The degraded state of the fragile ecosystem of Chilika lagoon on the east coast of India caused by natural changes and anthropogenic pressure was in the process of restoration through an effective hydrological intervention during 2000 after thorough scientific investigation including EIA study. The rich fisheries of Chilika lagoon that support livelihood of 0.2 million local fisherfolk was in dwindling state during the ecodegradation phase. Studies on fisheries and fish biodiversity of the lagoon for 4 years before and 4 years after the intervention showed the stark and rapid recovery of fishery immediately after opening of the new mouth with sixfold increase in average annual landing. The average productivity (11.3 t km -2 ) and CPUE (6.2 kg boat-day -1 ) during post intervention phase registered 528 and 464% increase, as compared to Pre-intervention years. In total, 277 species of fish and shell fish were documented as occurring in Chilika lagoon before the hydrological intervention. Inventory survey for fish and shell fish species diversity during and after hydrological intervention documented 68 and 97 species, respectively. New records of 56 species of fish and shell fish (7 freshwater, 20 brackishwater and 29 marine) were documented from Chilika lagoon after the hydrological intervention. Analysis of commercial catches showed that the migratory species contributed to the bulk of catches (75% by species and 68% by catch weight). Fish yield and biodiversity seemed to be very sensitive to salinity and hydrologic dynamics of the lagoon. Correlation analysis indicated inverse relationship between water transparency and fish catch (R 2 = 0.715; d.f. = 25; P < 0.01). Positive correlation between salinity and prawn landing (R 2 = 0.542; d.f. = 25; P < 0.01) and salinity and mud crab landing (R 2 = 0.628; d.f. = 25; P < 0.001). Average salinity for the whole lagoon was significantly increased by 42.7% (P < 0.007) as compared to pre-intervention situation. Maintenance of estuarine character of Chilika's ecosystem particularly the salinity gradient, un-hindered auto-recruitment of fish and shell fish and prevention of destructive fishing are the key factors for fisheries enhancement. Unless carefully planned conservation and regulation measures are ensured with the active participation of local communities during the early phase of restoration, the present scenario of fisheries enhancement may not sustain for longer time.

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In this study, a self-organizing map (SOM) was utilized to classify habitats in the Chilika lagoon located in India, the largest lagoon ecosystem in Asia (maximum length, 64.3 km; mean width, 20.1 km). The lagoon was marginally eutrophic (nitrate, 0.25 ± 0.22 mg L -1 ; orthophosphate, 0.26 ± 0.22 mg L -1 ; n = 1,980, respectively) for six years (1999)(2000)(2001)(2002)(2003)(2004), and it used to be warm, shallow, turbid and predominantly brackish. The SOM model successfully identified the changing patterns of limnology in the lagoon using the monthly limnological dataset from 30 study sites (July 1999-December 2004. Comparative re-sectoring evaluation of current monitoring sites was accomplished based on the outcome of the modeling. The new site clustering that emerged from the model was similar to conventional ones, and several sites were reorganized. Water physicochemistry was affected by freshwater inflow during monsoon and the new lagoon mouth constructed in September 2000, which resulted in variations in site characteristics in terms of limnology. The results of this study may provide information on the limnological patterns in Chilika lagoon, and they leave room for further study into functional changes in the lagoon ecology with respect to changes in climatic factor, freshwater flow and lagoon morphology.

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