NEARSHORE FISH COMMUNITY OF THE PORT RIVER BARKER INLET ESTUARY, SOUTH AUSTRALIA .1. 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 wa s sampled between January 1986 and May 1987 using a beach seine to det ermine the effect of thermal effluent on the community structure and n ursery 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 scali ng ordination separated the thermally polluted sites from the non-affe cted sites. During the summer/autumn period, thermal effluent only aff ected water temperature and the species compositions in the inner estu ary, and the estuary-opportunistic species Aldrichetta forsteri, Arrip is georgiana, A. truttacea and Hyporhamphus melanochir avoided the are a 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 sig nificantly higher growth rates promoting premature movement out of the inner estuary for S. punctata were additional direct effects. These l atter effects may alter the population structures of these species by increasing their vulnerability to heavy localized fishing intensity, a ggregation of natural predators and point-source pollution. The specie s 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.