Spawning dynamics of the eastern gemfish (Rexea solandri) in relation to regional oceanography in south-eastern Australia

Experienced fishers believe the winter aggregations of gemfish are influenc ed by the following: cold bottom currents from the south and east flowing u p onto the shelf; the edge of warm-core eddies; and topographic features al ong the shelf break. These claims were tested through observations made at sea during industry surveys of the winter gemfish seasons 1996-98, and the study of 250 m isotherm charts, sea surface temperature data, and historic catch data. The study generally confirmed the anecdotal information collect ed from the fishers. The first gemfish aggregations of the winter season of ten form on the southern edge of a warm-core eddy. Secondarily, aggregation s tend to form around the northern edge of the warm-core eddy if it is inte racting with the shelf break. Finally, gemfish aggregate around the point a t which the main flow of the East Australian Current (EAC) detaches from th e continental shelf. This timing and location apparently coincides with con ditions conducive to the production of subsurface plumes of nutrient-rich d eep Sub-Antarctic mode Water. These plumes lead to seasonal enhancement of phytoplankton growth along the edge of the continental shelf, which may off er the adaptive advantage of enhancing the survival and growth of larval ge mfish.