Segregation and feeding of atherinid species (Teleostei) in south-western Australian estuaries

Abstract

Monthly samples were taken throughout the Swan-Avon estuary during 1979 and 1980 to provide information on the partitioning of space and food resources amongst the five most abundant atherinid species found in south-western Australian estuaries. The results demonstrated that Pranesus ogilbyi and Atherinosoma presbyteroides were marine species, which enter the lower estuary in considerable numbers. By contrast, Atherinosoma elongata and Allanetta mugiloides were shown to be estuarine species sensu stricto, which predominatedin the middle estuary. The fifth species, Atherinosoma wallacei, occurred in the upper estuary and more upstream regions of the river. The potential for competition between Atherinosoma species was thus reduced by their occurrence in predominantly different regions of the estuary. When they did occur together, the chance of competition was also apparently further minimized by differences in food preference, with A. elongata ingesting greater amounts of bottom fauna than either A. presbyteroides or A. wallacei. Intergeneric differences in food preferences reduced the potential for competition between A. presbyteroides and P. ogilbyi in the lower estuary and between A. elongata and Allanetta mugiloides in the middle estuary. The records of the Western Australian Museum, and data from extensive surveys, support the view that the succession formed by atherinid species from marine environments through estuaries to inland water follows a similar pattern in all south-western Australian river systems to that described for the Swan-Avon.