'During the IIOE, zooplankton collections were made between 25 degrees N and 45 degrees S latitude and 30 to 120 degrees E longitude. Sampling covered the entire Indian Ocean, with better coverage north of 10 degrees S latitude. Though 1927 samples were collected during IIOE, zooplankton data for 1548 standard hauls were considered to be comparable and these alone were utilized for all publications. A standard haul is defined as an Indian Ocean Standard net collection of zooplankton in the water column under 1 square meter.' (Nair, 2005)
When the depth of the water exceeded 200 meters, the net was hauled from a depth of 200 meters to the surface. In shallower waters, the net was operated from the bottom to the surface. The material studied was collected during both day and night. (Pillai, 1973)
'The samples were then to be preserved in 10% formalin neutralized with hexamethylenetetramine...The samples would then be sent to the Sorting Centre for further processing.' (Hansen, 1966)
References:
Hansen, Vagn Kr., 1966. The Indian Ocean Biological Centre: The centre for sorting plankton samples of the International Indian Ocean Expedition. Deep-Sea Res., 13, pp.229-234.
Nair, V.R., 2005. Database for zooplankton collected during International Indian Ocean Expedition (IIOE) 1960-65. Cooperating project Report. Census of Marine Zooplankton (CMarZ), Connecticut, USA.
Pillai, N. K. 1973. Mysidacea of the Indian Ocean. Handbook to the International Zooplankton Collections, curated and processed at the Indian Ocean Biological Centre 4: 1-125.