Trophically-based assessment of the impacts of deepwater sewage disposal on a demersal fish community

Impacts on the demersal fish community of sewage disposal from a deepwater outfall off Sydney, NSW, Australia, that had been operating for about two years were studied. Analyses of gut content allowed fish to be grouped according to dietary similarities. The majority consumed organisms in the soft-bottom community. Eight trophically similar groups of fish were identified by means of multivariate analyses, and five of these groups were analyzed in detail. Relative abundance and number of species are graphed, and multivariate analysis results are tabulated. The proportional representation of members of the five closely studied trophic groups was similar before and after the outfall's commissioning, though one group showed a significant increase in the numbers of individuals and species after the outfall was commissioned. The impact of increases in habitat complexity and prey abundance should be investigated further.