Riverine habitats across the Murray–Darling Basin (MDB) have been substantially modified; particularly they have been impacted by the removal of woody debris and the regulation of flow. Environmental flows are commonly delivered to improve native fish recruitment, however the response to flows is highly variable across space and time, creating challenges for environmental water planning and management. Conceptual models of fish recruitment in rivers propose that successful recruitment depends on interactions between flow and habitat to increase productivity, retain larvae and provide physical structure for predator avoidance. This relationship, however, remains poorly quantified. Additionally, some native species of the MDB operate across river networks beyond the scale of individual reaches, meaning their habitat requirements are likely to be scale dependent.
Using a Basin-wide analysis of juvenile fish abundance, this research investigated how physical and geomorphic habitat complexity interact with flow to explain recruitment across spatial scales. Our findings explore how adult abundance and flow–habitat interactions improve the explanation of fish recruitment variability. By comparing the interactive effects of habitat and flow on fish recruitment, we detail species and catchment specific relationships to habitat, highlighting a lack of uniform response to physical and geomorphic complexity across scales. Finally, we discuss the implications of these results for where and when management actions, such as environmental water delivery and physical habitat restoration, are most likely to maximise native fish recruitment.