Freshwater fish fauna of the Ashambu Hills landscape, southern Western Ghats, India, with notes on some range extensions
Robin Kurian Abraham 1, Nachiket Kelkar 2 & A. Biju Kumar 3
1,2 TC 11/1123, YMR Junction, Kowdiar P.O., Nanthencode, Thiruvananthapuram, Kerala 695003, India
3 Department of Aquatic Biology and Fisheries, University of Kerala, Kariavattom, Thiruvananthapuram, Kerala 695581, India
Email: 1 email@example.com, 2 firstname.lastname@example.org (corresponding author), 3 email@example.com
The Western Ghats mountain range extends along the west coast of India and is crisscrossed with streams, which form the headwaters of several major rivers providing water to the plains of peninsular India. The Ghats represent a globally critical ecosystem and biodiversity hotspot (Myers et al. 2000). Freshwater fish diversity is very high, with around 288 species and a high rate of endemism (>50%) (Daniels 2002; Dahanukar 2004). The southern Western Ghats that comprise the Ashambu (Agasthyamala) Hills landscape in Kerala form a biogeographically unique ecoregion (Nair 1991). As with several other taxa, this region is very rich in fish species diversity and endemism (Bossuyt et al. 2004).
The west flowing rivers south of the Shenkottah/Ariyankavu pass have not been extensively surveyed for fish diversity. Most surveys to date have been conducted either in easily accessible sites or in limited localities along individual rivers. In this paper we provide a systematic, updated checklist of freshwater fishes across five important rivers of Kollam and Thiruvananthapuram districts of Kerala, namely, Kallada, Ithikkara, Vamanapuram, Karamana and Neyyar, based on the available literature, secondary data and field-sampling along these rivers in the Ashambu Hills landscape. Habitat preferences and anthropogenic threats have been listed for each species included in the checklist, along with ecological and threat information. This can facilitate the identification of conservation priorities for freshwater fish diversity in the region.
Materials and Methods
The Kerala part of the Ashambu Hills covers the region southward from the Shenkottah/Ariyankavu Pass with three wildlife sanctuaries (WLS) and two reserve forests (RF) and is contiguous with the Kalakad-Mundanthurai Tiger Reserve (KMTR) to the east, in Tamil Nadu (Fig. 1). The Kallada, Ithikkara, Vamanapuram, Karamana and Neyyar are the main rivers in this landscape, that, with the exception of Ithikkara (origin at 240m), originate at elevations above 1500m from wildlife sanctuaries or semi-protected reserve forests (Basak et al. 1995). These rivers proceed westward to meet the Arabian Sea, passing through a land-use gradient with midland areas dominated by rubber plantations and a lowland matrix of coconut/mixed-garden/paddy cultivation and rural to semi-urban/urban areas. The study was conducted from May 2009 to June 2010.
A preliminary checklist of fish species was prepared based on an exhaustive review of published literature, field guides, ecological studies, short notes and reports, taxonomic assessments and previous checklists from here and neighbouring regions (Silas 1951; Menon 1987; Jayaram 1981, 1991, 2010; Pethiyagoda 1994; Devi et al. 1996, 2005; Tekriwal & Rao 1999; Sheeba 1999; Arunachalam 2000; Biju et al. 2000; Martin et al. 2000; Cherian et al. 2001; Daniels 2002; Bhat 2003, 2004; Easa & Shaji 2003; Dahanukar et al. 2004; Thomas 2004; Raagam & Devi 2004; Pethiyagoda & Kottelat 2005a; Raghavan et al. 2007, 2008; Johnson & Arunachalam 2009; Eschemeyer & Fong 2010). This checklist includes 103 fish species belonging to 53 genera and 24 families (Table 1). Taxonomic treatment is based on Eschmeyer & Fong (2010) and Jayaram (2010).
For primary data collection, 20 sampling locations were selected across the five rivers along the southern Western Ghats (Fig. 1), with uniform coverage of highland, midland and lowland areas. Sampling locations represented four broad land-use types (wildlife sanctuary/reserve forest, rubber plantation, coconut plantation/mixed-garden/paddy, semi-urban/ urban area). Sites at higher elevations and coastal areas were randomly surveyed to record restricted-distribution endemics or occasional estuarine/marine species. The fish surveys and identification were carried out through non-destructive sampling by using sampling methods suited to the nature of river course, stream order, flow, presence of aquatic vegetation and local human disturbance. Visual surveys, cast nets, gill-nets and hooks and lines were used to sample fish species. Species richness data were collected. We also opportunistically collected these data from local fishermen fishing at the same locations. Fish species were identified with the aid of taxonomic keys and field guides (Jayaram 1981, 2010; Easa & Shaji 2003). Information on threats to and ecology of species was also collected based on observation, measurements of stream-related ecological covariates and semi-structured interviews with local key-informants.
A checklist of 103 freshwater fish species for this region was prepared using information from available literature and our sampling. The total number of species sampled by us was 58, belonging to 35 genera and 16 families (Table 1). Of these, 25 species were endemic to the Western Ghats. Four range extensions to southern Kerala were recorded, viz. Garra mcclellandi, Garra hughi, Puntius mahecola and Hypselobarbus jerdoni. Garra mcclellandi was recorded in the Neyyar Wildlife Sanctuary. Garra hughi has been recorded in our study, from the higher elevations (above 900m) of the Shendurney Wildlife Sanctuary, Palode Reserve Forest and the Neyyar Wildlife Sanctuary (Fig. 1, Images 1–4). Hypselobarbus jerdoni is a new record for the Kallada River with in the Shendurney Wildlife Sanctuary and the Kulathupuzha River, a tributary of the Kallada in Kulathupuzha Reserve Forest. This now forms the southernmost record for this species. Puntius mahecola was collected from all five sampled rivers.
Sand-mining was found to be the most significant threat to the fish fauna, followed by dynamite fishing. Important, but rare indigenous food fishes such as Tor malabaricus were particularly threatened by dynamite fishing and the increased presence of exotic species such as Cyprinus carpio and Oreochromis mossambicus introduced in reservoirs and lowland areas. We observed niche overlap between exotic and indigenous species, and in some cases, (e.g. Cyprinus carpio and Tor malabaricus), exclusion of local species by exotic ones.
The present paper provides an updated checklist with the latest taxonomic revisions and range extensions for five river basins of the Ashambu Hills landscape. Studies in this region over the last five decades, from Silas (1951) to Thomas (2004) are restricted in scope, with incomplete coverage of rivers and streams across the elevation gradient of the Agasthyamalai ranges and a focus on particular taxonomic groups. We have made the best use of sporadic prior information on fish fauna in developing this checklist, and hope it will serve as a guide to policy makers, managers and conservationists. The range extensions that we report here underline the need for more intensive surveys across this region.
Garra mcclellandi was recorded earlier from the upper reaches of the Kaveri basin, the Nilgiris and Periyar Lake (Gopi 2000) and the current record of this species from Neyyar is the southward extension of this species. The type locality of G. hughi is the Anamalai Hills, with distribution including the Cardomon and Palani Hills and northern and central rivers of Kerala, and the present report confirms its presence throughout the higher reaches of southern Kerala, up to the southernmost river, Neyyar. However, G. hughi had been recently recorded in the Kallar River of Palode Reserve Forest (Johnson & Arunachalam 2009). According to Jayaram (2010), Hypselobarbus jerdoni is distributed in the Deccan along the Western Ghats down south to the Anamalai Hills, and its southern record was previously from the Chalakkudy River in Kerala (Gopi 2000). The present record confirms its presence further south to the Kallada River in the Ashambu Hills. Pethiyagoda & Kottelat (2005b) considered Puntius mahecola as a valid species and considered P. amphibius as its synonym. These authors re-described the species, with specimens collected from the Kallada River, sampled by us as well. The descriptions of the specimens collected by us were found to be in perfect taxonomic agreement with Pethiyagoda & Kottelat (2005a,b) and we record the presence of this species in all the rivers sampled by us. The earlier reports of P. mahecola from the Western Ghats, which were probably female specimens of P. filamentosus, thus remain to be critically analysed.
We identified sand-mining and dynamite fishing to be the most destructive threats to freshwater fishes of this area. These practices seem to have caused severe habitat destruction and declines of rare substrate-dwelling loach fishes, and many important native food fishes. An example of this is Tor malabaricus, the Malabar Mahseer, which was reported to have been facing extreme population decline across the landscape, mainly attributed to dynamite-fishing. We mostly obtained this species from within protected areas, where dynamite-fishing was absent or negligible. Pollution, dumping of acidic wastes from rubber plantations and introduction of invasive exotic food fishes into dam reservoirs and lowland river areas were the other most critical threats.
This broad-scale survey and sampling provides basic data for occurrence of fish species across the land use gradient in the region, for further targeted sampling to compare these different areas for their contribution to fish conservation, while assessing the magnitude of threats from existing practices (direct and indirect). Our paper thus provides the first step for detailed research on the freshwater fish fauna of the west-flowing rivers of the Ashambu Hills landscape, mainly with regards to taxonomic, ecological and conservation studies.
The conservation approaches suggested in this landscape include strict control over sand mining and unscientific fishing practices such as dynamiting and poisoning, the formation of river sanctuaries outside existing protected areas, construction of fish ladders in dams, in situ and ex situ conservation strategies (with the consideration that fish are also part of Indian wildlife), controlling pollution, and minimizing the threats posed by increasing numbers and diversity of exotic fish species.
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