Fish diversity studies of two rivers of the northeastern Godavari basin, India
Nilesh K. Heda
SAMVARDHAN (Society for the Conservation of Wetland Resources), Karanja (Lad), Washim, Maharashtra 444105, India
Several ways of measuring the species diversity of biological communities have been described (MacArthur 1965; Whittaker 1970; Pielou 1975; Chao 1984; Magurran 1988, 2004, 2005; Krebs 1989; Chao & Shen 2003), and this diversity is considered by ecologists to be an indicator of community well-being (Magurran 1988). India has considerable ichthyofaunal diversity. Day (1875) described 1,418 species of fish under 342 genera, and a century later Jayaram (1981) listed 742 freshwater species under 233 genera, 64 families and 16 orders from the Indian region. Talwar & Jhingran (1991) estimated 930 species of fresh water fish belonging to 326 genera and 99 families. On a global scale, Indian fish populations represent 11% of species, 24% of genera and 57% of families (NBSAP India 2005). In the central Indian River systems (viz. Narmada, Godavari, Tapti and Krishna) Heda (2009) described 150 species belonging to 26 families. In spite of this rich diversity, literature concerning numerical studies of fish diversity is scarce. Bhat (2003) studied the diversity and ecology of four rivers in the Uttara Kannada District of Karnataka. Kar et al. (2006) studied diversity and the effect of environmental variables on fish of Sone Lake in Assam. The Godavari River, especially its northeastern part, is largely unexplored with regards to species inventory. In this study, an attempt was made to assess and compare the fish diversity of two rivers of the northeastern Godavari basin.
Study area: (Fig. 1)
The Godavari is the second largest river in India after the Ganga, and is often referred as the Vriddh (Old) Ganga or the Dakshin (South) Ganga. It rises near Nasik (Trunbakeshwar) in Maharashtra at an elevation of 1,067m and flows for 1,465km before emptying into the Bay of Bengal.
The first study river, the Kathani, is a tributary of the Wainganga and lies at 20015’.531”N & 80031’.196”E - 20012’.658”N & 79059’.620”E. It is an annual river originating in the Dhanora – Murumgaon hills at an altitude of 426.72m, and it flows west for 70km before emptying into the Wainganga north of Gadchiroli (20010’21”N & 79057’49”E’). It is a mountain torrent river flowing through dry deciduous forest and runs dry in the summer, although water remains in some pools. The overall substratum type of the river is sandy with occasional rocks. The canopy is rich, with the dominant vegetation being bamboo (Dendrocalamus strictus), Ajan (Terminalia sp.) etc. The river flows through a sparsely inhabited area and no dams or significant industrial pollution were noted.
The second study river, the Adan, is a principal tributary of the Painganga and lies at 20012’19.00”N-77010’01”E & 19054’87.6”N-78012’61.4”E. The length of this river is 209.21km. It rises in the Washim District of Maharashtra and meanders north, east and south and meets the Painganga River. The river Arunavati unites with the Adan 13km before it joins the Painganga. The valley of Adan is 10km to 22km wide. The river ceases to flow in summer, though some pools remain in the latter part of its course.
Two dams have been built on the Adan; one at the origin near Sonala village and the other near Karanja (Lad) city. The river flows through scrubland, degraded dry deciduous forest and areas with extensive agriculture (Table 1).
Species richness of both rivers combined: Jackknife 1 measure of species richness showed 56 species, which can be considered an upper bound for the species richness of both rivers combined. Species richness calculated by rarefaction gives 47 species, which is considered the lower bound. Thus I conclude that combining both rivers, number of species ranges from 47 to 56.
Species richness measures calculated for 1508 individuals for river Kathani and 2,386 individuals for Adan. Kathani shows 38 species (Jackknife 1 with SD 2.19) while Adan show 40 (Jackknife 1 with SD 3.32) species. The rarefaction of the two rivers show Adan 34 species and Kathani 32 species at 1501 individuals.
Mann-Whitney U test (Brower et al. 1990) was performed to find out differences in the species richness values. The null hypothesis (H0) put was ‘there is no significant difference between the species richness values of both rivers’. Null hypothesis was rejected as significant difference was detected in both rivers species richness for Jackknife 1 (U = 3413.5, P < 0.0001, CI = 6.77-9.38). However, the rarefied species richness shows no significant difference between the values at similar number of individuals (U = 12685, P = 0.0905, CI = -1.56-0.12). That means at similar number of the individuals both rivers do not show significant differences in the species richness values.
The Shannon index for the Kathani was 2.58, and for the Adan 2.1 (calculated using natural log). The Mann-Whitney U test showed a highly significant difference between rivers (U = 111, P < 0.0001), with the Kathani being more diverse than the Adan. The mean value of the Simpson diversity index for the Adan is 4.8, for the Kathani 8.34 (U = 24, P < 0.0001 with CI = 2.98-3.23) which again confirms that both rivers are differs in their diversity values (Table 3).
Although both rivers are the part of same larger basin, significant differences in diversity values were observed. The Kathani is a small river in comparison to the Adan but shows higher diversity. The difference in the value of the diversity indices and species richness values can be explained by considering anthropogenic factors that include pollution (much less in the Kathani) and damming (the Adan has 2 dams). This study supports earlier studies performed by Dean et al. (1998) on the effect of human induced influences on the diversity of the fish in three small streams in southern Ontario and studies by Habit et al. (2006). Dale et al. (1999) found that an overall decrease in fish abundance occurs with increase in the length of non-forested riparian zones (a situation that can be observed in the Adan) while several studies have demonstrated that dams lower fish species diversity (Michio et al. 2007; Morita & Yamamoto 2002) (Table 4).
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