Fish productivity: Assessing sustainability in a tropical oxbow lake of Nadia district, West Bengal, India

Abstract

Fish productivity in oxbow lake is impacted severely due to varied unsustainable anthropogenic practices like over exploitation, indiscriminate use of fine meshed fishing gears, jute retting etc. This particular study was conducted in a semi closed oxbow lake ecosystem in eastern India to assess both the present and sustainable fish productivity based on the data collected through direct catch assessment survey, fishing effort survey and catch per unit effort calculation. Hike in relative abundance values like numbers of fish catch (>3.78 times), catch per gear effort (>2.6 times), fish density (>2.65 times) and fall in relative biomass values like catch per gear effort, catch per unit effort and fish standing biomass (>41%) were observed during monsoon compared to premonsoon due to flooded turbid water from the river Ganga and jute retting processes during monsoon. Jute retting and indiscriminate over fishing of the monsoon made fish production reduced by >50% during post monsoon. The current fish productivity was estimated at 1146.64kg/ha/year supporting only 23.33% livelihoods of enlisted fishers and about 97.67% of fish production remains unreported every year in the official records of the cooperative society based on the oxbow lake ecosystem indicating inefficient management. Total sustainable production of 285MT (@5MT/ha/year) with total operating capital need of INR 1.00 crore (@INR 0.01716 crore/ha/year) with benefit cost ratio of 4.28 was estimated as the sustainable and replicable basis for promotion of organic aquaculture supporting 100% livelihoods of all fishers and rejuvenating the management of the present oxbow lake ecosystem.