Effect of hydrological regimes on fish yields in Sri Lankan reservoirs

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.