Geographic Information System-Based Analysis of Fish Diversity Trends of River Meenachil, Southern Western Ghats, Kerala.

In this study, the fish fauna of different geographical zones of Meenachil River was investigated using the spatial interpolation techniques of the Geographical Information System. The variations in fish diversity trends during the pre-monsoon, monsoon, and post-monsoon seasons from 2016 to 2020 along the longitudinal gradient of the Meenachil River were determined using the Kriging interpolation method and semivariograms. Sixty-seven fish species belonging to 15 orders, 29 families, and 46 genera were recorded from the river during the study period. Twenty-five were endemic to the Western Ghats, three were exclusive to Kerala, five were nearly threatened, and three were vulnerable. The midstream of the river recorded maximum diversity indices ranging from (H’) 2.608 to 3.171, reflecting the outcome of local river conservation efforts, and the downstream station with the lowest range (H’) 2.305 -2.643. Cluster analysis showed the spatial similarities in fish diversities between sampling stations. Deterioration in water quality downstream was reflected in the fluctuating levels of TDS (ppm) (21.300±116.828 to 365.000±116.828), Conductivity(µSmcm-1) (42.500±252.372 to 815.000±252.372), Salinity(ppt) (0.100±0.083 to 0.400±0.083) and dissolved oxygen levels(mgL-1) (2.900±0.876 to 5.600±0.876). The study highlights the necessity


Introduction
Gradual changes in fish community composition along the linear gradient of a river from upstream to downstream are better predicted by the longitudinal zonation hypothesis. 1 Tropical and temperate rivers usually exhibit a fairly homogenous river zonation pattern with upstream rithral areas of low species diversity followed by transitional areas with comparatively high diversity and downstream potamal areas with maximum species richness and abundance. 2Reference 3 mentions the anthropogenic impacts on the downstream of rivers and the deviating trends in fish diversity gradients.The Meenachil River of Kerala is the only river of the Western Ghats, having human inhabitancy right from its root source till its mouth, where it confluence to Vembanad Lake. 4 The riverine ecosystem is under multiple stressors, which include catchment disturbances, water diversions, habitat loss and fragmentation, loss of riparian, water pollution, and overfishing exacerbated by climatic fluctuations, which have resulted in substantial shifts in diversity and distribution patterns of many endemic fishes of the region. 5,6ological patterns, changes in community composition, and diversity trends can be examined critically using diversity and similarity indices.Distribution and abundance are the main criteria used to ascertain species' status as "threatened" or "endangered" for the implementation of speciestargeted conservation measures.The conservation strategy should be more effective by integrating the complementary use of the various methodologies and the improved utilization of the available information. 7Despite the fact that GIS is getting extra attention in the fields of hydrology and aquaculture management, their adoption for spatial decision support in this area is still moving extremely slowly. 8he addition of the geographic dimension in the form of GIS provides a better perspective on the diverse data and contributes effectively to global conservation efforts enhancing the conservation of biodiversity by providing integration of information in spatial overlays. 9GIS has been used in conservation biology not just for identifying and mapping a region's biodiversity but also for identifying and prioritizing the conservation areas by examining the habitat features and alterations for the implementation of proper restoration strategies. 10,11n order to triangulate its own position, the GPS recovery system uses at least three satellites and between 24 and 32 microwave-transmitting medium earth orbit satellites. 12To positionize deforestation, river pollution, substratum habitat structure, fish faunal variety, and interpolation, those satellites are currently being used. 8Several researchers have taken biophysical data from satellite photography and incorporated them into simulation models. 13 using the tools for deriving scientific output from the gathered data, GIS and its technologies have added additional flexibility to marine fisheries to produce marine environmental data useful to detect contaminants, keep tabs on fishing activity, map habitats on the sea floor, and quantify the physical and biological characteristics of the water column. 14For the first time in India, a project including the use of GIS in marine fishing is being carried out along the coast of Karnataka state. 15few GIS-based studies have been conducted on the fish distribution and abundance pattern of marine fish species of the Arabian sea, 16 but no such works have been conducted on the riverine fishes of Kerala.17 suggested that the application of RS for studies on the environmental characteristics of the oceans could provide a comprehensive picture on fish distribution, abundance, migration, and other information required for monitoring and managing the ocean ecosystems.The International Symposium on Remote Sensing and Fisheries was hosted in 2010 by the Project "Social Applications in Fisheries and Aquaculture using Remotely Sensed Imagery" (SAFARI) and took place in Kochi, Kerala covered the most recent applications to improve fisheries and aquaculture research, particularly in the creation of possible fishing zones.17 Studies on freshwater ichthyology in Kerala can be traced back to Bloch's work in the late 18th century, followed by [18][19][20][21][22][23][24] made substantial contributions after Francis Day's work to the study of freshwater fishes in Travancore.Despite the several fish diversity studies conducted in the rivers of Kerala, no works have been documented so far on GIS-based zonation and the patterns of fish assemblage in Kerala's rivers.Fish diversity measurements from the Upper Ganges were analysed and mapped utilising spatial interpolation techniques of geographic information systems by. 25 A study was done by 26 using Kriging spatial interpolation methods for the spatial analysis and geographical information system mapping of fish diversity in the Pong reservoir in Himachal Pradesh.From seven locations along the Cauvery River basin in Tamilnadu, India, fish and water samples were collected, examined, and the results were entered into a GIS platform. 8 ivers of the Southern Western Ghats are hotspots of many threatened and endemic species of fishes, which emphasize an urgent need to consider their conservation.27 The fish fauna of the rivers of Southern Western Ghats documented was based on the taxonomy, geographical distribution, and ecological aspects.28 Due to the growing trend of site-specific distinct threats, such information is insufficient to address the essential concerns pertaining to the regional conservation and management of fish biodiversity 29 conducted a geomorphic assessment of the Meenachil river basin using the Geographic Information system. Thre are no thorough going efforts to assess the present conservation status of the fishes of Meenachil River, their distribution, and ecological requirements utilizing the spatial interpolation techniques of geographic information systems, other than a few baseline inventories.
This study uses GIS technology to explore how fish diversity changed along the longitudinal gradient during 2016-2020 along the river and to assess the river's present conservation and fish distribution status.

Study Area
Meenachil River (Fig. 1) with a length of 78 km has a basin area of 1272 km², with a watershed extending from northern latitudes of 9 0 .51' to 9 0 .55'and east longitudes of 76 0 20' to 76.55'. 41The major tributary originates from Annakunnumudi at an elevation of +922m above MSL, confluence to Vembanad lake.

Sampling Methods
Fish samples were collected from seven different sites falling in the up, mid, and downstream of the river (Figs. 2, 3 & 4).Collections were done from January 2016 to December 2020.Fish sampling was executed with the help of fishing experts using different gears based on the physical nature of the habitat.In addition, to cast nets, gill nets, and bag nets, specially designed traps were used to collect fish (Fig. 5, 6 & 7).Species for identification were collected and preserved in 70% ethyl alcohol.Identification was done using standard literature by 43,44 and the conservation status was documented according to IUCN red list 2022 with modifications based on updated literature. 45

Ethical Statement
The least number of fish was used for the study and the remaining ones caught were immediately released into the river without harming them.The study was carried out in accordance with the regulation of the Animal Ethics Institutional Committee.

Water Quality Parameters
Temperature, conductivity, total dissolved solids (TDS mg/L), dissolved oxygen (DO), Salinity (ppt) and pH were evaluated from different sites during different seasons from 2016 to 2020 using a Multiparameter portable meter, HANNA, Model HI 2020-02.

Species Richness and Diversity
Species richness and diversity of the different zones were assessed by Shannon's diversity index, similarities between different zones of the river were compared using by Neighborhood Based Clustering using the software, PAST. 46

GIS Analysis
Study area boundaries were prepared from DEM (Digital elevation model) downloaded from the USGS website. 47The data has a resolution of 30m.DEM was used for the delineation of river basin boundaries and morphometric attributes like drainages and their tributaries.The waterbody (River) in the study area was digitized from the Survey of India Toposheets.The data pertaining to fish were collected from different stretches of the river using GPS and cross-checked with google imagery and toposheet for further verification. 42ll the data layers were cross-checked and processed in WGS 1984 datum.Final data sets were converted and plotted over the ArcGIS Platform for further analysis.After the preliminary data entry process, the dataset was subjected to spatial variation analysis using the Inverse distance weighted (IDW) technique interpolation process. 48DW software forecasts the values that greatly influence more than those with less influence. 49DEM and Vectorised GIS layers were used to prepare the various thematic layers depicting the spatial variation and related aspects in the current study.

Result Fish Species Distribution and Conservation Status
Sixty-seven fish species belonging to 15 orders, 29 families, and 46 genera were recorded from the river during the period.Cypriniformes was the most abundant order having 23 species, and Siluriformes second with 11 species.Cyprinidae was the most dominant family comprising 14 species, followed by Bagridae, comprising six species (Table 2).Twenty-five species were endemic to the Western Ghats (WG), three were exclusive to Kerala (KL), five were categorized as nearly threatened (NT), and three were vulnerable (VU) according to the IUCN criteria.The exotic species reported were distributed in the lower stretch of the river (Fig. 8 & Fig. 9 a, b, c & d).

Fish Diversity Along the Longitudinal Gradient
Fish diversity assessed by Shannon-Weiner Diversity Indices as in Table 3 showed significant seasonal variations in seven different sites along the longitudinal gradient of the river and was depicted through GIS mapping (Fig. 9-11).Neighborhoodbased clustering of sampling sites based on the similarities in their diversity indices is given in Fig. 12-14.(Hamilton,      Among the water quality parameters, total dissolved solids, conductivity, salinity, and dissolved oxygen varied considerably from upstream to downstream stream stretches of the river.Their means showed maximum fluctuations in the downstream Kumarakom station.A more or less uniform temperature and pH were maintained at different sites from 2016-2020 (Fig. 15 a-f).

Discussion
Conservation of riverine fish diversity at the regional level needs spatially mapped information on the current trends of fish diversity and site-specific conservation targets at a relatively accurate scale. 50IS-based research comprised a breakthrough in revealing the trends of riverine fish diversity and prioritizing global conservation. 51In Meenachil River, the lowest fish species heterogeneity was recorded at the Teekoy headwaters, increasing towards Poonjar and Bharananganam down the longitudinal gradient.Diversity increased towards the midstream stations, Mutholy and Cherpunkal, with maximum diversity recorded at the Kattachira site (Table 3 & Fig. 9-11).From the midstream, diversity and abundance were declining towards the estuarine downstream zone of the river at Kumarakom station, where the river confluences to Vembanadu Lake.Contrary to forecasts of higher species richness at the downstream reaches of tropical rivers, the Meenachil River's unexpected species richness and abundance were found in the midstream stretch rather than the downstream estuarine zone. 3he decline in fish diversity and abundance in rivers due to habitat destruction and deterioration in water quality was reported. 52e present study results were consistent with Huet's longitudinal fish zonation concept, 53 emphasizing different river zones along the longitudinal gradient with specific community structures.The headwater system of rivers with low diversity was usually occupied by small-sized nektonic fishes restricted to the region mainly dependent on allochthonous resources, N. triangularis, S.scaturigina, G. mullya, P. fasciata, B. bakeri, and M. guntheri, while the downstream is home to bigger species that are sustained by autochthonous resources. 1,54e midstream geographical zone of Meenachil River was found to be the most diverse region, which maintained consistently high diversity throughout the study period from 2016 to 2020 despite seasonal variations (Table .3 & Fig. 9-11).Species richness generally increased with the area sampled. 55Leaving the headwater tributaries Teekoy and Poonjar, the river gradually widens from Bharananganam and forms the open channel of the midstream zone.The sites Mutholy, Cherpunkal, and Kattachira, falling within the wide-open channel of the river, showed maximum diversity (Table 3), and shared almost similar taxa representations (Fig. 12-14).The order Cypriniformes was 17 in number representing the highest number of taxa (Table .2).Nearly threatened species (NT) Anguilla bengalensis, Anguilla bicolor, Ompok bimaculatus and Wallago attu, vulnerable species (VU) Horabagrus brachysoma, Channa diplogramma and Carinotetraodon travancoricus, data deficient species (DD) Devario aequipinnatus, Puntius mahecola, Anabas testudineus and Ehirava fluviatilis, and the not evaluated species (NE) Pristolepis rubripennis and Piaractus brachypomus were found in the midstream zone (Fig. 8a-d).Species distribution pattern showed more addition than a replacement from the upstream to downstream, 56,57 with a positive relationship between fish size and river width. 1,54,58The highest heterogeneity, maximum abundance, and a maximum number of large-sized fish species were characteristic of the midstream zone of the Meenachil River.The larger species were the W. attu, C. diplogramma, C. marulius, Mastacembelus armatus, A.bengalensis, and Gibelion catla.0][61] The midstream stretch receives several tributaries linked to the major flood plains of the river basin. 62reported the proximity of rivers to flood plains as another significant factor contributing to the higher species richness and diversity of the river's middle reaches than the upper stretches.
"The fish diversity hotspot" Kattachira station of Meenachil River consistently maintained high diversity throughout the study period.The region is ecologically unique, with a 'Reserve Riparian Forest' belt and lateral connectivity to the floodplains of the river.The higher fish diversity and unusual abundance of species were in line with the findings of, 63 describing the riparian zone as one of the most influencing "in-stream diversifier" elements that provide leaves, branches, and wood debris yielding to complex microhabitat patterns, including the riffles, pools, and runs which sustained high species richness.
From the midstream, diversity and abundance were declining towards the downstream estuarine zone of the river, the Kumarakom station, where the river confluences to Vembanadu Lake (Table .3& Fig. 9-11).The wide-open channel of the river splits into distributaries of smaller size in the Kumarakom station before its confluences (Fig. 1).In addition to the true freshwater fishes, the downstream fauna includes secondary species, Brachirus orientalis, Megalops cyprinoides, Scatophagus argus, Ehirava fluviatilis, Gerres setifer, and Sillago sihama which are the anadromous migrants to the estuarine zone of the river from the Arabian Sea.The affected downstream stretch homes five nearly threatened species Anguilla bengalensis, Anguilla bicolor, Brachirus orientalis, Ompok bimaculatus AND Wallago attu, two vulnerable species, Horabagrus brachysoma and Channa diplogramma; four data deficient species Anabas testudineus, Megalops cyprinoides, Ehirava fluviatilis, and Puntius mahecola; and five not evaluated species Hyporhamphus quoyi, Gerres setifer, Silago sihama, Puntius bimaculatus and Piaractus brachypomus (Fig. 8 a-d).
A major ecological problem affecting the downstream of the Meenachil River is the temporary retention of water in the lower stretches due to the closure of the barrage, Thanneermukkam Bund.The barrage was constructed in 1974 across Vembanad Lake and the Arabian Sea to prevent saltwater intrusion into the low-lying paddy fields. 6Closing the bund for six months every year prevents the easy discharge of waters from the rivers before emptying into the Arabian Sea.Organic pollution of the Lake due to the closure of the bund and the drastic decline of the fish populations in Vembanad backwaters and associated water bodies was documented by. 64,5Retention of water in the interconnected distributaries has resulted in the water quality deterioration in the river's lower stretches.This was indicated by the extremely high TDS, conductivity, varying salinity, and very low levels of dissolved oxygen recorded from the Kumarakom station during the present study (Fig. 15 e, f, d & c).In addition, in the past two decades, there has been significant growth in backwater tourism, specifically in the estuarine zone of the river and Vembanadu Lake reported. 65Approximately 187 tons/day of solid waste ultimately reach the Lake from the houseboats, resorts, and hotels without adequate treatment.The downstream fish fauna gets regularly exposed to fluctuating environmental attributes, particularly salinity, conductivity, and TDS, along with the accumulation of high levels of pollutants from various sources.Pollutants from various sources have exacerbated the region's water quality deterioration. 66The riparian belt has also been cleared away for tourism development. 67alysis and Geographic Information Systembased mapping by 25 using the spatial interpolation methods of the many assessments of the Upper Ganges basin's freshwater fish biodiversity showed disparities in spatial overlays which is in agreement with the present study results of varying diversity trends in the different zones of Meenachil River.The upper northern section of the Ganga1 and the mid and lower southern parts of the Alaknanda/ Pindar subbasins were found to have increased species abundance and diversity, according to the composite evaluation of species abundance and index of fish diversity.Contradictory to the above findings, in the present study, the mid-stream zone of the Meenachil River maintained consistently high diversity throughout the study period when compared to the upstream and midstream geographical zones of the river.The abundance of threatened fishes was also found to be fairly distributed among the tributaries of the main waterways of all three subbasins of the Upper Ganges whereas the highest distribution of the threatened species was confined to the lower stretches of the Meenachil River.GISbased fish distribution analysis of Meenachil River reveals the significance of extending the local conservation efforts to the river's most pollutionaffected zones to protect the threatened endemic fish species of the river.

Conclusion
The midstream zone of the Meenachil River supported diversified fish species and a high degree of endemic, nearly threatened, and vulnerable species.The declining native fish diversity from downstream stretches of the Meenachil River has reflected the extent of habitat alterations and pollution due to anthropogenic interventions.Higher diversity recorded at the midstream stretches of the Meenachil River reflected the outcome of local conservation efforts initiated by "Meenachil Nadee Samrakshana Samithi," which was acknowledged by the Government of India as the "Bhaghirath Prayas Samman" on the 'River Day' of 2017. 68Similar efforts should also be extended to the tourism-affected downstream stretches to restore its rich fish faunal diversity.The integration of geographic features with the help of GIS provided a better perspective on the fish diversity data of Meenachil River contributing effectively to regional and global biodiversity conservation efforts.The present study recommends that local conservation efforts should continue along with the bio-banking to check further species loss, adoption of sustainable management policies for riverine habitat and biodiversity conservation, ecosystem functioning and resilience, and the livelihood of humans, to provide a better long-term basis for the conservation of freshwaters and its unique fish resources considering the present global biodiversity crisis.

Fig. 1 :
Fig. 1: Map of Meenachil River showing the sampling sites

Fig. 8 :
Fig. 8: Spatial map showing the IUCN conservation and distribution status of fishes of Meenachil River (a) Nearly Threatened NT; (b) Vulnerable VU; (c) Data deficient DD; (d) Not Evaluated (NE)