Changes to demersal fish communities in Port Phillip Bay, Australia, over two decades, 1970-91

Abstract

Changes to the structure of fish communities in Port Phillip Bay between 1970 and 1991 were analysed by trawling at 14 stations sampled regularly during 1970-75 and in 1990/91. Differences between stations were compared by using Bray-Curtis dissimilarity indices, multidimensional scaling and analysis of variance for the most abundant species. Differences between two sampling periods in the 1970s appear to be the result of the use of different vessels for trawling. A third vessel was used during 1990/91, but differences in catches between 1972-75 and 1990/91 appear to represent real temporal changes rather than differences between trawl efficiencies. Between 1972-75 and 1990/91, increased fishing pressure is the most likely explanation for declines in several important commercial and recreational species. A consequent decrease in competition may have caused an increase in the abundance of stingarees. A decline in seagrass abundance in the western bay probably reduced the abundance of several seagrass-dependent species. The Japanese goby was introduced into the bay after the mid 1970s, and populations of little rock whiting in the western bay and globefish in deep regions of Port Phillip Bay appear to have increased because of the recent establishment of additional exotic invertebrates.