The Mighty River Brahmaputra: Aqua Faunal Diversity Preamble Water
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The mighty River Brahmaputra: Aqua faunal diversity Preamble Water and soil are identified as the two essential components which support the vary foundation of any civilization. Water is nature’s such gift which supports immense and diversified life forms ranging from tiny micro organisms to large sized animals. Though the open water of lakes and rivers have received man’s attention for activities like navigation, recreation, water supply and fisheries, their ecological values have often been overlooked. Ward (1989) and Boon (1992) forwarded concept of complex relationship between river systems and the fisheries they sustain and also the important processes in large rivers. Aquatic ecosystems, once considered as a neglected ecosystem throughout the globe though it possess more productivity than the terrestrial systems. Now they have been gaining more attention due to their diverse and tremendous economic as well as aesthetic benefits to mankind. Aquatic ecosystems are critical components of the global environment. In addition to being essential contributors to biodiversity and ecological productivity, they also provide a variety of services for human populations. The interaction of geomorphology and hydrological dynamics of an aquatic system is important for the population dynamics. It is equally important for the habitat quality mainly food availability, current velocity, temperature etc. These factors play a vital role in determining the growth and reproductive success of a population. However, aquatic systems have been increasingly threatened, directly and indirectly, by human activities. In addition to the challenges posed by land-use change, environmental pollution, and water diversion, aquatic systems are expected to soon begin experiencing the added stress of global climate change. It is often said that though the first two world wars were for oil but the third world war might be for the water and countries wealth will be compared with respect to aquatic systems only. The hydrological patterns determine the structure and function of most of the aquatic communities. And high diversity of hydraulic conditions offers highest diversity of fauna (Statzner & Higler, 1986). The water current and the geomorphology of the aquatic systems influence the fish diversity of the system. However the quality of edges (bank of the aquatic body) and bed of the aquatic system are also responsible for diversity of fish fauna (Schiemer et al., 1995). It provides shelter for fish as well as other organisms which may further serve as food for fishes. The hydrological significance of tropical water bodies has often been overlooked by acute needs of human requirements such as progressive industrialization, enhanced food production, domestic use and recreation. The contemporary issues like vulnerability, implementation of new fisheries practices, development of land water interface and growing contamination of the limited water resources have raised concern among present day aquatic life scientists (Menon et al. 2000). India is well-known as land of rivers, has a total 14 major rivers each having catchment area of 20,000 km2 and above. Again it has 44 medium rivers with a catchment area between 2000 and 20,000 km2. It also has 53 small rivers each with 2000 km2 or fewer catchment areas which generally originates from coastal mountains (Nath, 1999). Among the major rivers, three (Brahmaputra, Ganga and the Indus river systems) are international in distribution (CBPCWP, 1982). Nevertheless favourable conditions for fish development are linked to biological and physical factors. Location of spawning sites is influenced by bathymetry, substrate type and diversity of adult fish habitats as well as mechanisms conditioning the primary production of the region. However, physical processes (shelf-slope density front and associated current, continental water inflows, winter mixing and stratification of the water column) influence the final distribution patterns of fish eggs and larvae (Alemany et al., 2006; Sabates et al., 2007). As the recruitment success of species depends on physical processes, the management of fish populations cannot be considered independently of their environment (Parsons & Harrison, 2000), and as such, habitat protection is a vital part of ecosystem-based approaches to fisheries management. Though it is assumed that the natural fish stock has drastically depleted and some of the available fish species are rarely encountered over the years are totally missing but sufficient statistics to establish the same is wanting. The literature available concentrates only on the systematic description of the ichthyofauna, but the information regarding associated issues for better understanding of the problem is almost nil. Estimates of the fish production are highly relevant for understanding ecosystem functioning (Elliott & Hemingway, 2002) and as a precursor to ecosystem (energy budget) modeling. They also allow the predicting of potential yields for fishery species (Cowley & Whitfield, 2002). This is particularly important because of the increased focus on both commercial and recreational fisheries in determining whether the current management regime is adequate to ensure long-term sustainability of the aquatic resources. Further information about impact of hydrobiology, increasing rate of deforestation, erosion along with siltation, extensive use of chemicals in the form of pesticide, herbicide and fertilizer, uncontrolled exercise of fishing gears, living standard of the communities mostly depending on the aquatic resources for living on fishery resources are lacking particularly in this region of the globe. The “sustainability” has been the burning issue for all natural resources. The aquatic resources are also under the same fire. The fishery and aquaculture productions are facing the threat of negative growth with positive growth of population to feed and their adverse activities. The fishery and aquaculture sector is striving hard to become sustainable. Considering the scenario of Indian aquaculture sector only, it is now facing a challenge to find out the direction to bring back industries past growth rate to compete in world aquaculture scenario. Importance of a detailed study of the problems and prospects of the river Brahmaputra cannot be ignored for the development of sustainable management strategies. Long term exploitation and suitable, sustainable protection strategies to the aquatic jewels of this river call for the knowledge of aquatic germplasm along with their diversity and present status. The study is a step to add a little bit knowledge to this field to help the decision makers to take appropriate strategy to overcome the problems. Freshwater biodiversity constitutes a vitally important component of the planet, with a species richness that is relatively higher compared to both terrestrial and marine ecosystems (Gleick, 1996). South and Southeast Asia is one of the most speciose areas on the planet containing 20% of all known freshwater vertebrate species and 25% of known aquatic plants (Balian et al, 2008). The Eastern Himalaya region is part of two larger biodiversity hotspots: the Indo-Burma and the Himalaya Hotspots. The high biodiversity of the region is attributed to the recent geological history (the collision of Indian, Chinese and Burmese plates) and the Himalayan orogeny which played an important role in the speciation and evolution of groups inhabiting mountain streams (Kottelat, 1989) The Brahmaputra- Topography, geology and climate The Brahmaputra river system draining from the north slopes of the Central and Eastern Himalaya is one of the very braided rivers of the world, which flows through China (Tibet), India (Arunachal Pradesh and Assam) and Bangladesh (Rao, 1979). The Brahmaputra river system lies between the latitude 230N and 320N and longitude 800E and 97030∕ E. It is the largest river system of Indian sub-continent and comprises 5,80,000 km2 up to its confluence with the Ganga at Gualundo in Bangladesh and thus forms a major part of the Ganga-Brahmaputra-Meghna basin (Phukan, 2006). With the voluminous discharge at the mouth with the flow of 19,830 m3 sec-1 Brahmaputra ranks fourth in the world in terms of average discharge (Goswami, 1985). The Tsangpo river of China, flows through the state of Arunachal, India for 278 km, where it is called Dihang or Siang, The Dihang meets its principal tributaries, the Lohit and the Dibang almost together in the Eastern part of Assam near Kobo in the west of Saikhowa ghat, Assam and from this trijunction the river is known as the Brahmaputra. The Braided River Brahmaputra flows for 640 km through the state of Assam entirely through an alluvial valley. Brahmaputra is not only regarded as a river, it becomes the lifeline for the people residing in its bank. It receives 47 tributaries on its both southern and northern banks. The rier system is the principal water source of Assam and obviously, the principal source of capture fisheries in the state. Needless to say that, the river system is rich in diversity of aqua fauna. Despite of the importance of the river system, there is practically no information about the fauna of Brahmaputra, except fishes of some areas that too not in detail. The Brahmaputra valley is narrow, the average width is only about 80km from foothill to foothill and the river itself occupies 6-9km. The river is considerably fast in Tibet and Arunachal Pradesh, but between Kobo and Dibrugarh the gradient of river is reduced. After Dibrugarh