

made by all of them were generally made after the completion of dams; but no sincere

attempt has been made on the ecological effects of dams on fish resources during the

construction phase of dams. A significant work has been done on the impact of Tehri

Dam on the dynamics of biological production of Bhagirathi during 1983-87 (Sharma,

1991). However, no work has been done after this to manifest the impact on fish

resources, which are the most affected element of life due to Tehri Dam construction.

Therefore, it was felt necessary to fill up the gap on human knowledge on this very

important aspect of Environmental Biology of Fish. The importance of the work for

undertaking it on priority basis was felt, as the Tehri Dam is on the verge of

completion. The present study was focused on the impact of Tehri Dam construction on

fish habitats, feeding, breeding and spawning grounds in general and impact on

production of the Snow trout (Schizothorax richardsonii Gray; S. sinuatus Heckel and

Schizothoraichthys progastus McClelland) and Mahseer (Tor tor Hamilton and Tor

putitora Hamilton) in particular. Therefore, an attempt has been made on the diversity,

fish catch composition, fish biology (feeding, spawning, migration), production of fish

species (snow-trout and mahseer) and downstream/tailrace fish resources of the

Bhagirathi River influenced by Tehri Dam construction. The present study on the

impact of Tehri Dam on the coldwater fish resources was undertaken during the

construction phase and after impoundment, so that the ameliorative measures can be

recommended for minimizing the negative impact with the suggestions for the

management and sustainable development of fish resources of the Tehri Dam

Reservoir.

OBSERVATIONS

The effect of Tehri Dam on the Bhagirathi River is more pronounced and has

affected the abundance and distribution of fish species in the river by obstructing their

longitudinal migration. Construction of dam has considerably reduced surface area of

fish habitats to downstream in addition to large destruction of feeding and spawning

grounds of fish dwelling Bhagirathi. Detailed observations on the manifestation of

impact of Tehri Dam on coldwater fish resources of Bhagirathi have been made for a

period of two-year (September 2004 - August 2006).

A. Fragmentation, Isolation and Destruction of Fish Habitats

Substantial transformations in the terms of fragmentation, isolation and

destruction of fish habitats in Bhagirathi River due to the Tehri Dam construction were

observed. Fish were affected adversely by the modification of river morphometry,

velocity, temperature and quality of water. A large scale destruction of fish habitats,

spawning and feeding grounds of fishes was made at the impacted site. A series of civil

construction activities of Tehri Dam contributed towards the severe soil erosion of river

edges and heavy sedimentation. The streambed of the river below the dam was

drastically changed. Due to the stressed environment of the river at the impacted site,

the primary and secondary producers also reduced drastically. As a consequence of the

impoundment, the lotic environment of Bhagirathi was converted into a huge reservoir.

A downstream habitat was altered drastically after the closure of tunnel in October 29,

2005.

B. Removal of Riparian Vegetation

Due to the construction of Tehri Dam, the river edges and riparian corridors

were badly eroded at the impacted site (S2). Embankment at the impacted site became

naked and big boulders replaced the gravels and pebbles. Since riparian vegetation

moderates the water temperature and provides shelter and cover for several fish species

as well as it forms a part of allochthonous food material for fish. Riparian vegetation

was completely submerged upstream after the impoundment, thus reducing the

heterogeneity in the fish habitat.

C. Inundation of Feeding and Spawning Grounds

The inundation of feeding and spawning grounds of coldwater fishes inhabiting

Bhagirathi River was observed at the impacted site (S2) as a consequence of civil

engineering works of Tehri Dam. A large-scale inundation of spawning and feeding

grounds of fish was noticed due to the impoundment. As a result of this, a phenomenal

change in the characteristics of substrate composition and drastic change in turbidity

and silting pattern, the failure of spawning or ineffective spawning of endemic snow

tout and mahseer were observed at the impacted site because the presence of gravel,

pebbles and sand are prerequisite for most of the Bhagirathi fish to build their spawning

nests (redds). Due to the reservoir formation, all the spawning and feeding grounds of

fish were inundated upstream the dam and this has resulted in the reduction of fish

population upstream in the reservoir also.

D. Choking of Migration Channels

Environmental degradation, brought about by intensified dam construction

activities at Tehri, has affected adversely both the migratory and non-migratory fish

species of Bhagirathi. Due to the dam construction activities, the movement of several

fish species has been obstructed. Most influenced fish were the Tor tor, Tor putitora,

Labeo dero and Schizothoraichthys progastus, which migrate from downstream to

upstream for breeding purpose. Local migratory fish were also affected due to the

destruction in their movement through the diverted path of the river during the

construction process of the dam. After the impoundment, the fish route was completely

blocked and thus could not move upstream.

E. Impact of Tehri Dam on Diversity and Distribution of Coldwater Fish in Time

and Space

For the analysis of the impact of Tehri Dam on fish diversity of the Bhagirathi

River, fish species richness, number of species in each community and diversity indices

were taken into account. The earlier study on fish diversity made by Sharma (1984 a)

was also taken in account for comparison of distribution of fish in time and space. The

diversity indices were based on the proportional abundance of fish species in Bhagirathi

River. A total of 23 species belonging to 11 genera and 4 families of fish species were

reported from the Bhagirathi River (Sharma, 1984 a). However, only 19 fish species

belonging to 9 genera and 3 families were found at the reference site (S1) and 12 fish

species belonging to 7 genera and 3 families were recorded at the impacted site (S2)

under the present study before impoundment (Table 6.1). An in-depth survey on the

abundance and distribution pattern of fish species in a big stretch of about 75 km in

Bhagirathi River was also undertaken for analyzing the impact of Tehri Dam

construction. After the impoundment, the fish population of Bhagirathi reduced at both

the sites and a long stretch of Bhagirathi and Bhilangana ecosystems were fragmented

into many zones. The studied stretch of Bhagirathi River was divided into four main

longitudinal zones: Zone A (reference site); Zone B (reservoir); Zone C (impacted

zone) and Zone D (downstream/tailrace zone between Koteshwar and Deoprayag).

Monthly sampling of fish for a period of two-year study revealed that the lowest

number of fish species (04) was found in the periphery of Zone B (reservoir). While,

the maximum number of fish species (17) were found in the Zone D

(downstream/tailrace zone). This maximum fish diversity in Zone D may be due to the

presence of natural fish habitat as well as connectivity of this zone with the Alaknanda

River. A total of 16 fish species were found in the Zone A (reference site) upstream the

Tehri Dam Reservoir. This may be due to the presence of natural habitats to indigenous

fish species in the Zone A. A total 10 fish species were found in Zone C (impacted

zone). Less diversity of fish in the impacted zone may be due to the fact that the

longitudinal migration of high altitude coldwater fishes is obstructed by the structure of

main dam (Table 6.2).

F. Catch Composition of Coldwater Fish

Monthly experimental fishing was undertaken at both the sites (reference;

impacted) through employing the local fisherman for estimating the fish catch

composition. The fishes obtained from the reference site and impacted site were

counted for each species. The catch composition of dominant fish species at both the

sites has been depicted along with the data of Sharma, 1988 (Fig. 6.1). A perusal of fish

catch composition of Bhagirathi recorded a prominent change in comparison to earlier

studies made by Sharma (1988). A significant change was also noticed between the

reference site and impacted site under the present study.

Overall the maximum contribution (57.9 %) to the total fish catch was made by

snow trout (Schizothorax sps) followed by Garra sps (10.3 %), Tor sps (9.1 %) and

Schizothoraichthys progastus (6.3 %) in the natural environment of Bhagirathi

(Sharma, 1988). However, after the deleterious effects of Tehri Dam construction, the

fish composition was altered drastically. Schizothorax sps contribution to the total fish

catch reduced to 19.6 % with the complete disappearance of high altitude migratory fish

species (Crossocheilus latius, Glyptothorax pectinopterus, G. madraspatnam, G. cavia

and Pseudechenies sulcatus) at the impacted site. The contribution of some other

species increased due to disturbance in the natural fish components.

Analysis of fish catch composition at the reference site revealed that the

Schizothorax sps contributed 54.1 % to the total fish catch with the complete absence of

Schizothoraichthys progastus. The mahseer (Tor sps) reduced to 4.0 % with the

negligible contribution of (0.6 %) by Labeo dero. This is due to the blockage of

upstream migration of Tor sps and Labeo dero.

G. Fish Diversity Indices

Diversity indices for fish communities of Bhagirathi River have been computed.

Shannon-Wiener diversity index, concentration of dominance, alpha diversity, beta

diversity, similarity and dissimilarity indices were calculated for this purpose.

Shannon-Wiener diversity indices computed for the fishes dwelling the

reference site (S1) and impacted site (S2) have been presented in Tables 6.3 - 6.6. The

maximum diversity was observed at the reference site (S1). It was found maximum

(2.61) and at the reference site and minimum (1.83) at the impacted site. Thus, it shows

a good water quality at the reference site than the impacted site. However, a reduction

in the Shannon-Wiener diversity indices was also observed in successive years.

Concentration of dominance has also been computed for the fishes dwelling at

the reference site (S1) and impacted site (S2) (Tables 6.7 - 6.10). The concentration of

dominance was observed comparatively high at the impacted site during the study. The

maximum concentration was observed 0.26 at the impacted site and it reduced to 0.09

at the reference site.

The alpha diversity is the total number of species encountered in the study area.

The alpha diversity was recorded maximum (19) in March at S1 and minimum (8)

during August and September months at S2 during first year of observation. It was

found maximum (16) in April at S1 and minimum (6) in February month at S2 during

the successive year of observation (Table 6.11). Beta diversity is a comparison of

diversity between different sites of communities usually measured as the amount of

species and changes between the ecosystems. It was calculated 1.29 between the

reference site and impacted site for the two- year period (Table 6.12).

The degree of taxonomic similarity at both the sampling sites was statistically

tested by calculating the coefficient of similarity and dissimilarity indices. Perusal of

the data revealed that the lower value of similarity index (47.6 %), which indicates the

lesser homogeneity between the two sampling sites. The less similarity between these

two sampling sites indicated the unstability and heterogeneity at both the sampling

sites. The index of dissimilarity (52.4 %) indicated the reverse situation.

t-test has also been calculated between the fish species caught at both the

sampling sites and it has been portrayed in the Table 6.13. The t-stat values for

Schizothorax sps (t = 7.046; p > 0.001), Tor sps (t = 4.138; p > 0.001), Labeo dero (t =

5.557; p > 0.001), Garra sps (t = 3.388; p < 0.01), Barilius sps (t = 3.259; p > 0.01) and

Noemacheilus sps (t = 2.646; p < 0.05) were also calculated for the fish species

dwelling in both the sites. The values of t-stat of these fish species was found to be

greater than the t-critical value of these fish species, thus it shows a considerable as

well significant difference in the density of fish population at both the sampling sites.

H. Impact of Tehri Dam on Snow trout and Mahseer

Study on the impact of Tehri Dam on fish resources was focused on the two

very important and most common fish species snow-trout (Schizothorax richardsonii)

and mahseer (Tor tor and Tor putitora) of Bhagirathi River.

a. Impact on Snow trout

The snow trout is most dominant and economically important fish in upper

Ganges. It contributes about 60-70 % in Alaknanda (Singh, 1993) and 58 % in the

Bhagirathi River (Sharma, 1988). Its local name is ‘maseen’ and its total length ranges

from 10.0 to 35.0 cm in Bhagirathi River during the present study (Fig. 6.4). The

feeding biology of snow-trout (Schizothorax richardsonii) revealed that it is

stenophagic herbivorous bottom feeder. The basic food of snow-trout comprised of

green algae, blue-green algae and diatoms and it feeds on this basic food mainly during

winter during its abundant availability in nature. The secondary food comprised of

macrophytes and the obligatory food is sand and detritus and it feeds on this food

during monsoon when there is scarcity in basic food. The feeding intensity of snow-

trout has two peaks a year, the first being in February and the second in November. The

change in feeding intensity appeared to be related with the availability of food items in

the Bhagirathi River (Sharma, 1983). The spawning biology of snow-trout revealed that

it has two spawning periods in a year, one in February-march, while the other in

September-October. Snow trout is non-migratory fish. It moves locally in the river in

search of food and prefers only cold water.

During the construction of Tehri Dam, the hydrology and the morphometry of

the river transformed, which adversely affected the distribution of snow trout in

Bhagirathi. It could not find proper feeding and spawning habitat downstream the Tehri

Dam due to the stressed environment and scarcity of food. Thus, the density of snow-

trout reduced at the impacted site. After the closure of the tunnel (T-2), the fish could

not find its way to move across the Dam. Thus, the number of the snow-trout declined

sharply at the impacted site (S2) after impoundment. The water level reduced to very

low at the impacted site after the closure of tunnel. The snow-trout population also

declined in the reservoir after the impoundment. It was difficult for snow-trout to thrive

in the deep, stagnant and oxygen deficient water of the reservoir. However, few

individuals were found in the periphery of the Tehri Dam Reservoir. Most of the

individuals of snow-trout preferred to move upstream in search of natural environment

(reference site). Therefore, snow-trout was found in good number at the reference site,

which did not receive any impact of the Tehri Dam.

Impact on Production of Snow-trout

Production components like density - N (number of individuals 1000 m-2), mean weight

of a specimen - w (g), mean biomass - B (g m-2), growth rate - G, monthly production

- P (g m-2 month-1) and annual production (g m-2 yr-1) for snow-trout estimated at the

reference site (S1) and impacted site (S2) over a two-year period (September 2004 -

August 2006) have been presented in Tables 6.14 - 6.15.

Biomass (Standing Crop) of Snow-trout ( B ):

The maximum mean biomass (2.550 g m-2) of snow-trout was found to be at the

reference site in the month of February and minimum (0.180 g m-2) in the month of

August during the first year of study period. However, the maximum mean biomass

(1.118 g m-2) of snow-trout was observed in March and minimum (0.102 g m-2) in the

month of August at the impacted site.

During the second year of study, (September 2005-August 2006), the maximum

mean biomass (2.889 g m-2) of the snow-trout was observed during the month of March

and minimum (0.157 g m-2) during August at the reference site. While, the maximum

mean biomass (0.776 g m-2) of snow-trout was found in February and minimum (0.080

g m-2) in August at the impacted site.

Growth of Snow-trout (G):

A positive growth of snow-trout was observed during autumn (September -

October), winter (November - February) and early summer (March - April) in natural

environment (S1) showing density dependent trend. The growth showed the decreasing

pattern in late summer (May - June) and in the monsoon months (July - August), when

lotic environment of the Bhagirathi was turbid with a sparse population of primary

(periphyton-phytoplankton) and secondary (macroinvertebrates) producers due to the

melting snow at the higher reaches during summer and flash floods during the monsoon

months. During these months, the density-dependent trend of snow-trout growth was

disturbed under the severe environmental pressure.

At the impacted site, the same trend in growth of snow-trout was observed

during the first year of study. However, a positive growth was observed from October

till February and after that the growth showed a negative trend upto the month of

September during the second year of study. This may be due to the closure of tunnel (T-

2) resulting in the reduction in the density of snow-trout and allocthonous material at

the impacted site, which forms the part of food for fish species when primary and

secondary producers are less available for them.

Production of Snow-trout (P):

The high production of snow-trout was estimated to be at the reference site (S1)

during winter (November - February) and early summer (March - April) during its high

density. The negative production was also estimated during the late summer (May -

June) and monsoon months (July - August), when the low density of the snow-trout was

observed. Monthly production of snow-trout reduced to a greater extent at the impacted

site (S2) during both the years. This may be due to the low density of snow-trout at the

impacted site due to the dam construction activities.

The annual production of snow-trout was observed 0.921 g m-2 yr-1 at the

reference site and it reduced to 0.382 g m-2 yr-1 at the impacted site during first year of

observation and in the successive year it was observed 0.898 g m-2 yr-1 at S1 and 0.207 g

m-2 yr-1 at S2. A sharp decline in the annual production of snow-trout was observed at

the impacted site (S2) than the reference site (S1) during study period.

A comparison of the present estimation of the impact of Tehri Dam on the

annual production of snow-trout with the earlier study made by Sharma (1991) revealed

a substantial reduction in the production of snow-trout at the impacted site (0.295 g m-2

yr-1) from the earlier study (0.405 g m-2 yr-1). However, no marked difference in the

production of snow trout at the reference site was noticed (Fig. 6.2).

The multiple regressions among the abiotic parameters and production of snow-

trout have been calculated (Tables 6.18 – 6.19). The same was also calculated between

production of snow-trout and other biotic components of Bhagirathi River (Tables

6.22).

b. Impact on Mahseer

The mahseer contributes about 6.67-13.33 % (Singh, 1993) in Alaknanda and

9.14 % in Bhagirathi River (Sharma, 1988). It shows that it does not form a big share to

the total fish catch of upper Ganges. But, the mahseer is one of the most important and

mighty sport fish of the country. Britishers used to be the royal guest of the then ruler of

Tehri State for angling pleasure of mahseer in the Bhagirathi during pre-independent

period. Locally, it is known as ‘dansula’ and ‘mahseer’ (Fig. 6.5). Mahseer weighs upto

23 kg in the River Bhagirathi (Sharma, 1981). The adults ranged from 22.0 to 75.5 cm

and juveniles from 9.8 to 21.2 cm in total length in Bhagirathi River (Sharma, 1987).

The adults of mahseer (Tor tor and Tor putitora) are euryphagic omnivorous column

feeder and the juveniles are filter feeders. The basic food of adult Tor tor constitutes

insects and their larvae, crustacea, algae, diatoms and protozoa. The macrophytes form

the secondary food and other food items such as rotifers, shell parts of mollusca and

fish parts form the accidental food. The sand and detritus constitute the obligatory food

of Tor tor (Sharma, 1986). The basic food of adult Tor putitora constitutes fish matter,

larval, nymphal and part of adult stages of aquatic insects and algae. The crustaceans

and their larvae, protozoa, rotifers and diatoms comprised the secondary food. The

pieces of molluscs shells and other unidentified matter of animals serves as the

accidental food and fragments of macrophytes, sand and detritus were observed to form

obligatory food (Sharma, 1987). The feeding intensity of mahseer attains two peaks,

first being in July during post-spawning period and the second in December when

plenty of phytoplankton were present in the river. Since, adult mahseer remain present

in Bhagirathi River only after March till August-September. These fish species ascend

the Bhagirathi in order to spawn in March, as the breeding period commences from

March to June. Mahseer migrates from foothill to the upper reaches for spawning is

possibly due to the high temperature of water in foothills in which the delicate fish do

not prefer to breed. After this, the adults move back, only juveniles and small fish were

found in Bhagirathi in winter. The mahseer is migratory fish and migrates upstream in

the Bhagirathi from foothills in March for breeding and moves back after August-

September on the onset of winter. This fish cannot tolerate very hot and very cold

water. Thus, when the water temperature rises in foothills it migrates to upper reaches

and as the temperature start lowering in upper reaches then it moves back to its own

place.

Mahseer population declined in the entire stretch of the Bhagirathi River due to

the changes in the hydrological regime during the construction of Tehri Dam and after

impoundment. Mahseer were caught at the reference site during the first year of study.

Adult mahseer were caught during March onwards till August-September and after that

the only juveniles were caught. During the second year, it was found till January at the

reference site after that because of the closure of the tunnel these fish were unable to

reach upstream the dam. Mahseer were caught during both the years at the impacted site

but their density was low due to the stressed environment, poor shelter, less availability

of the food and poor water quality. After the completion of Tehri Dam and blockade of

the river, the water level reduced downstream. The natural flow of river has changed

with almost constant water level downstream throughout the year. The earlier existing

feeding and spawning grounds were lost due to the sharp reduction in the water level

and flooded area downstream the Tehri Dam. Due to massive morphometric

transformations at the impacted site, the density of mahseer declined downstream after

impoundment.

Impact on Production of Mahseer

Production components like density - N (number of individuals 1000 m-2), mean

weight of a specimen - w (g), mean biomass - B (g m-2), growth rate - G, monthly

production - P (g m-2 month-1) and annual production (g m-2 yr-1) for mahseer estimated

at the reference site (S1) and impacted site (S2) over a two-year period (September 2004

- August 2006) have been presented in Tables 6.16 - 6.17.

Biomass (Standing Crop) of Mahseer ( B ):

The maximum mean biomass (0.252 g m-2) of mahseer was estimated at the

reference site in the month of May and minimum (0.030 g m-2) in the month of

December during first year of study period (September 2004-August 2005). However,

the maximum mean biomass (0.224 g m-2) of mahseer was observed in May and

minimum (0.025 g m-2) in the month of December at the impacted site. The maximum

mean biomass during summer months (March-June) at S1 and S2 may be due to the high

density of mahseer found during these months in the Bhagirathi River than in the winter

months when only few juveniles of mahseer were caught.

During the second year of study (September 2005-August 2006), the maximum

mean biomass (0.224 g m-2) of the mahseer was observed during the month of October

and minimum (0.045 g m-2) during January at the reference site. However, the

maximum mean biomass (0.209 g m-2) of mahseer was found to be during May and

minimum (0.020 g m-2) during November at the impacted site. Mahseer were not found

after January, 2006 due to the closure of tunnel (T-2) on October 29, 2005 at the

reference site. Only one or two individuals were caught at the reference site between the

closure of tunnel and January 2006.

Growth of Mahseer (G):

At the reference site, a positive growth of mahseer was observed from January

till May. The growth showed the decreasing pattern from June till December. Growth

was found positive in late winter (January - February) and in summer (March - May)

due to the availability of large amount of food material for them during these months.

During second year, the mahseer showed the irregular growth due to the disturbance

caused by the closure of the tunnel.

At the impacted site, same trend was found during the first year of observation.

The positive growth of mahseer was observed from January to May during the first year

and from December to May during the second year. The growth showed a negative

trend in June and in monsoon season (July - August) due to food scarcity during these

months.

Production of Mahseer (P):

During the first year of study, the positive production of mahseer was observed

from January to May at the reference site (S1) and impacted site (S2). A negative

production was observed at both the sampling sites during rest of the months.

Production of mahseer was not found to be highly dependent on the density in both the

sampling sites.

During the second year, the positive production was found during September

and October at the reference site (S1), whereas at the impacted site (S2) the production

showed the positive value during winter months (December - February) and summer

(March - May). At the reference site, mahseer were not found after January, thus the net

production was contributed by mahseer found only during five months (September -

January).

The annual production of mahseer was observed to be 0.129 g m-2 yr-1 at the

reference site and it reduced to 0.053 g m-2 yr-1 at the impacted site during first year of

observation. However, the density of mahseer was more at the impacted site than the

reference site. Production of mahseer was observed to be 0.009 g m-2 yr-1 at S1 and 0.24

g m-2 yr-1 at S2 during second year of study. The production of mahseer reduced

drastically at S1 during the second year due to the obstruction in the movement of

mahseer from reaching at the reference site.

A comparison of the present estimation of the impact of Tehri Dam on the

annual production of mahseer with the study made by Sharma (1991) revealed a sharp

decline in the mahseer production at the reference site (0.069 g m-2 yr-1) from the earlier

study (0.161 g m-2 yr-1). However, the impacted site did not show any considerable

change in the production of mahseer (Fig. 6.3).

The multiple regressions among the abiotic parameters and production of

mahseer have been calculated (Tables 6.20 - 6.21). The same was also calculated

between production of mahseer and other biotic components of Bhagirathi River

(Tables 6.23).

I. Impact on Downstream Fish Resources

A marked impact on the downstream fish resources or tailrace fish resources

was also noticed. A total of 12 fish species out of 19 (reference site) were found at the

impacted site during the first year of study. The reduction in the fish population

downstream the Tehri Dam before impoundment was due to the modified fluvial

system, improper feeding and spawning grounds, reduction in the density and

production at the primary and secondary trophic levels, eroded embankment,

transformed streambed, high turbidity, low transparency, low dissolved oxygen, high

free carbon dioxide and obstruction in the movement of fish.

After the closure of the tunnel and formation of the reservoir, the number of

fish species also reduced and reached to 10 at the impacted site. This was due to the

complete blockade of the fish route and the fish could not reach downstream. The

creation of reservoir modified the downstream water flow regime and affected the fish

assemblages drastically. It reduced the flooded areas where fish reproduce and juveniles

find food and protection from the predators. Thus, the fish species richness declined

below Tehri Dam in comparison to the unregulated river. The water level reduced to

very low (minimum 10 cm) immediately after the closure of tunnel for two months

(November and December). During these two months, fish habitats were destroyed

completely downstream the Tehri Dam. Due to reduction in water level, the turbidity

increased considerably and the dissolved oxygen reduced significantly forcing the fish

for struggling for their survival in the stressed environment. A mass mortality of fish

population was observed during this period. Later on at the end of December, sufficient

water was released from the reservoir. But the downstream water lost its natural flow

regime along with the allochthonous food. Thus, the fish resources were affected

adversely downstream due to the Tehri Dam and the impoundment of Bhagirathi. Fish

were affected directly by blockade of longitudinal migration, irregular releases of water

from dam and periodic inundation or drying out of spawning grounds and refuge

downstream the Tehri Dam.

J. Cumulative Impacts of Tehri Dam Construction

The consequences or cumulative/ synergistic impact of Tehri Dam construction

on the fish resources of Bhagirathi River can be presented in terms of direct impacts or

primary effects, indirect impacts or secondary effects and cumulative and synergistic

impacts or ecological consequences (Fig. 6.6). The major cause and effects of Tehri

Dam construction were rock stripping, digging of tunnels, construction of approach

roads, coffer dam, main dam and dumping of huge muck in the Bhagirathi watershed.

Direct impacts or primary effects were the major geomorphometric transformation of

fluvial system, drastic alteration in the composition of bottom substrata, degradation of

water quality, inundation of feeding and spawning grounds of fish, choking of

migration channels and massive removal of riparian vegetation. Indirect impacts or

secondary effects do not have direct impacts on fish resources but are the consequences

of direct impacts. These indirect impacts of Tehri Dam include the fragmentation of

fish habitats, habitat isolation and shrinking of population of the fish food (periphyton,

phytoplankton and aquatic macroinvertebrates). The cumulative and synergistic impacts

are generally the consequences of single impact, multiple interrelated impacts or

multiple unrelated direct and indirect impacts. The cumulative and synergistic impacts

of Tehri Dam were manifested in the form of impairment of ecosystem function, loss of

fish diversity and reduction in fish production under ecological stress.

DISCUSSION

Changes due to dam construction in downstream site are more sudden,

conspicuous and frequently dramatic which causes the decline in the density and

diversity of fish (Petts, 1984). In the present study, a drastic reduction in the density as

well as diversity of fish species was observed at the impacted site (S2). A significant

reduction in fish diversity of Bhagirathi River has been assessed during a period of

twenty-year (1984-2004). The number of fish species reduced from 23 (Sharma, 1984

a) to 16 (reference site). Only 10 fish species were found to be at the impacted site as a

consequence of Tehri Dam construction. The study on fish catch composition revealed

that Schizothorax sps contributed the major fisheries of snow-fed river having highest

percentage in the catch (54.1 %) at the reference site, which may be due to the low

water temperature and high dissolved oxygen in the Bhagirathi River. Jhingran (1982)

has also reported that the Schizothorax sps prefer a low temperature (8.0 – 22.0 0C).

Abundance of other Bhagirathi fish species also depends on their responses to the

environmental conditions of the river and habitat diversity. Sharma (1988) studied the

catch composition of the Bhagirathi fishes and found that the abundance of

Schizothorax sps was 57.9 %, which was due to the presence of low temperature, high

contents of dissolved oxygen and alkalinity of Bhagirathi water. Schizothoraichthys

progastus contributed 6.3% to the total fish catch. However, Tor sps, Labeo dero,

Garra sps, Barilius sps, Noemacheilus sps and Crossocheilus latius contributed 9.1%,

2.8%, 10.3%, 2.1%, 2.5% and 2.5% respectively to the total catch in Bhagirathi

(Sharma, 1988). The catch contribution of Schizothorax sps reduced drastically to 19.6

% to the total fish catches under the present study. Crossocheilus latius, Glyptothorax

sps and Pseudecheneis sulcatus were completely missing from the present fish

composition spectrum of Bhagirathi under the present study. However, the contribution

of other fishes to the total fish catch of Bhagirathi was prominently disturbed at the

impacted site (Fig. 6.1).A negative impact on snow-trout (Schizothorax) and rohu

(Labeo) in Himalayan streams has been reported by Sandhu and Toor (1984) as a

consequence of construction of Bhakra and Nangal Dam. Sandhu and Toor (1984) also

observed a sharp decline in the catches of Hilsa ilisha as a result of dams, barrages,

weirs and anicuts on the Hoogly, Godavari, Krishna and Cauvery Rivers. They reported

that the mahseer (Tor tor and Tor putitora) did not show their presence upstream

Nangal and Talwara dams in India. The mahseers are migratory fish and they migrate

upstream from the foothills upto the Tehri Dam site via Deoprayag in March and stay in

the coldwater upto September. The mahseer also avoids too coldwater during winter

and go back to foothills during the onset of winters. The mahseer was observed at the

reference site during the first year of observation, as few of them were able to found

their way through the tunnel. However, after the closure of the tunnel on October 29,

2005, only one or two fish species were caught at the reference site till January and

thereafter no mahseer was found at the reference site. At the impacted site, these fish

species were caught throughout the study period but in very less number due to the

complete transformation of fluvial system into the reservoir.

Labeo dero is also a migratory fish and ascends upstream for spawning purpose

during the onset of summers and go back to foothills during the onset of winter

(Sharma, 1984 d). Glyptothorax sps and Pseudecheneis sulcatus are high altitude

migratory fishes. These fishes migrate from higher elevations to lower reaches near

Tehri town for spawning purpose (Sharma, 1984 b, c). These fish species move right

from May upto the end of October from Harsil to Tehri and were not found during

winter months at the reference site (S1). These two fishes were not found at the

impacted site during the study. Garra sps are not the migratory fish and were mainly

abundant during the winter months when plenty of food was available in the Bhagirathi

(Sharma, 1990).

Due to the diversion of river water through the tunnels, the longitudinal

movement of the Bhagirathi fishes was obstructed. Shannon- Wiener diversity index

reduced from 2.61 to 1.83 during a span of two-year study. This may be due to the

blockade of migration channel of fishes in Bhagirathi. Edwards (1978) also found a

reduction in fish species diversity compared to pre-impoundment records, in Texas

River. Four species of cyprinids which were present in a river upstream from an

impoundment in Canada, were absent below the dam, although some other species

greatly increased in abundance in the tailwaters (Spence and Hynes, 1971). Our

observation on Tehri Dam is supported by the works of Ward and Stanford, 1983; Petts,

1984; Angermeier et al., 1986; Ney and Mauney, 1981; Penczak et al., 1984; Erman,

1986; Rasmussen, 1986; Garcia de Jalon et al., 1994; Koryak and Hoskin, 1994;

Martinez et al., 1994; Kubecka and Vostradovsky, 1995; Lusk, 1995; Travnichek et al.,

1995 and Penczak et al., 1998. All these workers reported decline in species richness

caused by dam construction. Similarly, Vimba vimba practically disappeared from

commercial catches in the upper reaches of the Vistula and the Dyje Rivers in Poland

after dams had been constructed (Backiel, 1985 and Lusk, 1995).

Fish resources upstream the Tehri Dam was also affected adversely. Only few

coldwater fish species were found in the periphery of reservoir after the impoundment.

It clearly indicates that the riverine fish species were not able to thrive in such a

modified environment (deep lentic environment). In Columbia River System, the

population of Acipenser transmontanus, an endangered fish species has reduced in the

reservoir than the unimpounded part because of control of floods and creation of

homogenous conditions in the reservoirs, reduced habitat diversity and prevention of

movement of fish from different riverine habitats (Baemesderfer et al., 1995 and Geist

et al., 1996). As a ‘migrating barrier’ a dam may preclude the movement of riverine

fish in both directions, if it has neither fishways nor ‘ecological turbines’ in

hydroelectric power-dams (Petts, 1984 and Orth and White, 1993). Tor tor, T. putitora

and Labeo dero disappeared from the reference site after the closure of the tunnel under

the present study on Tehri Dam. The same observation was made in Nepal where the

existing dam on Tinau River put the negative effect on migratory fishes (Bagarius

bagarius, Labeo angra and Tor tor). Bagarius bagarius and Labeo angra have

completely disappeared from upstream the dam (Jha et al., 2001). Dams block upstream

spawning and migration, and the impoundments reduce the area of stream substrates

available for spawning. Zhong and Power (1996) reported that the number of fish

species decreased from 107 to 83 as the fish migration was interrupted by Xinanjiang

Dam (China). Quiros (1989) also reported the disappearance of the fish species in the

upper reaches of Latin American rivers after the dam construction. The change in

habitat caused by the construction of a dam modified the fish community, population

densities and the area utilized by a particular species (Horwath et al., 1998). The

building of a dam generally has major impact on fish populations, migrations and local

movement of fish. The movements can be stopped or delayed in addition to the

obstruction of the accessibility of the natural habitats. Fish can inflict major damage

during their transit through hydraulic turbines or over spillways.

Vegetation cover plays an important role in regulating stream flow and

maintaining water quality in providing cover for many fish species and in serving as an

essential source of allochthonous food for fish in otherwise nutrient-poor waters

(Sharma, 1992). Thus, its absence or removal can therefore produce a number of

negative effects on aquatic organisms. Large scale destruction of vegetation cover was

observed under the present study. It has deleterious impact at the impacted site (S2).

Philip (1931) has opined that the large scale removal of vegetation from the river banks

have deleterious effects on the growth of trout, because their removal tends to rise water

temperature and affects the occurrence and abundance of fish food. Increased water

velocity can cause a correspondingly larger proportion of the substratum to be

transported and scoured, dislodging a large number of fish eggs, benthic organisms and

affecting the fish (Petr, 1983).

One of the major effects of the construction of dam on fish populations is the

blockade of the upstream migration of fish species. This can ultimately lead to the

extinction of few species upstream the dam. The decline in the stocks of diadromous

species was observed in France. Obstruction of the fishway was also responsible for the

extinction of the entire stocks (Salmon in the Rhine, Seine and Garonne rivers) and also

for the confinement of certain species to a very restricted part of the river basin (Salmon

in the Loire, Shad in the Garonne and Rhine, etc.) (Porcher and Travade, 1992).

Sturgeon stocks have been particularly threatened by hydroelectric dams on the Volga,

Don and Caucasian Rivers (Petts, 1984). The extinction or the depletion of migrating

species such as salmon and Shad on the Connecticut, Penobscott and Merrimack rivers

was observed on the East Coast of USA by the building of dams (Baum, 1994; Meyers,

1994 and Stolte, 1994). These are the long term impacts of impoundments. The process

of extinction is possible in case of the present study, as it is an impoundment of only

one year.

Impoundment has inundated the spawning and feeding grounds of the fish

upstream the Tehri Dam. About 40% of the spawning grounds in the Quintang River

above the Funchunjiang dam were lost by flooding (Zhong and Power, 1996). On the

Columbia River, and its main tributary the Snake River, most spawning habitat were

flooded due to the construction of dams creating an uninterrupted series of

impoundments (Raymond, 1979). Regulation of stream flow during the migratory

period can alter seasonal and daily dynamics of migration. Regulation can lead to a

sharp decrease in a migratory population, or even to its complete elimination. Any

reduction in river discharge during the period of migratory activity can diminish the

attraction potential of the river, hence the number of spawners entering the river is

reduced. Natural spawning grounds have been lost, especially for mahseer and for

commercially important species in the upper and lower Indus plains (Asianics Agro-

Dev, 2000). The catches of migratory fish, such as Palla and Barramundi have

significantly decreased by the construction of the barrages at Kotri and Sukkur.

The Tehri Dam and the impoundment of Bhagirathi have transformed the

geomorphology of the river and destroyed the natural habitats of several fish species. It

has caused a shrinking in the population of most of the fishes dwelling Bhagirathi.

However, the present work was focused on the impact of Tehri Dam on the production

of Snow-trout and Mahseer.

The mechanisms controlling the levels of fish production in rivers are still

poorly understood (Mann and Penczak, 1986). Abiotic factors, especially floods, appear

to determine the population densities in many head-water habitats (Crisp et al., 1975;

Waters, 1983 and Penczak and Molinski, 1984). But the potential maximum production

in such waters may be under biotic control, chiefly through the levels of autochthonous

and allochthonous food resources, which regulate growth rates, though even these

variables may be under abiotic influence (Waters, 1983). Specialization in stream fish

communities occur primarily in selection of specific habitat types and secondary in

preference for food resources (Gorman and Karr, 1978), the total niche space occupied

depends on range of aquatic habitat available for shelter, reproduction and foraging, and

on the quality and variety of potential food resources.

The density dependent regulation of fish growth can be disturbed in degraded

environment induced by anthropogenic perturbations (McFadden and Cooper, 1964).

The regulatory processes in the fish communities are considered to be different in

juvenile forms which under environmental pressure respond mainly by mortality and

mature specimens which respond by growth retardation (Backiel and Le Cren, 1978).

The present study on the impact of Tehri Dam on the production of snow-trout

and mahseer revealed that the growth of snow-trout in the Bhagirathi was density-

dependent process during the period of positive growth (Tables 6.14 - 6.15). However,

no marked density-dependent regulation of growth of mahseer was noticed (Tables 6.16

- 6.17). Thus, it was inferred from the present study that the mahseer is more sensitive

to environmental degradation than the snow-trout, as environmental variables

dominates on the density-dependent process in regulating the mahseer growth. In

Baram River, low nutrient load, high flushing rate, extreme fluctuations in flow regime

and high turbidity have probably eliminated primary productivity as a major food

resources for fish communities in the river (Watson and Balon, 1984). According to

Power (1973) the presence of cover in the form of boulders and large stones greatly

enhances the holding capacity of the rivers for fish and hence, influence the production

level. Aquatic plants are important habitats for fish because they increase spatial

heterogeneity and feeding resource availability (Thomaz et al., 1999).

The annual production of snow-trout reduced significantly as a consequence of

Tehri Dam construction within a period of two-year. It declined from 0.921 g m-2 yr-1 to

0.207 g m-2 yr-1 (Table 6.14 – 6.15).

The annual production of mahseer also declined drastically due to Tehri Dam

construction. It declined from 0.129 g m-2 yr-1 to 0.009 g m-2 yr-1 during a span of two-

year (Table 6.16 – 6.17).

Production levels are determined by abiotic and biotic factors, with the former

of greater importance in relatively unstable habitats whereas, habitat diversity, extent of

cover and food resources have an increased relevance on more benign habitats (Mann

and Penczak, 1986). Some evidences that the continual changes of riverine environment

are reflected in basic fish population properties as growth (Skora and Wtodek, 1971 and

Welcomme, 2006) and productivity (Allen, 1951). The productivity is a basic parameter

necessary to understand the functioning of an ecosystem (Zalewski et al., 1985).

Multiple regression gives the idea of significant relationship of snow-trout with

the different environmental variables of Bhagirathi river at both the sampling sites

(Tables 6.18 - 6 .19). At the reference site (S1), a significant relationship of snow-trout

was found with air temperature (r = -0.694; p > 0.01), water temperature (r = -0.752; p

< 0.01), water current (r = -0.604; p > 0.01), hydromedian depth (r = -0.554; p > 0.05),

turbidity (r = -0.433; p > 0.05), total dissolved solids (r = -0.502; p > 0.05), dissolved

oxygen (r = 0.812; p = 0.001), free CO2 (r = -0.564; p > 0.05), pH (r = -0.649; p > 0.05)

and nitrates (r = -0.744; p > 0.001). Almost the same relation was found at the impacted

site (S2) with air temperature (r = -0.744; p > 0.001), water temperature (r = -0.680; p >

0.01), water current (r = -0.699; p > 0.01), hydromedian depth (r = -0.518; p > 0.05),

turbidity (r = -0.542; p > 0.001), total dissolved solids (r = -0.413; p > 0.05), dissolved

oxygen (r = 0.521; p > 0.01), free CO2 (r = -0.579; p < 0.05), chlorides (r = -0.650; p >

0.01), nitrates (r = -0.609; p < 0.05) and phosphates (r = -0.567; p > 0.05).

In the present study, the highly positive correlation was observed between the

production of snow-trout and the zoobenthos (r = 0.758 and p > 0.001), zooplankton (r

= 0.756 and p > 0.001) and periphyton-phytoplankton (r = 0.648 and p < 0.05) at the

reference site and similar relationship was observed at the impacted site (zoobenthos: r

= 0.572 and p > 0.05; zooplankton: r = 0.705 and p < 0.01 and periphyton-

phytoplankton: r = 0.655 and p < 0.05) (Table 6.24). The high fish biomass and

productivity in upland streams was attributed to a high nutrient load converted into

primary productivity (Allen, 1951; Oglesby, 1977; Penczak, 1981 and Zalewski and

Penczak, 1981).

Similarly, the multiple regression between the production of mahseer and

abiotic variables at both the sampling sites has been given in the Tables 6.20 - 6.21. The

mahseer production was found to be influenced by air temperature, water temperature,

water current, hydromedian depth, turbidity, total dissolved solids, dissolved oxygen

and free CO2 at the reference site and the impacted site. Mahseer do not favour very

cold water thus, on the onset of winter these fish species move back to their original

place and due to which low number were recorded during winter than the summer

season in the Bhagirathi River. Thus, the production of mahseer was found to be

positively correlated with the air temperature (S1: r = 0.479; p > 0.5 and S2: r = 0.481; p

> 0.5) and water temperature (S1: r = 0.455; p > 0.5 and S2: r = 0.495; p > 0.5).

A positive correlation of mahseer production was observed with the zoobenthos

(r = 0.169), zooplankton (r = 0.109) and periphyton-phytoplankton (r = 0.372) in the

natural environment and the same was observed at impacted site (zoobenthos: r =

0.193; p > 0.5; zooplankton: r = 0.629; p < 0.5 and periphyton-phytoplankton: r =

0.637; p < 0.5) (Table 6.23). But a good significant relation was not found between

mahseer production and other biotic variables.

In the present study on fish (snow-trout and mahseer) production influenced by

the Tehri Dam construction activities, it seems acceptable the regulation of production

by abiotic (increased turbidity, total dissolved solids, degradation of feeding and

spawning grounds, blocking of migration channels, choking of breeding grounds and

extensive destruction of covers for fish) and biotic (food resources: primary and

secondary producers) factors. Thus, the depletion of production of snow-trout and

mahseer seems understandable as a consequence of construction activities of the Tehri

Dam.

Penczak (1981) has found the highest fish production in two Polish rivers to be

at sites with the lowest numbers of species, the maximum production (807 kg ha-1 yr-1)

occurring in a headstream section with just three species. Riparian vegetation plays an

important ecological role in stream ecosystems, especially in headwater reaches, by

providing cover for stream fishes, by reducing bank erosion, and through its influence

on stream temperature (Ward, 1982). Raymond (1979) attributed a nearly one-month

delay in downstream migrating juveniles to the construction of dams on the Snake

River, major tributary of the Columbia River. Screens may be installed to prevent

juveniles from passing through the turbines, and spillway deflectors and other devices

are available to reduce losses from gas bubble disease (Wietkamp and Katz, 1980).

According to Mann and Penczak (1986), productivity levels of fish are under

both biotic and abiotic influence, with the latter being of prime importance in many

upland waters. Biotic variables (food, cover and predation) have more influence in

stable environments, although physical parameters, especially water temperature, can

still play a major role in determining the characteristics of local fish populations.

Zalewski and Naiman (1985) demonstrated that abiotic factors (fluvial geomorphology,

geology and climate) were of primary importance in many situations, but where the

environment becomes stable or predictable, the role of biotic factors (competition,

predation, productivity) gradually increases in importance. Zalewski et al., (1985)

stressed that growth rates in headwaters (low order streams) are primarily restricted by

abiotic factors, especially temperature and trophic status, however, they are to a large

extent modified by density-dependent regulation and intraspecific competition.

A drastic reduction in the food resources of fish communities was noticed at the

impacted site (S2) than the reference site (S1). A considerable reduction in the density of

periphyton-phytoplankton (primary producers) was observed at the impacted site (255.0

± 126.38 units l-1) than the reference site (530.54 ± 285.80 units l-1) over two-year of

the study period. A detrimental effect of Tehri Dam construction was also noticed in the

secondary producers (macroinvertebrates) at the impacted site (172.92 ± 171.45 units

m-2) as compared to the reference site (895.83 ± 623.70 units m-2). Thus, it seems

logical to accept the contention of depletion in the fish production (snow-trout and

mahseer) influenced by the sharp diminution in the primary and secondary producers in

the stressed environment (S2) of the Bhagirathi. Changes in the trophic status of water

bodies can affect the growth of fishes (Bayne et al., 1991; Treasurer and Owen, 1991;

Lieu et al., 1994). Difference in the growth rate is associated with food abundance and

quality (Potts and Khumalo, 2005).

Fish production which is tightly linked to fish growth, shows close dependence

to levels of primary production (Goodyear et al., 1972; Melack, 1976 and Boyd, 1979).

In southern Africa, both Tomasson and Allanson (1983) and Merron and Tomasson

(1984) noted that a depression of the trophic resource base in Lake Le Roux resulted in

a cascading effect through food web, ultimately resulting in decreased growth and

production of larger cyprinid species. Fish production is directly influenced by fish

growth, which in turn is dependent largely on food ingested (Welcomme, 2001 and

Potts and Khumalo, 2005).

The assessment of impact of Tehri Dam construction and impoundment

revealed that the most influenced element was coldwater fishery of Bhagirathi upstream

as well as downstream the dam. The suppression of flood regime downstream from an

impoundment by means of flow regulation can deprive many fish species of spawning

grounds and valuable food supply (Petts, 1984). This can lead to changes in species

composition with the loss of obligate floodplain spawners. From the study of the

threatened fish in Oklahoma, Hubbs and Piggs (1976) suggested that 55% of the man-

induced depletion has been caused by the loss of free flowing river habitat resulting

from flooding by reservoirs, and a further 19% of the depletion was caused by the

construction of dam, acting as barrier to fish migration. On the Indus River, the

construction of the Ghulam Mohammed Dam has deprived the migratory Hisa ilisha of

60% of their previous spawning areas (Welcomme, 1985).

Dams create such hydrological conditions, which young fish cannot tolerate

(Ponton and Vauchel, 1998). Flow regulation has been found to affect fishes inhabiting

shallow water areas more than those in deep water (Travnichek and Maceina, 1994).

This has been attributed to a reduction in species adapted to fluvial conditions. Fluvial

species have been found to increase on longitudinal gradient downstream from a dam.

No spatial gradient existed for those fishes with a more generalist habitat preferences

(Kinsolving and Bain, 1993). In Tennessee River System, tailwaters below dams did

not provide suitable areas for reproduction of native fish and the diversity also declined

(Neves and Angermeier, 1990). Also, in the South Fork Holston River 43 species were

found before impoundment compared to 17 species collected in the tailwater of the

operating dam. Thirty two species were sampled before construction of the Watauga

and Wilbur Dams compared to 13 species in the tailwaters after impoundment (Neves

and Angermeier, 1990). Dams in Australia have caused habitat degradation, blocking

passage (migrations) preventing dispersal and re-colonization of previous habitats, loss

of dry weather stream flow and suppression of flooding (Wager and Jackson, 1993).

In USA, in Columbia Riverine System, the mortalities of upstream (adult

mortality 37-51%) and downstream (juvenile mortality 77-96%) migrants at dams are

one of the main causes of the declines in anadromous fishes. And also more than 200

stocks of anadromous salmonids have become extinct (Nehlsen et al., 1991;

Independent Scientific Group, 1999). In Colorado Riverine System, the nursery habitats

of Ptychocheilus lucius (Colorado squawfish) in the Green River catchment disrupted

probably because of extreme flow fluctuations and alteration of seasonal flow regimes.

In the White River, the Taylor Draw Dam blocked the migration of the squawfish

(Carlson and Muth, 1989; Martinez et al., 1994 and Stanford and Nelson, 1994).

In French Guiana, in Sinnamary River, there was observed the flow reduction

in river as a result of the dam caused a decrease in the number of taxa of juveniles from

51 to 48 downstream the dam. Also species richness was decreased from 54 to 47 after

the construction of dam (Ponton and Copp, 1997; Sugunan, 1997; Ponton and Vauchel,

1998; Merona and Albert, 1999; Sugunan, 2000 and Kouamelan et al., 2003).

The above in-depth study on the impact of Tehri Dam on the coldwater fish

resources and discussion in the light of works done on other dams concluded that the

Tehri Dam has several direct impacts and indirect impacts on the aquatic environment

and the fish resources of Bhagirathi River. The over all cumulative and synergistic

impact of the Tehri Dam manifested in the form of shrinking of population of natural

fish foods (phytoplankton, periphyton, zooplankton and benthic macroinvertebrates)

due to degradation of water quality. All these impacts have ultimately caused the

depression in the diversity, percentage contribution of individual fish species and

production of coldwater fishes especially snow-trout and mahseer dwelling Bhagirathi

River. Therefore, it is an urgent requirement for undertaking ameliorative measures for

the protection and restoration of coldwater fish species.

Table 6.1. Impact analysis of Tehri Dam on fish diversity in the area of Tehri Dam Project

Present Study (2004-06)

S.No. Fish species

Sharma (1984)

(S1) (S2) Family: Cyprinidae

1. Schizothorax richardsonii (Gray) + + +

2. S. plagiostomus (Heckel) + - -

3. S. sinuatus (Heckel) + + +*

4. Schizothoraichthys progastus (McClelland) + - +

5. Tor tor (Hamilton) + +* +

6. T. putitora (Hamilton) + +* +

7. Labeo dero (Hamilton) + +* +

8. Crossocheilus latius (Hamilton) + + -

9. Garra gotyla gotyla (Gray) + + +*

10. G. lamta (Hamilton) + + -

11. Barilius bendelisis (Hamilton) + + +

12. B. vagra (Hamilton) + + +

13. B. barila (Hamilton) + + -

14. B. barna (Hamilton) + + -

Family: Balitoridae

15. N. rupicola (McClelland) + + +

16. N. zonatus (McClelland) + + +

17. N. beavani (Gunther) + + -

18. N. multifasciatus (Day) + + +

Family: Sisoridae

19. Glyptothorax pectinopterus (McClelland) + + -

20. G. madraspatnam (Day) + - -

21. G. cavia (Hamilton) + + -

22. Pseudechenies sulcatus (McClelland) + + -

Family: Schilbidae

23. Clupisoma garua (Hora) + - -

+ Present; - Absent; *: Absent after impoundment (October 29, 2005) Table 6.2. Distribution of fish species along the stretch of Bhagirathi River

S.No. Fish species

Zone A

(Reference Site)

Zone B

(Reservoir)

Zone C

(Impacted Zone)

Zone D

(Downstream/ tailrace zone *)

Family: Cyprinidae

1. Schizothorax richardsonii (Gray) + + + +

2. S. plagiostomus (Heckel) - - - -

3. S. sinuatus (Heckel) + + - +

4. Schizothoraichthys progastus (McClelland) - - + +

5. Tor tor (Hamilton) - - + +

6. T. putitora (Hamilton) - - + +

7. Labeo dero (Hamilton) - - + +

8. Crossocheilus latius (Hamilton) + - - -

9. Garra gotyla gotyla (Gray) + + - +

10. G. lamta (Hamilton) + - - -

11. Barilius bendelisis (Hamilton) + - + +

12. B. vagra (Hamilton) + - + +

13. B. barila (Hamilton) + - - +

14. B. barna (Hamilton) + - - +

Family: Balitoridae

15. N. rupicola (McClelland) + - + +

16. N. zonatus (McClelland) + - + +

17. N. beavani (Gunther) + - - +

18. N. multifasciatus (Day) + - + +

Family: Sisoridae

19. Glyptothorax pectinopterus (McClelland) + + - +

20. G. madraspatnam (Day) - - - -

21. G. cavia (Hamilton) + - - -

22. Pseudechenies sulcatus (McClelland) + - - +

Family: Schilbidae

23. Clupisoma garua (Hora) - - - - *: Bhagirathi zone between Koteshwar and Deoprayag

Table 6.3. Shannon-Wiener diversity index of fish species caught at the reference site (S1) during the first-year of observations (2004-05)

S.No. Fish species Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug 1. Schizothorax sps 0.52 0.46 0.54 0.54 0.54 0.59 0.58 0.51 0.53 0.50 0.52 0.42 2. Schizothoraichthys progastus 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3. Tor sps 0.35 0.21 0.20 0.16 0.13 0.12 0.14 0.19 0.28 0.32 0.20 0.23 4. Labeo dero 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.21 0.23 5. Garra sps 0.35 0.21 0.38 0.39 0.37 0.38 0.39 0.42 0.36 0.32 0.31 0.35 6. Barilius sps 0.45 0.33 0.33 0.33 0.27 0.28 0.39 0.39 0.38 0.42 0.43 0.45 7. Noemacheilus sps 0.21 0.33 0.33 0.33 0.40 0.42 0.39 0.39 0.25 0.28 0.30 0.21 8. Crossocheilus sps 0.37 0.46 0.46 0.52 0.52 0.49 0.39 0.46 0.45 0.42 0.30 0.21 9. Others 0.23 0.21 0.00 0.00 0.00 0.00 0.23 0.19 0.36 0.32 0.31 0.35

Total ( H ) 2.49 2.22 2.24 2.28 2.23 2.27 2.50 2.54 2.61 2.58 2.59 2.46 Table 6.4. Shannon-Wiener diversity index of fish species caught at the impacted site (S2) during the first-year of observations (2004-05)

S.No. Fish species Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug 1. Schizothorax sps 0.35 0.46 0.46 0.46 0.42 0.42 0.47 0.46 0.42 0.49 0.42 0.35 2. Schizothoraichthys progastus 0.00 0.00 0.00 0.00 0.00 0.00 0.39 0.39 0.38 0.42 0.30 0.31 3. Tor sps 0.35 0.31 0.28 0.29 0.27 0.28 0.29 0.32 0.36 0.32 0.31 0.35 4. Labeo dero 0.35 0.32 0.29 0.26 0.28 0.30 0.39 0.37 0.42 0.40 0.31 0.32 5. Garra sps 0.23 0.22 0.31 0.33 0.33 0.35 0.23 0.29 0.26 0.23 0.21 0.25 6. Barilius sps 0.35 0.32 0.40 0.36 0.40 0.39 0.23 0.29 0.18 0.21 0.20 0.23 7. Noemacheilus sps 0.25 0.36 0.36 0.38 0.39 0.32 0.39 0.29 0.38 0.28 0.30 0.29 8. Crossocheilus sps 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9. Others 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total ( H ) 1.88 2.01 2.10 2.08 2.08 2.05 2.38 2.41 2.39 2.35 2.07 2.11

Table 6.5. Shannon-Wiener diversity index of fish species caught at the reference site (S1) during the second-year (2005-06)

S.No. Fish species Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug 1. Schizothorax sps 0.48 0.56 0.54 0.55 0.55 0.58 0.54 0.56 0.55 0.48 0.44 0.42 2. Schizothoraichthys progastus 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3. Tor sps 0.28 0.32 0.29 0.17 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4. Labeo dero 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5. Garra sps 0.42 0.40 0.46 0.40 0.42 0.45 0.41 0.39 0.40 0.35 0.39 0.40 6. Barilius sps 0.28 0.30 0.29 0.36 0.39 0.40 0.33 0.48 0.38 0.33 0.38 0.32 7. Noemacheilus sps 0.28 0.32 0.29 0.39 0.37 0.34 0.25 0.36 0.42 0.43 0.39 0.30 8. Crossocheilus sps 0.28 0.30 0.38 0.33 0.33 0.39 0.33 0.35 0.32 0.35 0.39 0.27 9. Others 0.28 0.00 0.00 0.00 0.00 0.00 0.31 0.33 0.32 0.40 0.32 0.40 Total ( H ) 2.32 2.21 2.25 2.20 2.22 2.16 2.18 2.48 2.39 2.35 2.30 2.12

Table 6.6. Shannon-Wiener diversity index of fish species caught at the impacted site (S2) during the second-year (2005-06)

S.No. Fish species Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug

1. Schizothorax sps 0.22 0.38 0.38 0.36 0.36 0.32 0.33 0.25 0.28 0.22 0.22 0.21 2. Schizothoraichthys progastus 0.00 0.00 0.00 0.00 0.00 0.42 0.46 0.35 0.38 0.33 0.38 0.38 3. Tor sps 0.49 0.38 0.28 0.32 0.29 0.39 0.46 0.48 0.50 0.52 0.50 0.40 4. Labeo dero 0.37 0.30 0.36 0.30 0.32 0.35 0.31 0.39 0.40 0.35 0.39 0.40 5. Garra sps 0.28 0.28 0.29 0.23 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 6. Barilius sps 0.26 0.28 0.22 0.32 0.39 0.32 0.31 0.26 0.30 0.26 0.25 0.23 7. Noemacheilus sps 0.36 0.35 0.30 0.38 0.38 0.33 0.31 0.36 0.28 0.23 0.28 0.28 8. Crossocheilus sps 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9. Others 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total ( H ) 1.98 1.96 1.83 1.92 1.75 2.12 2.20 2.10 2.13 1.92 2.00 1.90

Table 6.7. Concentration of dominance of fish species caught at the reference site (S1) during the first-year of observations (2004-05)

S.No. Fish species Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug 1. Schizothorax sps 0.05 0.09 0.08 0.07 0.08 0.07 0.05 0.05 0.05 0.06 0.07 0.05 2. Schizothoraichthys progastus 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3. Tor sps 0.01 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.00 0.00 4. Labeo dero 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.00 0.00 5. Garra sps 0.01 0.00 0.02 0.02 0.01 0.02 0.01 0.01 0.02 0.01 0.02 0.03 6. Barilius sps 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.00 0.01 0.02 0.02 0.01 7. Noemacheilus sps 0.00 0.01 0.01 0.01 0.01 0.00 0.01 0.01 0.01 0.01 0.00 0.01 8. Crossocheilus sps 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 9. Others 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.02 0.01 0.00 0.00 Total (C) 0.10 0.13 0.12 0.11 0.12 0.11 0.09 0.10 0.10 0.12 0.12 0.11

Table 6.8. Concentration of dominance of fish species caught at the impacted site (S2) during the first-year of observations (2004-05)

S.No. Fish species Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug

1. Schizothorax sps 0.10 0.08 0.07 0.06 0.07 0.04 0.04 0.02 0.01 0.10 0.09 0.05 2. Schizothoraichthys progastus 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.02 0.02 0.03 0.03 0.02 3. Tor sps 0.05 0.04 0.06 0.06 0.02 0.01 0.01 0.01 0.02 0.03 0.06 0.05 4. Labeo dero 0.05 0.04 0.02 0.02 0.02 0.01 0.02 0.02 0.02 0.03 0.03 0.03 5. Garra sps 0.02 0.01 0.02 0.02 0.02 0.03 0.02 0.02 0.01 0.01 0.01 0.01 6. Barilius sps 0.01 0.04 0.02 0.02 0.02 0.03 0.02 0.02 0.02 0.01 0.01 0.02 7. Noemacheilus sps 0.01 0.01 0.02 0.02 0.02 0.01 0.02 0.02 0.02 0.01 0.01 0.02 8. Crossocheilus sps 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9. Others 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total (C) 0.24 0.22 0.20 0.19 0.17 0.13 0.15 0.13 0.12 0.20 0.23 0.20

Table 6.9. Concentration of dominance of fish species caught at the reference site (S1) during the second-year of observations (2005-06)

S.No. Fish species Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug

1. Schizothorax sps 0.08 0.08 0.07 0.08 0.08 0.06 0.07 0.05 0.05 0.06 0.10 0.08 2. Schizothoraichthys progastus 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 3. Tor sps 0.01 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 4. Labeo dero 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5. Garra sps 0.02 0.02 0.04 0.03 0.03 0.05 0.03 0.02 0.03 0.01 0.01 0.02 6. Barilius sps 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.00 0.00 0.01 7. Noemacheilus sps 0.01 0.01 0.00 0.00 0.00 0.00 0.01 0.01 0.01 0.01 0.00 0.01 8. Crossocheilus sps 0.01 0.00 0.01 0.00 0.00 0.01 0.00 0.02 0.01 0.01 0.00 0.01 9. Others 0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.01 0.03 0.01 0.01 0.01 Total (C) 0.13 0.13 0.12 0.12 0.12 0.12 0.12 0.11 0.13 0.11 0.13 0.14

Table 6.10. Concentration of dominance of fish species caught at the impacted site (S2) during the second-year of observations (2005-06)

S.No. Fish species Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug

1. Schizothorax sps 0.04 0.06 0.10 0.12 0.05 0.06 0.03 0.04 0.02 0.03 0.04 0.02 2. Schizothoraichthys progastus 0.00 0.00 0.00 0.00 0.00 0.01 0.07 0.03 0.05 0.04 0.03 0.02 3. Tor sps 0.06 0.05 0.02 0.02 0.08 0.03 0.04 0.03 0.05 0.09 0.07 0.06 4. Labeo dero 0.06 0.05 0.02 0.02 0.04 0.03 0.03 0.06 0.05 0.04 0.03 0.06 5. Garra sps 0.02 0.01 0.02 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 6. Barilius sps 0.02 0.01 0.02 0.02 0.02 0.04 0.01 0.01 0.01 0.01 0.01 0.03 7. Noemacheilus sps 0.02 0.01 0.02 0.04 0.02 0.03 0.01 0.03 0.02 0.01 0.03 0.02 8. Crossocheilus sps 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 9. Others 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Total (C) 0.21 0.20 0.20 0.26 0.22 0.21 0.20 0.19 0.20 0.22 0.22 0.21

Table 6.11. Monthly variations in alpha diversity of fish communities dwelling Bhagirathi recorded at the reference site (S1) and impacted site (S2)

2004-05 Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug

Reference site (S1) 16 16 14 14 16 17 19 18 18 16 16 15

Impacted site (S2) 8 9 9 9 10 10 11 10 10 10 9 8

X 12.0 12.5 11.5 11.5 13.0 13.5 15 14.0 14.0 13.0 12.5 11.5

2005-06

Reference site (S1) 14 13 15 12 13 13 15 16 15 15 14 14

Impacted site (S2) 8 8 7 7 7 6 8 8 9 8 7 7

X 11.0 10.5 11.0 9.5 10.0 9.5 11.5 12.0 12.0 11.5 10.5 10.5

Table 6.12. Beta diversity of fish species of fish communities dwelling Bhagirathi River recorded at the reference site (S1) and impacted site (S2)

2004-06 Total no. of species encountered Average no. of species Beta diversity

Reference site (S1) 19

Impacted site (S2) 12 15.5 1.29

Table 6.13. Statistical t-test and p-value calculated between the fish species at both the sites

S.No. Fish species t-stat value p value

1. Schizothorax sps 7.046 0.003

2. Tor sps 4.138 0.007

3. Labeo dero 5.557 0.003

4. Garra sps 3.388 0.010

5. Barilius sps 3.259 0.016

6. Noemacheilus sps 2.646 0.023

49

Table 6.14. Computation of production of ‘Snow-trout’ recorded at reference site (S1) and impacted site (S2) for the year 2004-05 [N- Number of individuals in 1000 m-2; w - mean wt. of a specimen (g); B - mean biomass (g m-2); G- growth rate and P- production (g m-2 month-1)]

Reference site (S1) Impacted site (S2) Months N w B G P N w B G P

Sep 04 2 160.0 0.320 - - 1 120.0 0.120 - - Oct 04 4 202.0 0.808 0.233 0.188 1 132.0 0.132 0.095 0.013 Nov 04 4 228.0 0.912 0.121 0.110 1 156.0 0.156 0.167 0.026 Dec 04 5 285.0 0.570 0.223 0.127 2 198.0 0.396 0.238 0.094 Jan 05 6 346.0 2.076 0.194 0.403 2 238.0 0.476 0.184 0.088 Feb 05 6 425.0 2.550 0.206 0.524 2 328.0 0.656 0.321 0.210 March 05 5 448.0 2.240 0.053 0.118 3 372.5 1.118 0.127 0.142 April 05 4 452.2 1.809 0.009 0.017 2 398.6 0.797 0.068 0.054 May 05 4 354.0 1.416 -0.245 -0.347 1 268.0 0.268 -0.397 -0.106 June 05 2 280.0 0.560 -0.235 -0.131 1 198.0 0.198 -0.303 -0.060 July 05 1 220.8 0.221 -0.238 -0.052 1 126.9 0.127 -0.445 -0.056 Aug 05 1 180.4 0.180 -0.202 -0.036 1 102.0 0.102 -0.218 -0.022

• P = 0.921 g m-2 yr-1 • P = 0.382 g m-2 yr-1

Table 6.15. Computation of production of ‘Snow-trout’ recorded at impacted site (S2) and impacted site (S2) for the year 2005-06 [N- Number of individuals in 1000 m-2; w - mean wt. of a specimen (g); B - mean biomass (g m-2); G- growth rate and P- production (g m-2 month-1)]

Reference site (S1) Impacted site (S2) Months

N w B G P N w B G P Sep 05 2 226.0 0.452 0.225 0.102 1 90.0 0.090 -0.125 -0.011 Oct 05* 3 250.0 0.750 0.101 0.076 1 120.0 0.12 0.288 0.035 Nov 05 4 278.2 1.113 0.107 0.119 1 176.0 0.176 0.383 0.067 Dec 05 4 294.0 1.176 0.055 0.065 2 214.0 0.428 0.195 0.084 Jan 06 5 352.6 1.763 0.182 0.320 2 292.0 0.584 0.311 0.181 Feb 06 6 428.2 2.569 0.194 0.499 2 388.2 0.776 0.285 0.221 March 06 6 481.5 2.889 0.117 0.339 2 202.0 0.404 -0.653 -0.264 April 06 5 492.0 2.460 0.022 0.053 2 198.5 0.397 -0.017 -0.007 May 06 3 315.4 0.946 -0.445 -0.421 1 126.0 0.126 -0.455 -0.057 June 06 2 210.0 0.420 -0.407 -0.171 1 102.0 0.102 -0.211 -0.022 July 06 2 172.2 0.344 -0.198 -0.068 1 84.0 0.084 -0.194 -0.016 Aug 06 1 156.5 0.157 -0.096 -0.015 1 80.0 0.080 -0.049 -0.004

• P = 0.898 g m-2 yr-1 • P = 0.207 g m-2 yr-1 * Tunnel T-2 was closed in 29th October 2005

50

Table 6.16. Computation of production of ‘Mahseer’ recorded at reference site (S1) and impacted site (S2) for the year 2004-05 [N- Number of individuals in 1000 m-2; w - mean wt. of a specimen (g); B - mean biomass (g m-2); G- growth rate and P- production (g m-2 month-1)]

Reference site (S1) Impacted site (S2)

Months N w B G P N w B G P

Sep 04 1 88.0 0.088 - - 2 80.0 0.160 - - Oct 04 1 64.0 0.064 -0.318 -0.020 1 45.0 0.045 -0.575 -0.026 Nov 04 1 45.0 0.045 -0.352 -0.016 1 32.0 0.032 -0.341 -0.011 Dec 04 1 30.0 0.030 -0.405 -0.012 1 25.0 0.025 -0.247 -0.006 Jan 05 1 44.0 0.044 0.383 0.017 1 30.2 0.030 0.189 0.006 Feb 05 1 52.0 0.052 0.167 0.009 1 34.0 0.034 0.119 0.004 March 05 2 110.0 0.220 0.749 0.165 2 74.0 0.148 0.778 0.115 April 05 2 114.0 0.228 0.036 0.008 2 92.0 0.184 0.218 0.040 May 05 2 126.0 0.252 0.100 0.025 2 112.0 0.224 0.197 0.044 June 05 1 88.0 0.088 -0.359 -0.032 2 78.0 0.156 -0.362 -0.056 July 05 1 74.0 0.074 -0.173 -0.013 2 56.0 0.112 -0.331 -0.037 Aug 05 1 72.0 0.072 -0.027 -0.002 2 45.0 0.090 -0.219 -0.020

• P = 0.129 g m-2 yr-1 • P = 0.053 g m-2 yr-1

Table 6.17. Computation of production of ‘Mahseer’ recorded at impacted site (S2) and impacted site (S2) for the year 2005-06 [N- Number of individuals in 1000 m-2; w - mean wt. of a specimen (g); B - mean biomass (g m-2); G- growth rate and P- production (g m-2 month-1)]

Reference site (S1) Impacted site (S2) Months

N w B G P N w B G P Sep 05 1 92.0 0.092 0.245 0.023 1 40.0 0.040 -0.118 -0.005 Oct 05* 2 112.0 0.224 0.197 0.044 1 33.0 0.033 -0.192 -0.006 Nov 05 1 84.0 0.084 -0.288 -0.024 1 20.0 0.020 -0.501 -0.010 Dec 05 1 60.0 0.060 -0.336 -0.020 1 22.0 0.022 0.095 0.002 Jan 06 1 45.0 0.045 -0.288 -0.013 1 36.0 0.036 0.492 0.018 Feb 06 0 0.0 0.0 0.0 0.0 1 56.0 0.056 0.442 0.025 March 06 0 0.0 0.0 0.0 0.0 2 80.0 0.160 0.357 0.057 April 06 0 0.0 0.0 0.0 0.0 2 86.0 0.172 0.072 0.012 May 06 0 0.0 0.0 0.0 0.0 2 104.5 0.209 0.195 0.041 June 06 0 0.0 0.0 0.0 0.0 2 74.0 0.148 -0.345 -0.051 July 06 0 0.0 0.0 0.0 0.0 2 50.0 0.10 -0.392 -0.039 Aug 06 0 0.0 0.0 0.0 0.0 2 39.0 0.078 -0.248 -0.019

• P = 0.009 g m-2 yr-1 • P = 0.024 g m-2 yr-1 * Tunnel T-2 was closed in 29th October 2005

51

Table 6.18. Multiple regression computed between the production of Snow-trout and the abiotic components at the reference site (S1) during the two-year period

Parameters r r2 Standard error F Intercept t-stat p value

AT -0.694 0.482 0.183 9.317 0.801 3.052 0.012 WT -0.752 0.566 0.168 13.037 1.004 3.611 0.005 WC -0.604 0.365 0.203 5.735 0.438 2.395 0.038 HMD -0.554 0.307 0.212 4.423 0.321 2.103 0.052 Turb -0.433 0.187 0.24 1.248 0.133 3.117 0.011 Tr 0.513 0.263 0.218 3.58 -0.07 2.892 0.088 C -0.020 0.0004 0.254 0.004 0.101 0.062 0.952 TDS -0.502 0.252 0.22 3.368 0.216 2.835 0.096 DO 0.812 0.659 0.149 19.294 -2.574 4.392 0.001 Free CO2 -0.564 0.318 0.21 4.664 0.75 2.16 0.056 pH -0.649 0.421 0.194 7.282 6.82 2.699 0.022 H 0.513 0.263 0.218 3.577 -0.442 1.891 0.088 Al 0.164 0.027 0.251 0.277 -0.3 0.526 0.61 Cl -0.401 0.161 0.233 1.913 0.585 1.383 0.197 N -0.744 0.554 0.17 12.37 0.393 3.517 0.006 P -0.386 0.149 0.235 1.746 0.16 1.321 0.216

Table 6.19. Multiple regression computed between the production of Snow-trout and the

abiotic components at the impacted site (S2) during the two-year period

Parameters r r2 Standard error F Intercept t-stat p value

AT -0.744 0.554 0.062 12.42 0.314 3.524 0.005 WT -0.680 0.462 0.068 8.598 0.271 2.932 0.015 WC -0.699 0.489 0.066 9.551 0.138 3.091 0.011 HMD -0.518 0.268 0.079 3.667 0.105 2.915 0.085 Turb -0.542 0.294 0.087 3.328 0.05 3.152 0.006 Tr 0.340 0.116 0.09 1.612 -0.001 2.783 0.082 C -0.112 0.013 0.092 0.128 0.057 0.357 0.728 TDS -0.413 0.171 0.085 2.053 0.084 1.433 0.058 DO 0.521 0.271 0.093 5.051 0.041 3.068 0.02 Free CO2 -0.579 0.335 0.076 5.067 0.251 2.244 0.049 pH -0.325 0.106 0.088 1.177 0.218 1.085 0.303 H 0.289 0.084 0.089 0.91 -0.068 0.954 0.363 Al -0.068 0.005 0.093 0.047 0.065 0.217 0.833 Cl -0.650 0.423 0.071 7.318 0.275 2.705 0.022 N -0.609 0.371 0.074 5.888 0.128 2.427 0.036 P -0.567 0.321 0.077 4.734 0.082 2.176 0.055

52

Table 6.20. Multiple regression computed between the production of Mahseer and the abiotic components at the reference site (S1) during the two-year period

Parameters r r2 Standard error F Intercept t-stat p value

AT 0.479 0.229 0.046 3.662 0.026 2.249 0.071 WT 0.455 0.207 0.045 3.547 -0.023 2.497 0.063 WC -0.52 0.270 0.039 3.716 0.066 3.928 0.023 HMD -0.364 0.132 0.043 1.532 0.039 2.238 0.044 Turb -0.561 0.315 0.044 2.733 0.018 3.856 0.012 Tr 0.477 0.228 0.046 2.059 0.016 2.243 0.013 C 0.299 0.089 0.044 1.981 -0.025 0.99 0.345 TDS -0.492 0.242 0.044 3.622 0.023 2.788 0.029 DO 0.452 0.204 0.041 2.575 -0.256 3.605 0.034 Free CO2 -0.359 0.129 0.044 2.721 0.066 2.849 0.061 pH -0.116 0.013 0.045 0.137 0.228 0.37 0.719 H 0.124 0.015 0.045 0.156 -0.012 0.395 0.701 Al 0.304 0.092 0.044 1.016 -0.118 1.008 0.337 Cl -0.242 0.059 0.044 0.62 0.065 0.787 0.449 N -0.276 0.076 0.044 0.828 0.032 0.91 0.384 P -0.235 0.055 0.045 0.585 0.019 0.765 0.462

Table 6.21. Multiple regression computed between the production of Mahseer and the

abiotic components at the impacted site (S2) during the two-year period

Parameters r r2 Standard error F Intercept t-stat p value

AT 0.481 0.231 0.062 3.617 0.079 2.786 0.05 WT 0.495 0.245 0.063 3.904 -0.007 2.301 0.07 WC -0.334 0.112 0.06 2.258 0.052 2.122 0.082 HMD -0.427 0.182 0.058 3.225 0.059 2.492 0.087 Turb -0.452 0.204 0.062 3.678 0.026 3.823 0.019 Tr 0.624 0.389 0.05 6.383 -0.039 2.526 0.030 C 0.571 0.326 0.052 4.836 -0.081 2.199 0.053 TDS -0.334 0.112 0.06 2.254 0.046 2.120 0.089 DO 0.415 0.172 0.061 3.098 -0.103 2.048 0.019 Free CO2 -0.338 0.114 0.064 1.114 0.006 2.120 0.071 pH 0.152 0.023 0.063 0.238 -0.045 0.488 0.636 H 0.21 0.044 0.062 0.462 -0.032 0.68 0.512 Al 0.442 0.195 0.057 2.427 -0.140 1.558 0.150 Cl -0.233 0.054 0.062 0.573 0.077 0.757 0.467 N -0.075 0.006 0.064 0.057 0.025 0.239 0.816 P -0.426 0.181 0.058 2.215 0.044 1.488 0.167

53

Table 6.22. Multiple regression computed between the production of Snow-trout and the density of biotic components at the reference site (S1) and the impacted site (S2) during the two-year period (2004-06)

S1 r r2 Standard error F Intercept t-stat p value

Zoobenthos 0.758 0.575 0.159 13.541 -0.224 3.680 0.004

Zooplankton 0.756 0.571 0.160 13.331 -0.177 3.651 0.004

Peri-phyton 0.648 0.420 0.186 7.252 -0.213 2.693 0.023

S2

Zoobenthos 0.572 0.327 0.076 4.859 -0.060 2.204 0.052

Zooplankton 0.705 0.498 0.173 9.908 -0.116 3.148 0.010

Peri-phyton 0.655 0.429 0.184 7.501 -0.238 2.739 0.021 Table 6.23. Multiple regression computed between the production of Mahseer and the

density of biotic components at the reference site (S1) and the impacted site (S2) during the two-year period (2004-06)

S1 r r2 Standard error F Intercept t-stat p value

Zoobenthos 0.169 0.028 0.028 0.292 -0.002 0.541 0.600

Zooplankton 0.109 0.012 0.046 0.121 0.005 0.348 0.735

Peri-phyton 0.372 0.139 0.043 1.610 -0.020 1.269 0.233

S2

Zoobenthos 0.193 0.037 0.063 0.389 0.037 0.624 0.547

Zooplankton 0.629 0.396 0.030 6.553 -0.024 2.560 0.028

Peri-phyton 0.637 0.406 0.030 6.824 -0.046 2.612 0.026

54

Sharma (1988)

6.3%

9.1%2.8%

10.3% 6.6%

57.9%

2.1% 2.5%2.5%

S1 (2004-06)

0.6%14.1%

7.8%

7.8%6.9% 4.7%

0.0%4.0%

54.1%

S2 (2004-06)

19.6%

10.9%

18.8%

17.6%

7.5%

12.3% 0.0%0.0%13.3%

Schizothorax sps Schizothoraichthys progastusTor sps Labeo deroGarra sps Barilius spsNoemacheilus sps Crossocheilus spsOthers

Fig. 6.1. Alterations in fish catch composition of Bhagirathi influenced by Tehri Dam construction over the years (1988-2006)

55

0.9100.970

0.2950.405

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Sharma (1991) Present study (2004-06)

Prod

uctio

n (g

m-2

yr -1

)

S1S2

Fig. 6.2. Depletion in annual production (g m-2 yr-1) of Snow-trout over the years (1991-2006)

0.069

0.161

0.0380.044

-0.05

0.00

0.05

0.10

0.15

0.20

0.25

Sharma (1991) Present study (2004-06)

Prod

uctio

n (g

m-2

yr-1

)

S1S2

Fig. 6.3. Depletion in annual production (g m-2 yr-1) of Mahseer over the years

(1991-2006)

56

Indirect Impacts/ Secondary Effects

§ Habitat Fragmentation § Habitat Isolation § Shrinking of Fish Food

Cumulative and Synergistic Impacts/ Ecological Consequences

§ Impairment of ecosystem function § Ecological stress § Loss of fish diversity

Tehri Dam Construction (cause and effects)

§ Rock stripping and digging of tunnels § Construction of approach roads § Construction of coffer dam and main dam § Dumping of huge muck into Bhagirathi watershed

Direct Impacts/ Primary Effects

§ Geomorphometric transformation of fluvial system § Alteration of composition of bottom substrata § Degradation of water quality § Inundation of feeding, breeding and spawning

grounds of fish § Choking of migration channels of fish

57

Fig. 6.6. Consequences of Tehri Dam construction in terms of direct, indirect and cumulative impacts on coldwater fish resources