TROPHICALLY-BASED ASSESSMENT OF THE IMPACTS OF DEEP-WATER SEWAGE DISPOSAL ON A DEMERSAL FISH COMMUNITY

The impacts of sewage disposal on the demersal fish community were ide ntified after approximately 2 years of operation of a deepwater outfal l off Sydney, NSW, Australia. Gut-content analyses were used as a basi s for identifying groups of fish with dietary similarities. Similar re sults from multivariate analyses (Bray-Curtis dissimilarity measure an d MDS) identified 8 trophically-similar groups of fish. The majority o f the fish comprising these groups consumed organisms in the soft-bott om community. Only 5 of the 8 trophic groups identified could be analy sed in detail as individuals comprising the remaining groups were not caught in sufficient numbers near the outfall. Asymmetrical analyses o f variance showed that the numbers of individuals and species in one p articular trophic group increased significantly following the commissi oning of the Bondi deepwater outfall. However, the proportional repres entation of individuals in the 5 trophic groups examined did not chang e. Five hypotheses are advanced to account for the observed impacts. O f these, hypotheses centred around increased habitat complexity and a numerical response to increases in prey abundance warrant further inve stigation. Directions of future research and the limitations of variou s designs to assess environmental impacts are discussed in light of th ese results.