LANDSCAPE changes such as habitat alterations, fragmentation and loss are causing a decline of many species of flora and fauna at an alarming rate throughout the world1–3. Hence, the emergence of a landscape-based approach for biodiversity assessment and management has assumed significance in recent years as it considers a species as part of a landscape consisting of diverse elements. For instance, deer in a pastureland makes use of several elements, such as heterogeneous vegetation patches in search of variation in fodder, temperature regimes (both warm and cold) and a waterbody for drinking4. The need for integrated management of various landscape elements constituting an ecosystem to maintain its characteristic biodiversity has also been stressed5–7. Various researchers8– 11, highlighted the role of terrestrial ecosystem in the study of freshwater fishes, emphasizing the need to adopt landscape approach, integrating both terrestrial and aquatic ecosystems. Despite the presence of two of the world’s biodiversity hotspots in the vast terrain of India, a landscape approach is yet to gain attention in the conservation or management of the rich biodiversity in general and freshwater fishes in particular.
The Western Ghats, one among the 25 biodiversity hotspots of the world12, is a chain of mountains, stretching north-south along western peninsular India for about 1600 km, harbouring rich flora and fauna. Various forest types such as tropical evergreen, semi-evergreen, moist and dry deciduous and high altitude sholas mingle with natural and man-made grasslands, savannas and scrub, in addition to agriculture, plantation crops, tree monocultures, river-valley projects, mining areas and many other landuses. Over 4000 species of flowering plants (38% endemic), 330 butterflies (11% endemic), 289 fishes (41% endemic), 135 amphibians (75% endemic), 156 reptiles (62% endemic), 508 birds (4% endemic) and 120 mammals (12% endemic)13–16 are among the known biodiversity wealth of the Western Ghats. This rich biodiversity coupled with higher endemism could be attributed to the humid tropical climate, topographical and geological characteristics, and geographical isolation (Arabian Sea to the west and the semiarid Deccan Plateau to the east).
The Western Ghats forms an important watershed for the entire peninsular India, being the source of 37 westflowing rivers and three major east-flowing rivers and their numerous tributaries. The 289 freshwater fish species (41% endemic) reported from the Western Ghats belong to 12 orders, 41 families and 109 genera14,15. Notable among these are 33 species from Aralam Wildlife Sanctuary17, 35 from Periyar River18, 98 from Chalakudy River19, 33 from the Kalakad–Mundanthurai Tiger Reserve20, 92 from Nilgiri Biosphere Reserve21 and 102 from Pune District22. Yadav23 reported 135 species of fish from the part of the Western Ghats covering southern Gujarat, Maharashtra and Karnataka. The four major rivers (Kali, Bedthi, Aghanashini and Sharavathi) in Uttara Kannada District, Karnataka altogether account for 92 fish species24. Arunachalam25 and Bhat24 showed that fish species diversity and abundance are linked to diversity of aquatic habitats. The studies carried out so far, however, lack landscape ecological approach and have practically little information about the nature of terrestrial landscape elements in the watershed.
The present study conducted in the upper catchment area of Sharavathi River in central Western Ghats, India, brings out the diversity of fish species in the selected tributary streams of the river, and their correlation with the predominant vegetation in the catchments of these streams. It also deals with the effects on the fish diversity due to the Linganamakki hydel reservoir. The study indicates that freshwater ecosystems are to be considered as parts of the general landscape (watershed/basin/catchment) and significant modifications in the natural vegetation of their catchments can have detrimental impacts on the native fish fauna.