Young-of-year fish occupy floodplain pools across life-history strategies despite brief and variable river−floodplain connectivity

Context Floodplain habitats support ecological processes in riverine ecosystems, including fish recruitment. In rivers with brief and variable river−floodplain connectivity, the association of young-of-year fish with floodplain pools is poorly understood. Aims We examined whether young-of-year fish associate with floodplain pools in the Fitzroy River, Western Australia, and whether mesohabitat associations (floodplain v. main channel) aligned with expectations from life-history theory. Methods Fish assemblages were sampled at 60 pools over 4 years. Individuals were classified as young-of-year or older using species-specific size thresholds. Mesohabitat associations were assessed using indicator species analysis applied to detection or non-detection data. Key results Young-of-year from 20 of 21 species were detected in floodplain pools, and 16 species either showed a significant floodplain association or no difference between mesohabitats. Ontogenetic shifts in habitat association were common, with adults of several species primarily associated with main channel pools. Young-of-year mesohabitat associations were not well aligned with life-history theory. Conclusions Floodplain pools are widely occupied by young-of-year fish across life-history strategies, despite brief and variable river−floodplain connectivity. Implications Protecting flows that sustain floodplain pools and reconnect them to the main channel is likely to support fish during early life in this highly variable river system.