Effect of hydrological regimes on fish yields in Sri Lankan reservoirs
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Date
2001
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Reservoir and Culture-based Fisheries: Biology and Management
Abstract
The need for empirical models for predicting fish yields in lakes and reservoirs, both in tropical
and temperate regions, has long been recognised because investigation of the fisheries of individual
water bodies for management purposes is prohibitive. In a previous study, morphological and
edaphic factors, including extents of catchment areas in reservoirs of Sri Lanka, were found to
influence fish yields. Hydraulic retention time is reported to be another factor influencing fish
yields in tropical reservoirs. This paper attempts to investigate the effect of hydrological regimes
on fish yields in irrigation reservoirs of Sri Lanka. Daily catch and effort data were collected from
10 shallow irrigation reservoirs from December 1997 to September 1999. Nitrate, phosphate and
chlorophyll-a content in each reservoir were determined once in two months. Hypsographic curves
(i.e. area-water depth relationships) and monthly mean data on reservoir capacity, water level,
reservoir area and total outflow volume were obtained from the Department of Irrigation. Flushing
rate (outflow/reservoir capacity) had little influence on water nutrients, chlorophyll-a and fish
yields in reservoirs. As irrigation authorities control the hydrological regimes of these reservoirs,
strong co-ordination between fisheries and irrigation authorities is useful for augmenting fish yields
in the reservoirs of Sri Lanka.