This dataset contains the Hydrology (HYD) data collected on Southern Surveyor voyage SS 02/91 during legs 1-3. Leg 1 took place off the south and east coasts of Tasmania, around Maatsuker Island and Flinders Island, in June-July 1991; Leg 2 was an orange roughy acoustic survey and took place at St. Helens Hill off the east coast of Tasmania in July-August 1991; and Leg 3 took place in the Tasman Sea off the east coast of Tasmania, in the region approximately 40 miles east of Maria Island during August 1991, as part of a study of hydrological conditions associated with the Japanese longline fishery for southern bluefin tuna. This dataset has been processed and archived within the CSIRO Marine and Atmospheric Research Data Centre in Hobart. Additional information regarding this dataset is contained in the cruise report for this voyage and/or the data processing report. Southern Surveyor on-voyage hydrology data are typically obtained from water samples collected in Niskin bottles at various depths during each CTD cast. Parameters measured normally comprise temperature, salinity, dissolved oxygen, phosphate, nitrate, silicate, and nitrite.