Further Observations on the Distribution of Striped Tuna, Katsuwonus pelamis L., in Eastern Australian Waters, and its Relation to Surface Temperature

Abstract

The distribution of striped tuna in eastern Australian waters, as indicated by numbers of fish caught per line trolled, was investigated between August 1950 and August 1951. The temperature of the water was recorded every half hour while the vessel was cruising. The data obtained show that the distribution extended from at least as far north as Port Macquarie, New South Wales, to 40 miles south of Tasman Island, Tasmania — much further south than observed in previous years. Occurrence in abundance was seasonal in any specific area off the coast. Movement to the south from the mid north coast of New South Wales began in late spring; movement north from the east Tasmanian coast began in mid autumn. Striped tuna were taken in eastern Australian waters of temperature ranging between 14.7 and 20.8°C., but occurred most plentifully between temperatures of 16.0 and 18.0°C. They had a preference for water of specific temperatures in the areas in which they occur seasonally. Seasonal movement north and south showed a strcng correlation with seasonal changes in water temperatures. Commencement of movement northwards from the south appeared to be influenced by downward change in temperature, which brought about the lower limit of the critical temperature tolerated; this change was coincident with the onset of the seasonal westerly winds. Degree of southerly penetration is related to temperature, whose seasonal fluctuation could explain 'abnormal' years.