This paper describes the fishery catch structure of Vembanad wetland system during August 2012 to July 2013. The estimates of fishery production indicated an annual landing of 4387.31 t, in which 480.98 t and 3906.33 t contributed by southern and northern zone of Vembanad respectively. Eighty species of finfishes, five species of penaeid shrimps, three species of palaemonid prawns and two species of crabs were identified from the study period. The catch per unit effort (CPUE) value was maximum for gill net (3.04 kg•h −1) followed by stake net (2.43 kg•h −1), Chinese dip net (2.01 kg•h −1), seines (1.2 kg•h −1), cast net (0.72 kg•h −1) and hook and line (0.34 kg•h −1). Biological integrity and fishery production of estuaries in the country are declining mainly due to various man induced activities. Thaneermukkom barrage, the salinity barrier, constructed across the Vembanad wetland system in 1976, transforming the water body into two distinct ecosystems, a fresh water zone on the south and a brackish water zone on the north, resulting in gross changes in physical, chemical and biological entity of the aquatic ecosystem. In the southern zone of Vembanad the marine fish species were less available with the closure of the barrage period. There are signs of decline of the Vembanad fishery resources, evident in the lesser number of species and decline of fishery production. This will lead to biodiversity loss, fish stock reduction and will ultimately affect the livelihood support of the traditional fishers to a large extent, besides affecting other ecological services. A better conservation measure must be implemented for maintaining the sustainable fishery resources in Vembanad.

The objective of the study was to evaluate the survival response of multi-drug resistant enteropathogenic Escherichia coli and Salmonella paratyphi to the salinity fluctuations induced by a saltwater barrier constructed in Vembanadu lake, which separates the lake into a freshwater dominated southern and brackish water dominated northern part. Therefore, microcosms containing freshwater, brackish water and microcosms with different saline concentrations (5, 10, 15, 20, 25 ppt) inoculated with E. coli/S. paratyphi were monitored up to 34 days at 20 and 30 °C. E. coli and S. paratyphi exhibited significantly higher (p < 0.05) survival at 20 °C compared to 30 °C in all microcosms. Despite fresh/brackish water, E. coli and S. paratyphi showed prolonged survival up to 34 days at both temperatures. They also demonstrated better survival potential at all tested saline concentrations except 25 ppt where a significantly higher (p < 0.0001) decay was observed. Therefore, enhanced survival exhibited by the multi-drug resistant enteropathogenic E. coli and S. paratyphi over a wide range of salinity levels suggest that they are able to remain viable for a very long time at higher densities in all seasons of the year in Vembanadu lake irrespective of saline concentrations, and may pose potential public health risks during recreational activities.

Among the zooplankton, Rotifera comprise an integral part of the food chain and are important link between nanoplankton and carnivorous zooplankton. The diversity of rotifers is indicative of the ecological factors of the water body as they respond more quickly to environmental changes and appear as sensitive indicators of changes of water quality. In this context, species diversity of planktonic rotifers and its community assemblage in Vembanad backwater (Ramsar site) has been carried out from March 2012 to February 2013 from ten selected stations on North and South of the Thanneermukkom barrage. Abiotic and biotic parameters were determined and correlated with rotifer abundance to gain information about the forces that assembles the rotifer community in this dynamic environment. Maximum abundance was observed during monsoon (av. 8934 individual . During the present study 26 species of the rotifers belonging to 10 families were observed, with maximum abundance of Brachionus sp. (60%). Predominant species were Brachionus rotundiformis (16.4%), B. calyciflorus (6.6%), B. urceolaris (5.5%), B. plicatilis (4.05%), Keratella tropica (3.2%) and Asplanchna sp. (2.2%). Most of the dominant species observed were eurytopic freshwater forms that became less abundant towards downstream (station 8, 9 and 10) with respect to the salinity gradient prevailing in the estuary. Highest Shannon diversity index (4.51) was observed in station 3 (Rani) and lowest (2.73) in station 10 (Aroor). Multivariate Bio-Env (BEST) analysis showed that temperature, conductivity, salinity and phosphate best determined the abundance and distribution of rotifers in the Vembanad estuary. As the trophic status and rotifer assemblages of an ecosystem are very much related, a comprehensive study on the species diversity and community assemblage of rotifers in Vembanad estuary can furnish a valuable integrative index for further ecological assessment and monitoring of estuarine ecosystems.

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