River infrastructure and the spread of freshwater invasive species: Inferences from an experimentally-parameterised individual-based model

Invasive species and river infrastructure are major threats to freshwater biodiversity. These stressors are commonly considered in isolation, yet the construction and maintenance of river infrastructure can both enhance and limit the expansion of invasive species. Spatial and temporal limitations of laboratory and field studies, coupled with little consideration of population-level responses (e.g. invasion rate), have limited understanding of the efficacy of infrastructure for long-term, catchment-scale containment of invasive species.This study utilised an individual-based model (IBM) to investigate the ability of a partial riverine barrier to contain the spread of invasive species at large spatio-temporal scales, using American signal crayfish Pacifastacus leniusculus as a model species. The base model (no barrier) accurately recreated longitudinal expansion rates of signal crayfish reported in existing literature. A virtual riverine barrier was added to the base model, with passage at the structure parameterised using existing literature and the results of an experiment that demonstrated no clear relationship between crayfish density and passage efficiency at a Crump weir.Model outputs indicated a weir downstream of the release point had no effect on longitudinal expansion of crayfish, whereas an upstream barrier slowed the invasion rate for 6.5 years after it was first encountered. After the invasion rate had recovered to pre-barrier levels, the invasion front was 2.4 km further downstream than predicted in the absence of a barrier, representing a 1.73 year delay in longitudinal range expansion.Synthesis and applications. Despite substantial negative impacts on native biodiversity, river infrastructure can also delay the spread of freshwater invasive species, representing a trade-off. This demonstrates the need to consider positive ecological consequences of river infrastructure when designing prioritisation techniques for barrier removal and mitigation (e.g. selective fish passage), and suggests that in some cases barriers may provide a useful integrated pest management tool.