DISCUSSION AND CONCLUSION

Fish diversity: A total of 90 fish taxa have been recorded from Aghanashiniof which 59 identified ones are given in the Table no.3. About 22 collected are yet to be identified; as such they are known only from local names and descriptions given by fishermen.The rest, the rarer ones, are to be traced out in the estuaries through subsequent ongoing studies.   Only 43 fish taxa, known by their local names, are known from the Sharavathi estuary, which is impacted by hydro-electric projects. Of these 26 taxa are identified to species level; and efforts are on to trace out the rest, rarer ones, known by local names and descriptions given by fishermen.  As far as the regularly traded species are concerned all have been identified from both the estuaries. (Table 3 and 4).

Table 3: Fish diversity in Aghanashini estuary

Table 4: Fish diversity in Sharavathi estuary

Impact of dams on fisheries: Tropical estuarine areas, free from  major developmental projects are well known for their extremely productive fisheries. All along the Indian west coast the estuarine banks are densely populated with fishing hamlets. Yet practically very little efforts were made hitherto to ascertain how much of income from fisheries is generated estuary-wise, and what happens if the estuary is threatened by industries set up on their banks, or flourishing cities in their vicinities. No study so far also assessed what happens to estuarine fisheries if a hydro-electric project is commissioned in any of the several rivers from Western Ghats.Results of the present investigation shows that  Sharavathi estuary, with two power projects in the upstream areas, at Linganmakki and Gersoppa suffered a serious setback in the fisheries sector with significantly low diversity (only 43 taxa), just about 50% of the total fish taxa from the neighboring Aghanashini, which has about 90 taxa of fishes. The construction of dams are reported to have caused reduction of water depths in the estuaries and loss of spawning and breeding grounds of fishes (Dandekar  2012). Whereas fish migrations upstream in the rivers are affected even by even a single dam (Chicharo et.,al. 2004) multiple dams could obviously worsen this situation as the case study of Sharavathi shows. Decline in fish species and their populations are obviously due to lowering of salinity conditions in the Sharavathi estuary due to almost constant release of huge quantities of fresh water from the upstream dams after power generation. Salinity measurements from six stations in the estuary at different intervals upstream reveal that most of estuary has salinity below 0.5 ppt, indicating fresh water conditions. Lowered salinity is the prime factor in bringing about an ecosystem collapse in Sharavathi, an estuary that was in the past visited by several marine fishes also seasonally for spawning and feeding, according to the local fishermen.  Moreover the dams also act as barriers for downstream transportation of nutrient rich silt from the Western Ghats.Decreases in estuarine salinitycan adversely affectmost estuarine organisms as their distributions are determined primarily by salinity tolerance. In addition to their affects on flow and salinity, dams impact estuarine water quality as well (Weitkamp,L. 1994, Storm,D. 2000).

Estimation of income from fisheries: Annual income from fisheries as well as number of fishing days generated by both Aghanashini and Sharavathi were estimated (Tables 1 and 2).