Fish assemblage dynamics in an intermittent river of the northern Australian wet–dry tropics

Intermittent rivers make up a large portion of the global river network and are the dominant river type in northern Australia. Increased pressure is being placed on such systems, and a better understanding of their ecology is needed. We examined, over a 7‐year period, the fish fauna of the intermittent Fergusson River, a major tributary of the Daly River of the northern Australia. Changes in habitat structure with the onset of the dry season involved contraction of the riffle/run/pool habitat to a single refugial pool, the size of which was determined by antecedent wet season hydrology. The fishes present comprised a subset of species present within the Daly River main channel and consisted of the most widely distributed of northern Australia's freshwater fishes. The Fergusson River provides suitable spawning habitat for species during the wet season (e.g. Hephaestus fuliginosus, Leiopotherapon unicolor and Neosilurus catfishes) and during the dry season for a different set of species (e.g. Amniataba percoides, Melanotaenia australis and Glossogobius aureus). Little year‐to‐year variation in assemblage structure was observed early in the dry season, whereas interannual variation in late dry season assemblages was substantial. Dry season recruitment imparted some of the interannual variability in assemblage structure recorded between late dry season samples. Piscivorous fishes were an important, but temporally variable, component of the assemblage present in the late dry season refugial habitat, and predation was potentially another important source of variation in assemblage structure.