This record describes the biological datasets obtained on Sprightly Voyage SP 11/79. The data were obtained as part of a time series study of Eddy "J" in the Tasman Sea off the New South Wales Coast in October 1979. At this time the eddy was centred on approximately 34 deg 30 min S and 153 deg 30 min E. Stations inside and outside the eddy were sampled for hydrology/nutrients, phytoplankton fluorescence and particle size, zooplankton (including organic nitrogen), and midwater fishes using the RMT (rectangular midwater trawl) net. Underway data were also collected on surface salinity, night-time light intensity, in vivo fluorescence and particle size, and thermal structure of the water was investigated using XBTs. Within the eddy, the most abundant family of fishes in the midwater trawls was family Myctophidae (lanternfishes). Decapod crustacea, salps and squid were also enumerated. Catch data from the midwater trawls (41 operations) are currently held by the CSIRO Marine and Atmospheric Research Data Centre in Hobart.