The major tributaries of the river Ganges basin are currently threatened by various anthropogenic activities which are hampering the ecosystem stability and fish biodiversity of the basin. Multiple indicators were used to prioritize the fish assemblages in the tributaries and to develop an index that is responsive to human-induced environmental changes. A high percentage of invasive species was described with the orgin index at the most disturbed sites of rivers Gomti and Betwa which also represented a substantial amount of biological disturbance. The Fisheries Assessment Integrity Index based on ecological integrity of different segments of the rivers was used to prioritize different sampling sites of the tributaries. Some of the sampling sites in Gomti and Betwa rivers are reflecting disturbed fish assemblages, a very low Fisheries Assessment Integrity Index score, few threatened species, and a high proportion of invasive species. Principal components analysis of the sampling sites, along with fish assemblage, reflected the influence of the habitat parameters on structuring the assemblage pattern. This study identified depth, flow, water quality and land uses in shaping fish assemblages. The combination of various indices in this study should provide more accurate measures in identifying sites of high conservation value.
Over the past several decades, human pressures have unambiguously persuaded global environmental degradation and disruption to a degree that currently requires assessment, intervention, and remediation. In India, in the Ganges basin alone, exploitations such as indiscriminate and illegal fishing, pollution, water abstraction and invasion of invasive species represent some of the problems that affect both ecosystem health and biodiversity (De Silva and Abery, 2007; Sarkar et al., 2012a). The Ganges basin contain a drainage area of about 1,060,000 km2 which is the fifth largest in the world and provide drinking water, food, recreational opportunities and other support services to about 300 million people across three nations viz India, Nepal and Bangladesh (Welcomme, 1985). The tributaries of the river basin also serve as a key source of water for a variety of domestic, agricultural and industrial services and, as a consequence, have suffered changes in water quality and habitat. Despite the urgent need for efficient conservation planning, inadequate effort has been spent on applying systematic conservation planning in these tributaries. In this connection, three large tributaries of the basin viz Ken, Betwa and Gomti were assessed to determine the spatial distribution pattern of fish assemblages with range of indicators on which basis, priority sites where the fish communities and their habitats should be conserved or restored, were identified.
Studies in the major tributaries of the river Ganges viz Gomti, Betwa and Ken revealed the presence of an exceedingly rich species spectrum of fishes with a wide distribution of species, families and genera (Joshi et al., 2009; Sarkar et al., 2010; Lakra et al., 2010; Dubey et al., 2012). But presently, the fish fauna of these rivers are experiencing serious threat on both biodiversity and ecosystem stability and a number of fishes are disappearing due to several anthropogenic factors (Lakra et al., 2010). The few empirical studies of fishes that have occurred in the tributaries in recent years were not understood by or useful for decision makers. The identification of priority areas in the Ganges basin where the conservation efforts should be focused on has traditionally been based on methods which used species richness as a measure of their relative contribution to the native biodiversity (Sarkar et al., 2010; Lakra et al., 2010; Atkore et al., 2011; Dubey et al., 2012). However, all these methods lack specific measures for the assessment of fish community structure and evaluation of conservation value to identify the most suitable areas to focus the conservation efforts. Therefore, the purpose of applying multiple indicators for the prioritization of fish assemblages in the tributaries is to develop an index which can use readily available and measurable fish assemblage attributes that are responsive to human-induced environmental changes.
Biogeography and habitat
The River Gomti is a major tributary of the river Ganges originates from a natural lake in the forested area near Pilibhit town in Uttar Pradesh, about 50 km south of the Himalayan foothills (Figure 1). Lucknow (population about 3.5 million), Sultanpur (population about 0.2 million), and Jaunpur (population about 0.2 million) are the three major urban settlements on the banks of the river. The river receives the untreated domestic waste water from Lucknow city (450,000 m3 day−1) and effluents from industries (distilleries, sugar mills, chemical plants, and others) directly in its course. The variation in land uses and various limiting factors related to ecosystem health of the tributaries are depicted in Table 1.
River Betwa originates in the Raisen district in Madhya Pradesh at an elevation of 475 m above mean sea level and joins river Yamuna near Hamirpur in Uttar Pradesh, traveling a total distance of about 590 km. The river is regulated by 3 large dams (Rajghat, Matatila and Paricha) and 2 small dams/weirs in the middle and upper stretch of the river. The basin is saucer-shaped with sandstone hills around its periphery. The topography and elevation (ranging from 300 to 700 m above masl) cause variation in land use, from flat open wheat and gram growing areas.
The river Ken originates on the northwestern slopes of the Kaimur hills in the Jabalpur district of Madhya Pradesh at an elevation of about 550 masl. The river is the last tributary of Yamuna before its joining with river Ganges. Total length from its origin to the confluence with the river Yamuna is 427 km. River Ken is one of the intact and least polluted rivers in India (http://panna.nic.in) which has been identified as India's first interlinking project (National water development agency (NWDA), 2005). The interlinking projects of the Ken-Betwa link involve building a dam on river Ken and diverting the water to Betwa crossing several rivers/streams. The presence of protected area on the upper stretch and forest cover on the mid-stretch of river Ken tends to have positive impact on its aquatic habitat (Table 1).
An ecosystem-based fisheries assessment approach
Extensive evaluation of the component of the aquatic ecosystem indicators in the Ganges basin along with its tributaries is vital for making decisions about environmental management activities, ecosystem health and measuring progress toward restoration goals. However, it is uncertain how such a task will be implemented. It demands an urgent support of a reliable and common framework of various ecosystem indicators of the basin. These indicators can be used as evidence that reflect the conditions that are being measured. There are also many ways to assess the conservation value of fish assemblages (Darwall and Vié, 2005). The index of biotic integrity (IBI) (Karr and Dudley, 1981) has gained considerable popularity as a method for the assessment of the integrity of fish communities during last 10 to 15 years. It has been criticized by Suter (1993) but with strong counter arguments for the use of the index being presented by Simon and Lyons (1995), Karr and Chu (1997) and Hughes et al. (1998). However, these methods could be modified to reflect regional differences in fish distribution and assemblage structure. In India, the IBI was evaluated based on the fish assemblage structure in the rivers of Central India and tropical Hooghly estuary. Although the ecological principles on which the IBI is based are sound, its application in its original form, as well as adapted versions for use in different regions, present a number of limitations and ecological information that is often not available.
Employing indicators: The current approach
Based on the above-mentioned considerations and the required synoptic nature of the index envisaged for the tributaries of the river Ganges basin, an index adopted from Kleynhans (1999) which was based on fish assemblage integrity of different segments of the river was used to prioritize the fish assemblage at different sampling sites of the tributaries. Maps and past studies of the tributaries were utilized to divide the river into different sites with relatively homogeneous physical habitats.
Fish habitat and distribution
Available distribution records for fish species were collected for the sampling localities and previous studies were also taken into account (Sarkar et al., 2010; Lakra et al., 2010; Joshi et al., 2009; Dubey et al., 2012). This information was grouped according to the identified sampling sites and it provided a description of fish habitat. Sampling was performed covering pre monsoon (March–June), monsoon (July–August) and post monsoon (September and October) seasons. In the present study, habitat characterization and assessment of the importance of the different environmental variables were analyzed with principal components analysis (PCA) using a matrix. Sites belonging to the upper portion of the Gomti (G1 and G2) middle portion of Betwa (B2 and B3) and middle portion of Ken (K3 and K4) were related to stream velocity, depth, turbidity, TDS, substrates, and land use patterns (Figure 2).
Native and non-native species (origin index, OI)
The fish assemblage integrity index (FAII)
Based on the attributes of the fish assemblages native to the river, the FAII aims to measure the biological integrity of the tributaries. The fish assemblage integrity index takes into account three aspects of a fish assemblage:
The components, viz habitat preferences, food preferences, requirement for flowing water and association with habitats with unmodified water quality were taken into account in estimating the intolerance of fish species. Each of these aspects were scored for a species according to low requirement (rating = 1), moderate requirement (rating = 3) and high requirement (rating = 5). The mean of these ratings for a species was calculated to obtain an intolerance score that can lie between 1 (tolerant) and 5 (intolerant). A mean value of about 3 would indicate moderate intolerance.
A total of 12,064 individuals (75 species) were collected from the studied rivers out of which 1284 individuals (six species) were of non native species. For each species expected to be present in a fish habitat segment, the expected frequency of occurrence was estimated for each species from the total number of sampling stretches containing the species and the observed frequency of occurrence calculated:
occurrence at <34% of sites in a segment, score = 1 (infrequent occurrence)
occurrence at 34 to 67% of sites in a segment, score = 3 (frequent occurrence)
occurrence at >67% of sites in a segment, score = 5 (widespread occurrence).
In the present study, a total of four species were considered to be in the category of infrequent occurrence (i.e. score = 1)
The rating of general health and well-being presented problems in the sense that few data exist that can be used to determine expected or reference conditions. Consequently, guidelines used in the application of the IBI were followed. The following procedure was followed to score the health of individual species at a site:
frequency of affected fish >5%, score = 1
frequency of affected fish 2 – 5%, score = 3
frequency of affected fish <2%, score = 5
Calculation of the FAII Score
Exp = Expected for a fish habitat
IT = Intolerance rating for individual species expected to be present in a fish habitat
F = Expected frequency of occurrence rating for individual species expected to be present in a fish habitat
H = Expected health rating for species expected to be present.
Obs = Observed for a fish habitat segment.
The expected conditions for integrity classes are given in Table 2.
Application of indicators: Assessment in the tributaries
Our proposed assessment approach has several advantages. First, it is an integrated, holistic approach using a number of management indicators to get single collective indices for objectives, species, fishery, or ecosystem, unlike other approaches which mostly use individual indicators. Second, the approach is easy to apply. This approach can be applied to any situation even when scientific data are limited. Third, it is possible to evaluate the impact of management practices such as stock re-building programs, habitat recovery programs, or alternative management policies. Fourth, it is possible to compare the status of species, fisheries or ecosystems relative to several management objectives, both spatially and temporally, using the management status index.
Employing these indicators pointed out that the fish assemblages of the tributaries are at the high degree of perturbations at majority of the sampling sites due to regulations by barrages, pollution from sewage discharge and industries etc. The origin index reflected the relatively high percentage of invasive species at the most disturbed sites like G2 and G4 of the Gomti and B5 of the Betwa representing a substantial amount of biological disturbance that may be as much, or more, disruptive of the native fish fauna than the physical and chemical conditions (Figure 3). The natural and anthropogenic threats faced by Gomti and Betwa rivers indicated that the ecological conditions of these two rivers were homogenized as the increasing population of invasive fish like Common Carp, Silver Carp, and Grass Carp could be a great threat to the ecological integrity of the rivers (Sarkar et al., 2012b). Since degraded ecosystems are often more susceptible to successful invasion of invasive fish species, other introduced invasive fishes may also find access and then negatively impact the ecosystem health. Presumably, with sufficient socioeconomic support, the polluted habitat could be improved by waste treatment works and the physical habitat structure by establishing natural riparian wood-lands. In contrast, elimination or reduction of invasive fishes is more problematic because they cannot be controlled by simple technological or engineering techniques, or by modifications in land use.
The assessment of relative FAII score (%) for different sampling sites of the tributaries reflected a significant variation among the sites. Currently the FAII provides an indication of the overall biological integrity in the sites of the rivers. In the Gomti River a general decrease in the relative FAII score was observed in a downstream direction, i.e. sites located in the Lucknow (G2) Haidergarh (G3) Sultanpur (G4) areas. These sites have been associated with overhanging vegetation, water temperature, and TDS, These sites have been impacted by various activities (e.g. water quality, flow regulation, invasion by water hyacinth), intolerant species were, to various degrees still present in these sites. In river Betwa sites located in the downstream i.e Hamirpur (B5) and Orcha (B4) are impacted due to heavy runoff from urban areas and industries. The PCA showed that these sites were associated with river habitat with rowcrop land use, turbidity, sand substrate and depth.
Our assessment also indicates that the tributaries of Ganges basin is relevant because it comprises several attributes associated with ecosystems susceptible to conservation: (a) high species richness with most diverse fish fauna which represents rich diversity of 75 freshwater species of which river Gomti showed a high species richness of 67 species including threatened migratory and economically important species. The cyprinids were the most common family represented with 28 species. Pool Barb (Puntius sophore), Olive Barb (Puntius sarana), Indian River Shad (Gudusia chapra) and large Razor Belly Minnow (Salmostoma bacaila), were ranked as “common” species (i.e. sampled at least once in >75% of the sites in all the studied rivers; (b) the presence of several species in endangered and vulnerable categories. The Tor Barb (Tor tor), Clown Knifefish (Chitala chitala) and Pangas Catfish (Pangasius pangasius) were the most scarce species (occurrence frequency <25%); (c) the limited distribution of some of these species; (d) increased abundance of invasive species; (f) several species of commercial importance.
The information in this study highlights the fact that fish species living in these tributaries are sensitive to anthropogenic disturbance, since instances of local diversity depletion were observed. It is therefore critical, to promote conservation of the river Ganga drainage as a whole, including the formulation of conservation strategies with specific programs geared to protect water quality and the physical habitat, and ensure the preservation of fish fauna diversity in the basin. The PCA of the sampling sites along with the fish assemblage would reflect the influence of the habitat parameters on fish assemblage pattern. The study identified depth, flow, water quality and land uses in shaping fish assemblages. The different conservation indices used in this work showed contrast patterns in the various assemblage types. While each index may be subject to a specific discussion, the combination of various indices is more accurate in identifying sites of high conservation value. Some of the sampling sites in Gomti and Betwa rivers are reflecting disturbed fish assemblages, a very low FAII score, few threatened species, and a high proportion of invasive species. These are considered important for the restoration of fish biodiversity and ecosystem health management.
Although the tributaries have been impacted by various activities (e.g. water quality, flow regulation, invasion by Water Hyacinth, etc.) at all the sites the intolerant fish communities have the potential to recover substantially if favorable conditions occur for long enough and appropriate measures to be designed on those ecosystems. The FAII or any other biological integrity assessment index must not be regarded as providing a final and unequivocal answer as to the biological integrity of a river. Rather it must be seen as part of a system that will lead to more questions being asked in an attempt to solve a particular problem. Nevertheless, as an initial step in this direction in India, these indicators can be used to identify priority areas with less perturbed fish communities of special significance which could be adapted in other contexts or with other tropical rivers to plan appropriate ecosystem management practices. Network based project involving several partners should be planned and implemented in future covering all major river basins for biodiversity conservation and utilization.