Multiscale Investigation of Water Chemistry Effects on Fish Guild Species Richness in Regulated and Nonregulated Rivers of India's Western Ghats: Implications for Restoration

Abstract

Tropical rivers across the world are experiencing rapid degradation and loss of fish species due to flow regulation, pollution, and other anthropogenic pressures. Knowledge of how flow alterations at different scales affect tropical fish diversity remains limited, especially in terms of how resulting changes in water chemistry affect fish communities. We investigated fish guild composition and responses of guild richness to water chemistry in 120 river segments with and without local-scale water removals and pollution. This included two regulated subbasins (with flow regulation by barrages and large-scale water diversions) and two nonregulated subbasins (flows not regulated by these barriers) in India's Western Ghats. Using multivariate ordination and regression models, we identified covariates related to water chemistry and environmental characteristics that explained differences in fish species composition and species richness of three water column position-based fish guilds in the study area. At the subbasin scale, effects of water chemistry were stronger for individual river segments. At the segment scale, no differences in water chemistry were found between segments with and without water removals or pollution in both regulated and nonregulated subbasins. Guild-

Effect of environmental drivers of fish assemblage and diversity patterns in temporal scale in Mongra Reservoir: A case study from one of the tributaries of Mahanadi Basin, Central India

“…Higher inorganic productivity (for which TDS is a proxy) may have supported a greater range of species. Similar findings were noticed in the Western Ghat Rivers (Atkore et al, 2020). The concentrations of nitrate and chlorophyll‐a are strongly negatively correlated with the diversity indices, indicating that they will decline when the reservoir's water level rises and vice versa.…”

Linking flow alteration with fish assemblage structure in a river regulated by a small hydropower project in the Western Ghats of Karnataka, India

“…In the dewatered segment of the dammed river, the dominance of eurytopic species such as D. malabaricus (Table 2) and P. melanympx (Table 3) corresponds with an increase in shallow, pool habitats that support generalists and species adapted to lentic habitats (Carlisle et al, 2010). We also observed that rheophilic species had lower CPUE in the dewatered segment (Table 3) suggesting that dewatering might favour species with opportunistic or intermediate LHSs, an adaption favoured under harsh and unstable physical conditions while filtering out species with periodic LHSs (Atkore et al, 2020;Mims & Olden, 2013;Winemiller, 2005). Furthermore, species such as P. melanympx may be particularly well adapted to dewatered conditions because they are small-bodied, a trait suited to find refuge and evade predation in low-depth habitats (Kubec ˇka et al, 1997).…”

“…In the dewatered and downstream segments of the dammed river, we suspect that flow alteration might be negatively affecting the juvenile size class through lowering of habitat persistence (Freeman et al, 2011;Schlosser, 1985). In addition, fluctuating flows in downstream segment and scouring of sediments might affect the egg survival and reproductive success of lithophilic spawners such as T. khudree (Atkore et al, 2020;Chakrabarty & Homechaudhuri, 2013). Dispersal limitation due to river fragmentation and constraints on recruitment can potentially lead to loss of genetic diversity and increase the possibility of local extinctions of migratory species (Lange et al, 2018;Perkin & Gido, 2012).…”

The Spatial and Temporal Disparity of Fish Assemblage and Its Association with Environmental Factors Through Multivariate Statistical Analysis in Jammu and Kashmir's Himalayan River System.

“…The main driver behind similarity and dissimilarity was seasonality, as it changed hydrological conditions and thus impacted the fish fauna in estuaries. 43,54,55 Species richness showed a correlation with FCO 2 , Ca 2+ and Clin all the sampling stations. 56,57,58,59 The sampling areas with lower elevation had a higher amount of species while the species number decreased as elevation increased supporting Rapoport's rule.…”