In September 1959 the cruise programme for F.R.V. DERWENT HUNTER was changed and cruises were planned to investigate tuna in South-East Australian waters in a much wider area than that covered by the regular coastal operations of F.R.V. MARELDA. The first objective was to determine any associations that might exist between the distributions of souther bluefin tuna (Thunnus maccoyii) and the type of water in which they were caught.

For these investigations a tuna longline was designed and assembled. The details of this are given in the first section of this report. A short summary follows of the length frequency data of the southern bluefin caught on these cruises, and the relations between tuna and water conditions. In the final section the hydrology and tuna longlining results of Cruises DH 11/59 - DH 15/59 and DH 1/60 - DH 4/60 are given.

The zooplankton samples taken during these cruises are not discussed in this report. The results are given in C.S.I.R.O. Aust. (1962) where the regular zooplankton samples taken by F.R.V. MARELDA at selected coastal stations are discussed.