Spatial relationships and temporal variability in a littoral macrophyte fish assemblage

The presence of macrophytes in lentic systems often exerts a large influence on the spatial and temporal dynamics of the small-bodied fish that inhabit them, particularly in the presence of piscivorous predators. To examine spatial and temporal patterns of fish abundance in macrophyte stands we sampled fish bimonthly with fine-meshed fish traps by day and night in giant rush habitats of a River Murray billabong between October 1995 and September 1996. Three native and three exotic species were found within these habitats during the study, however, catches were dominated by two species of native carp gudgeons (Hypseleotris spp.). Consistently higher numbers of gudgeons were trapped during the day than at night throughout the study period and there was a sustained decline in catch from spring in the first year to the following spring. The results suggest recruitment of juvenile fish spawned during the summer was insufficient for relative abundance to return to the high numbers found at the start of the study. Fine-scale distribution of carp gudgeons within emergent macrophytes was not generally explained by variability in either physical structure or physicochemical variability. This contrasts with many studies of small fish assemblages in macrophytes where piscivorous predators are present.