Home Key Lecture
Fish Genetic Resources and Habitat Diversity of the Barak Drainage, Mizoram and Tripura with a Note on Conservation of Endangered Species
Devashish Kar Address
12th Dec 2002
Survey of the fish genetic resources conducted, for the first time, since 2000,, in the river Barak in Assam and its tributaries, viz., Jatinga, Sonai and Dhaleswari; and, in rivers Tuirial and Gomati in Mizoram and Tripura respectively, revealed the occurrence of 103 speices of fishes belonging to 60 genera, 24 families and 10 Orders. Highest species richness was observed in Barak (52) followed by Jatinga (51), Sonai (47), Dhaleswari (33), Tuirial (30) and Gomati (47) with concomitant highest species diversity (Shannon-Wiener) being reflected in Jatinga (H=2.18) followed by Barak (H=1.45), Sonai (H=1.40), Dhaleswari (H= 1.12), Tuirial (H= 1.27) and Gomati (H=1.36). Zoogeographically, these fishes could broadly belong to two broad groups, viz., the primary freshwater group and the peripheral class; while , ecomorphologically, they could be included under four distinct groups. Among the fish assemblage, cyprinids depicted the highest contribution in river Tuirial and lowest in river Barak with their occurrence revealed in pools, pool edges, backwater pools, riffles and riffle edges. Habitat diversity revealed differences in valley segment among the different rivers, some portraying alluvial while others colluvial, the latter being found to portray a diversity of microhabitats to make it colonisable by the rheophilic fishes. Fish cover have been found to be mostly turbulence and depth types, the former the ranging from 2-25 %, while the total cover among all the studied rivers ranged from trace (< 5%) to moderate (5-20 %). Substrate types in the hilly portions of the surveyed rivers were found to be dominated by gravels, cobbles, boulders and bedrocks while in the plain portion of the rivers, the substrate type mostly consists of fines. It is mesoriparian in all the studied rivers but the riparian but the riparian vegetation varies from shrubs to trees in different rivers. Signs of erosion have been observed in all the rivers. Inspite of all our efforts, much of our bewildering diversity of fish resources have come under severe threat, which suggests immediate conservation measures along with concomitant development of fisheries through community participation and involvement of womenfolk. Extent of success in this direction could be revealed through feedbacks from the usergroups regarding their options for management of resources, their developmental aspirations, their modus operandi for resource conservation and so on. Our study revealed a general eagerness among the people for fish conservation. Attempts are being made to declare certain sites in rivers Dhaleswari and Jatinga as `aquatic sanctuaries’ in order to protect critically endangered fishes like Tor progenies.
The Northeast India, comprising of seven provinces, viz., Assam, Arunachal Pradesh, Manipur, Meghalaya, Mizoram and Tripura, is one of the global Hotspots for faunal biodiversity. These provinces with their unique topography, diverse physiographic features and varied watershed patterns are a lucrative field for ichthyological studies with innumerable hill streams, rivers and wetlands. Nevertheless, the region is fed by two major drainage systems. The northern region is drained by the Brahmaputra and its tributaries and the southern region by the Barak and its tributaries. The eastern part, consisting of portions of Manipur, Nagaland and Mizoram, is partly drained by the Chindwin basin.
Much works have been done on the freshwater fishes of India and abroad; but, most of them dealt with either taxonomy or biology (Datta Munshi and Srivastava, 1998; Talwar and Jhingran, 1991; Jayaram, 1981, 1999; Kar, 2000, 2002; Kar et al., 2002 a, b, c, d). Considering the rich ichthyodiversity of this region, first ever survey of 6 principal rivers (viz., River Barak and its tributaries, like Sonai, Jatinga and Dhaleswari in Assam; River Tuirial in Mizoram; and, River Gomati in Tripura), have been done in order to explore the fish species assemblage and their status of management and conservation (Fig. 1).
Habitat parameters were studied after Standard procedures (Armontrout, 1999) and NBFGR Manual (2000). River Continuum Concept (Vannole et al., 1980) was followed in headwater to downstream studies. Studies were also conducted with regard to spatial heterogeneity of river channel across large to spatial scales (Forman and Godran, 1986), and longitudinal and lateral stream margin as well as mid-channel dimensions. Experimental fishing using cast nets (dia 3.7 m), gill nets (vertical height 1.0 m), drag nets (vertical height 2.0 m), triangular scoop nets (vertical height 1.0 m) and a variety of traps were used for fish sampling in different rivers. Also, the technique of camouflaging is used to catch the fishes. Fish identification was done through standard literature (Menon, 1974, 1999; Jayaram, 1981, 1999; Talwar and Jhingran, 1991).
Observation and Discussion
Table 1 depicts the habitat inventory parameters of the studied rivers. It could be noted that there is variation in valley segment having mostly alluvial in the plain regions of Barak valley and Tripura and colluvial in the rheophilic stretches in Mizoram and also in the upstream portions of the rivers in Tripura and Barak valley in Assam. Colluvial valley segment makes a favourable habitat for colonization. Many of the fishes in the rheophilic stretches develop adhesive apparatus in order to negotiate with the fast torrent of water. Further, colluvial valley segment generally provides a diversity of microhabitats in contrast with alluvial valley segment, which exhibits only regime type of reach. A variety of fish covers have been recorded in these rivers, which ranged from depth and turbulence to overhanging vegetation, undercut banks, underwater boulders, deep pools, etc. Turbulence cover ranged from 2-25 % while the total cover among all the studied rivers ranged from trace (< 5 %) to moderate (5-20 %). It is mesoriparian in all the studied rivers and the evergreen trees with some amount of herbs and shrubs constitute the riparian vegetation. Also, the grasses form significant component of riparian vegetation. Agriculture and Tea growing Estates are the principal landuse components in the downstream plain portion of the rivers; while, `jhooming’ is the major type of agriculture in the hilly portion of the rivers involving the catchment. Substrate types in the hilly portion of the surveyed rivers were found to be dominated by gravels, cobbles, boulders and bedrocks; while, in the plain portion of the rivers, the substrate type mostly consists of fines. Signs of erosion have been observed in all the rivers.
103 species of fishes, belonging to 60 genera, 24 families and 10 orders have been recorded on the basis of first ever survey made in the selected six rivers (Table 2). Zoogeographically, these fishes could broadly belong to two broad groups, viz., the Primary freshwater group and the Peripheral group; while, ecomorphologically, they could be included under four distinct groups. Among the fish assemblage, cyprinids depicted the highest contribution in river Tuirial and lowest in river Barak, with their occurrence revealed in pools, pool edges, backwater pools, riffles and riffle edges. Species like Salmostoma bacaila, Amblypharyngodon mola, Puntius conchonius have been recorded in almost all the studied rivers. However, species like Puntius sarana sarana, Ompok bimaculatus and Eutropiichthys vacha could be categorized as vulnerable (Molur and Walker, 1998). Conversely, species like Gudusia chapra, Labeo gonius, and Balitora brucei could be designated as `indeterminate’ (ibid, 1998).
Greater species richness have been found in rivers Barak (52) and Jatinga (51) while lower values have been recorded in rivers Dhaleswari (33) and Tuirial (30). River Jatinga recorded higher speices diversity (Shannon-Wiener) Index (H= 2.18) than the River Tuirial (H= 1.27) while River Dhaleswari depicted the least (H= 1.12) (Table 3).
Several studies have suggested that abiotic parameters like the substrate types, percent pools and channel width integrate with the biotic parameters in order to determine the preferred habitat characteristics of fishes (Newbury and Gaboury, et al., 1993). Features like velocity and temperature of water, substrate type, channel width and percentage of pools have been identified as some of the major parameters in studying life history stages of fish. The present study revealed most of the cyprinid fishes distributed in pools, pool edges, backwater pools and riffles. These fishes do not occur much in the runs and cascades.
Abundance and distribution of fishes is generally controlled by the macro-habitat. The present work reflected riparian cover, substrate type, and habitat volume to be associated with fish density. Habitat volume could be an important attribute in determining species diversity. Low habitat volume reflected low species diversity in rivers Dhaleswari and Tuirial.
Man-made disturbances in the riparian zone have resulted in alteration of natural forests into cultivable land including `jhooming’. Inspite of our efforts, much of our bewildering diversity of fish resources have come under severe threat, which suggests immediate conservation measures along with concomitant development of fisheries through community participation and involvement of womenfolk. Extent of success in this direction could be revealed through feedback’s from the user groups regarding their options for management of resources, their developmental aspirations, their modus operandi for resource conservation and so on. Further, human interventions have major impact in causing depletion of fishes. Natural selection could be productive in the process of evolution because it contributes to continuation of life. However, man-induced extinctions are negative without much contribution to Biodiversity. Nevertheless, our study revealed a general eagerness among the people for fish conservation. Attempts are, thus, being made to declare certain sites in rivers Dhaleswari and Jatinga as `aquatic sanctuaries’ in order to protect critically endangered fishes like Tor species, particularly, Tor progenius.
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Department of Life Science, Assam (Central) University,
Silchar-11, India and
Conservation Forum, Silchar-5, Assam, India