The surveys conducted on board FORV Sagar Sampada during 1998-2002 on the Deep Scattering Layer (DSL) revealed a wide spectrum of macrozooplankton in the sonic layers of the oceanic and pelagic realms from surface to 750 m depth. The macrozooplankton biomass was 6.83 and 9.21 g/1000 m3 in the Arabian Sea and 2.14 and 2.61 g/1000 m3 in the Bay of Bengal, respectively, in the day and night hauls. Bathymetric studies showed that the plankton biomass was high at 0-50 m depth. Out of 19 groups of zooplankton from the Arabian Sea, medusae dominated the catch in day (35.6%) and night (31.4%) hauls. Out of 20 groups in the Bay of Bengal, medusae (36.8%) predominated in the day and euphausiids (32.0%) in the night. This paper shows the distribution and abundance of macrozooplankton along the various depths and seasons, including their diurnal vertical migration.

Deep scattering layer, macrozooplankton, biomass, diurnal vertical migration