Preliminary evidence of spawning phenologies of freshwater fish in a wet–dry tropical river: the importance of both wet and dry seasons

Wet–dry tropical rivers are characterised by highly predictable, yet highly variable, seasonal flow regimes. The wet season is often regarded as an important period of ecosystem productivity, dispersal and connectivity, and also for freshwater-fish spawning and recruitment. However, few studies have examined fish spawning across hydrological seasons in these rivers. We conducted a pilot study to determine (1) the temporal occurrence (and hence spawning period), and (2) the suitability of standard sampling methods of young fish in the Daly River, Northern Territory, Australia. Fish spawned throughout the year, with spawning phenologies varying substantially among species. The highest diversity and abundance of young fish occurred during the wet season, although early life stages of a high number of species were also present in the dry-season and transition periods. A high number of species spawned all year round, whereas other species had very discrete spawning periods. Three of the four sampling methods tested were successful in catching early life stages and should be employed in future studies. The present study highlighted that all hydrological seasons in the wet–dry tropics are important for fish spawning, and has important implications for future research on the drivers of spawning patterns, and for predicting the effects of flow modifications on freshwater fishes of the wet–dry tropics.