Limnology and status of the fishery of Nelligudda Reservoir (Bangalore: India)

Abstract

Nelligudda Reservoir (area: 80 ha, mean depth: 3.0 m) is a warm dimictic lake
with stable thermal stratification for two extended periods (September-October and
February-May) and with an intermittent period characterised by irregular
circulation. Continuous mixing occurs during June-August. The water is well
buffered, hard (mean alkalinity : 142.7 mg/1), moderately rich in electrolytes (mean
conductivity : 373.4 uS/cm) and low in transparency (mean secchi depth : 51.3 cm).
Clinograde distribution of oxygen, high sestonic carbon (mean : 5.0mg/l) and
chlorophyll 'a' values (mean : 98.5 (ig/1) and high primary production rates (2.4 mg
C/m2/d) suggest that the reservoir is productive . Despite low dissolved nutrient
concentration (soluble reactive phosphorus <10 ug/1), high algal biomass implies
internal cycling of nutrients. The reservoir harbours around 20 autochthonous fish
species of which the exotic Oreochromis mossambicus contributes more than 80%
to the commercial fishery. Growth overfishing has resulted in the decline of mean
landing size of O. mossambicus to around 10cm. The importance of maintaining
a minimum landing size of 20cm is discussed. The catch per unit effort showed
two peaks with a major one in July and a minor one in March.