The modell ing study of flow in Vasishta Godavari estuary

The v as islua branch of the Godavari estuary open s into the Bay of Bengal at Antarvedi,Conditions in the estuary arccharacterized by a seasonally varying fresh water discharge and salt water intrusionfrom the Bay resul tingfrom the flow as~oc ia ted with the se.ni- diu rnal t ide. A numerica l model is applied to simulatethe flow and sali nity structures which have also been documented m the literature. The observations duringmonsoon and post-monsoon seasons arc used in a comparison with the theor etical results which are derived froma model in which turbulenceclosure scheme is used.

Influence of river discharge on zooplankton diet in the Godavari estuary (Bay of Bengal, Indian Ocean)

In estuaries, detrital (i.e., non-living) organic matter (OM) contributes significantly to the particulate organic matter (POM) pool and we hypothesize that it may be a major source of estuarine zooplankton diet. To test this hypothesis, the isotopic composition of carbon (d13C) and nitrogen (d15N) of phytoplankton, zooplankton, and POM was assessed in the Godavari estuary (Bay of Bengal, Indian Ocean) during wet (November) and dry periods (January). As a result of higher riverine discharge, POM concentrations and values of the C/Chl-a ratio during the wet period were higher than those measured during the dry one. Relatively lower δ13CPOM values were observed during wet than dry period and contrasting to that was found for δ15NPOM. Detritus from fresh water algae and C3 plants contributed significantly to the POM pool during the wet and dry period, respectively. Based on isotopic mixing model, detrital OM and phytoplankton mostly characterized the POM pools during the wet and dry periods, respectively. Accordingly, our results suggest also that the zooplankton diet was mostly supported by detrital OM during the wet period and by both phytoplankton and detrital OM during the dry one. The zooplankton trophic level (TL, 2.7) during the wet period was relatively higher than that (1.9) during the dry one, suggesting a relative higher preference for detritus than phytoplankton during the wet period. The results of this study allowed us confirming that detrital OM can significantly support zooplankton production in the Godavari estuary.

BIOLOGICAL STUDIES ON THE ANCHOVY, THRYSSA GAUTAMIENSIS BABU RAO (PISCES: ENGRAULIDAE)

Biology of the anchovy, Thryssa gautamiensis BABU RAO, which forms a fishery in the Godavari estuary (East Coast of India) was studied for the three seasons, i.e. 1959-60, 1960-61 and 196162. The population pattern was studied during the three seasons by means of montly percentage length frequency curves and fitting normal curves. Length weight studies were made for the three seasons, the best fit equations to express the relationship have been calculated and differences of relationships within seasons have been tested. Relative condition ('Kn') variation studies have been made for the different length groups of the fish for the two sexes. The variations of fecundity in relation to length and weight of fish respectively were studied and the equation to express their relationships have been established. The spawning season and the sizes, of ova at different stages of maturity have been determined by means of ova diameter measurement studies. The food preferences of this species have been ascertained by studying the gut contents and their item wise percentage frequencies in different months.