Data from: Increased population size of fish in a lowland river following restoration of structural habitat

Most assessments of the effectiveness of river restoration are done at small spatial scales (< 10 km) over short time frames (< 3 yr), potentially failing to capture large-scale mechanisms such as completion of life-history processes, changes to system productivity, or time lags of ecosystem responses. To test the hypothesis that populations of two species of large-bodied, piscivorous native fishes would increase in response to large-scale structural habitat restoration (re-introduction of 4450 coarse woody habitat into a 110-km reach of the Murray River, south-eastern Australia), we collected annual catch, effort, length, and tagging data over seven years for Murray cod (Maccullochella peelii) and golden perch (Macquaria ambigua) in a restored 'intervention' reach and three neighbouring 'control' reaches. We supplemented mark-recapture data with telemetry and angler phone-in data to assess the potentially confounding influences of movement among sampled populations, heterogeneous detection rates, and population vital rates. We applied a Bayesian hierarchical model to estimate changes in population parameters including immigration, emigration, and mortality rates. For Murray cod we observed a three-fold increase in abundance in the population within the intervention reach, while populations declined or fluctuated within the control reaches. Golden perch densities also increased two-fold in the intervention reach. Our results indicate that restoring habitat heterogeneity by adding coarse woody habitats can increase the abundance of fish at a population scale in a large, lowland river. Successful restoration of poor-quality 'sink' habitats for target species relies on connectivity with high-quality 'source' habitats. We recommend that the analysis of restoration success across appropriately large spatial and temporal scales can help identify mechanisms and success rates of other restoration strategies such as restoring fish passage or delivering water for environmental outcomes.