Variations in salinity, temperature, dissolved oxygen and zooplankton biomass in the shelf waters off Bombay where the exploratory fishing vessels were operating, studied for one year from April 1972 to April 1973. Hydrographic features in the locality showed double oscillations. Zooplankton biomass exhibited two peaks - one immediately before and the other soon after the southwest monsoon, the latter being secondary in nature. List of dominant zooplankters found in the area in various months are given in the order of their abundance.