e - poz 2 - Central Institute of Brackishwater Aquaculture

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lake. Kuttyamma (1980) assessed the distribution and abundance of prawns andprawn larvae in Chin backwaters. Raman (1964.1967) made the firstcontribution on the biology of he Macrobrachiurn menbergii and tried toquanttfy its fishery in the lake. He also delineated the nursery grounds of the M.rosenbergri in the river stretches that feed the lake. Rarnan (1975) also gave anaccount of the biology of Ambassis gymnocophalus from the Vembanad lake andcompared with that of the Pulicat lake in Tamil Nadu. Kuttyamma (1980) assessedthe distribution and abundance of pawns and prawn larvae in Cochin backwaters.The fishery estimation during the post barrage phase was mainly by Kurup andSamuel (1980a, 19W, 1983, 1985, 1987). Copinath (1953), Shetty (1965)Kurlan & Sabastian (1982) and Kurup et a/. (1990). Enumeration of the gear andflsh landings was done by them category-wise, sector-wise and species-wise.Kurup and Samuel (1987) listed 150 species of fishes belonging to 100 generacategorlsed under 56 families. The impact of indiscriminate fishery pract~ce andenvironmental stress on t k Macrobrachiurn fishery of the lake has been describedby Kurup (1996). The fishery and biology of four species of Macrobrchium viz.,the M.rosenbergii, M. idella, M.scabriculum, M.equidens In the lake weredescribed by him.The clam fishery has been another important resource of the lake. Its fishery wasstudied by Achary (1987), Kurup et a1 (1990) and Rasalam and Sebastian (1976).The black clam, Villorita cyprinoides formed the major molluscan fishery in theVembanad lake.The survey of the literature reveals that most work on the lake are available for theprebarrage phase and that too restricted to the Cochin sector of the Lake. Theinformation on the southern sector during the post barrage phase is scanty exceptfor the contribution on the fishery by Kurup (1996) and Kurup and Samuel (1980,1987). The ecology stressing on the faunal transformation consequent to thebarrage required more investigation to present a comprehensive change thatoccurred due to the barrage. The Report tries to compensate this lacuna to areasonable extent.
ECOLOGICAL INVESTffiATtONS WRING 1994-97Observations on the water quality parameters indicated a definite pattern ofvariation inflwnced by a combination of saline water intrusion through thebarrage, and the extent of discharge by the four rivers into the lake south of thebarrage CTable-4). The salinity remained the mast important parameter influencingthe general envinmment of the lake. Prior to the construction of the barrage, thetides of a mixed nature were felt during summer upto Pulikkezhu, 80 km south ofCochin connection to the sea, where the maximum tidal range was upto 5 cm, andat the Punnamada, the amplitude was to the extent of 22 cm. Uosanto, 1971).Contrary to this, during the post barrage phase, even in summer, the tidal rangewas restricted till Thaneermukkom Barrage at a distance of only 40 km. Anyenhancement in the salinity further south of the barrage during the summer wasdue to the percolation through the damaged sluices of the barrage. The averagepremonsoon salinity at south of the barrage was 18.47 ppt during the pre-barrgaephase Uosanto, 1971), but reduced to an average of 2.8 ppt during the post-barragephase. Comparatively higher salinity was observed at the western s~de of the lakecaused by the coriolis force operating in the estuary and also due to the absence ofany major freshwater inflow at this bank. The average salin~ty was 0.16 ppt durlngmonsoon and 0.49 ppt during post monsoon season under the present~nvestigation.Temperature was 29.2-32.8 OC ~ndicating a high heat budget for the system. Theshallow nature of the sector (average: depth,1.95 m) coupled with moderate secchidlsc transparency (average:1.26 m) brought almost the entire water column underthe euphotic zone. The average pH of water was near neutral (6.8). During thepre-monsoon stagnation period, the pH was acidic (pH: 6.4; range: 4.5-6.88)part~cularly at stations 2, 4, 7 and 11 (Table 5 & Fig. 3).The d~ssolved oxygen levels were moderate (with a monthly variation rangcng from6.0 to 7.2, average: 6.25 m%L) at all the stations except at Station-1 wheremun~c~pal d~scharge waters brought down the dissolved oxygen to 3.16 mg1Lduring the pre-monsoon period. The Chemical oxygen demand was alsomoderate to h~gh (4.0-28.0 mg/L), again the exceptionally high value recorded atstation-1 during the stagnant pre-monsoon period. The lake in general wascharacterised by low alkalinity (range : 4.0-156.0; average: 22.2 mgfL) except forstatlon 1 and 2.
Page 2 and 3: Ecology and Fisheries Investigation
Page 4: The Vembened take on the south-west
Page 7 and 8: The lakc had already been reclatd c
Page 9 and 10: from the orig~nal marine environmen
Page 11: of this century. The current lwei o
Page 14 and 15: The project was implemented partial
Page 16 and 17: The barrage at Thanneerrnukkom acro
Page 18 and 19: INvISTGATIONS ON THE FISHERY ECOLOG
Page 21: Several literatures are available o
Page 25 and 26: so.
Page 28 and 29: The sediment texture showed that sa
Page 31 and 32: summer. The pure saline forms that
Page 33 and 34: eporxd by Nair et al. (1983) was di
Page 35 and 36: lhJm md tabqodr Onty m spxlcr m6emd
Page 37: A view of the endangered fish speci
Page 41 and 42: Urcrobrachium rosenbergir 57 930 47
Page 43 and 44: The study reveals that the Thanneen
Page 45 and 46: BIBLIOGRAPHY ON VEMBANAD LAKEAnon.
Page 48 and 49: m,T.R. Mii(l. Y. nd Wli, C. M. 1984
Page 50 and 51: Smlathan, P., MccoJuMkr~y, N. I., r
Page 52: I. E-. Mu. bid. E d.I. lndln FWI. A

e - poz 2 - Central Institute of Brackishwater Aquaculture

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