Bony herring (Nematalosa erebi) is a freshwater clupeid with a widespread distribution in Australian freshwater ecosystems. Within the Murray-Darling Basin (MDB), its detritivorous and herbivorous diet is thought to facilitate the transfer of energy from basal resources to higher trophic levels. Despite the species’ ecological importance, the drivers of population dynamics remain poorly understood. To investigate the influences of recruitment we analysed 30 years (1994–2025) of biological and catch data (Murray–Darling Basin Fish Surveys, Sustainable Rivers Audit and NSW DPIRD Fisheries surveys) investigating valley and basin scale drivers of young-of-year (YOY) bony herring abundance. Generalised additive models were used to examine relationships between YOY abundance and broad-scale climate variables (Southern Oscillation Index (SOI), Australian Monsoonal Index (AMI) and cumulative MDB rainfall) and valley scale environmental variables (degree days (ºC), cumulative watercourse discharge (m3/s), the longest spell above the 75th percentile flow and maximum water-surface extent (km2) during the reproductive season).
Spatial variation accounted for most of the model deviance with site and valley effects alone explaining 60.2%. Adding climate predictors improved model fit, with SOI and AMI increasing model deviance to 63.6%, however, YOY responses on a basin scale were relatively weak. Cumulative watercourse discharge and degree days were the strongest environmental predictors at the basin scale, yet model deviance only improved to 62%. In contrast, models that allowed environmental variables to vary among valleys received greater model deviance, with the valley-specific cumulative watercourse discharge model explaining 65.5% deviance. Strong positive nonlinear responses to cumulative watercourse discharge were evident in the Barwon–Darling, lower Darling, central Murray and lower Murray, whereas the remaining valleys exhibited weak responses. Overall, our results suggest that there is strong spatial variation in relationships between environmental conditions and bony herring recruitment across the MDB, reflecting the life history flexibility of this highly adaptable species.