Nearshore fish community of the Port River-Barker Inlet Estuary, South Australia. I. Effect of thermal effluent on the fish community structure, and distribution and growth of economically important fish species

The nearshore fish community of the Port River-Barker Inlet Estuary was sampled between January 1986 and May 1987 using a beach seine to determine the effect of thermal effluent on the community structure and nursery function of the estuary. A total of 41 species was found in the estuary, with decreasing numbers of species with decreasing distance from the thermal outfall. Cluster analyses and multi-dimensional scaling ordination separated the thermally polluted sites from the non-affected sites. During the summer/auturnn period, thermal effluent only affected water temperature and the species compositions in the inner estuary, and the estuary-opportunistic species Aldrichetta forsteri, Arripis georgiana, A. truttacea and Hyporhamphus melanochir avoided the area at this time. During winter/spring months, thermal effluent acted in the opposite way, with A. forsteri attracted to the warmer waters of the inner estuary. The extended growth season for this species and significantly higher growth rates promoting premature movement out of the inner estuary for S. punctata were additional direct effects. These latter effects may alter the population structures of these species by increasing their vulnerability to heavy localized fishing intensity, aggregation of natural predators and point-source pollution. The species composition of the fish fauna of the estuary may also be indirectly affected by the thermal pollution-mediated seagrass loss in the inner estuary and a method is described to test this hypothesis.