The effectiveness of anthropogenic in-stream barriers as a management strategy for non-native species

Abstract

Invasive species and river infrastructure are both considered major drivers of freshwater biodiversity loss. However, there is a growing body of research suggesting that the construction, maintenance, or modification of river infrastructure (i.e., exclusion barriers) can limit the spread of invasive species, and thus may be a useful management technique. A quantitative meta-analysis conducted as part of this thesis demonstrated that current research regarding the effects of river infrastructure on the spread of invasive species is limited by ineffective experimental design, small spatio-temporal scales, and minimal consideration of invasion dynamics, meaning further assessment regarding the efficacy of exclusion barriers is essential prior to their widespread implementation.
In this thesis, individual-based modelling was used to address the limitations of previous studies due to its ability to simulate complex invasion dynamics over large spatio-temporal scales, and the American signal crayfish (Pacifastacus leniusculus) was identified as an appropriate model species due to its widespread distribution, rapid rate of secondary range expansion, and overwhelmingly negative ecological and socio-economic impacts.
Additional information regarding the fundamental drivers of signal crayfish dispersal and barrier passage behaviour was required for parameterisation of an individual-based model (IBM), and this was obtained through experimentation and spatial analysis. Flume-based experiments revealed that crayfish population density did not affect barrier passage behaviour, whereas individual personality was an important driver of motivation to pass in-stream structures. Spatial analysis incorporating all signal crayfish records in England demonstrated that invasion rate was affected by boating activity and water temperature, although a number of other abiotic factors (including barrier density) did not affect dispersal.
An initial version of the IBM implemented on a virtual river system demonstrated that a partial barrier could significantly delay the secondary range expansion of signal crayfish, although invasion rates recovered rapidly once the barrier had been passed. The IBM was extended to function on a real river system with multiple barriers, and used to predict the impacts of low-cost barrier modifications on the spread of signal crayfish. These predictions were then integrated with information regarding the overall costs and the impact on native fishes using multi-criteria decision analysis (MCDA). Barrier modifications substantially slowed the spread of signal crayfish, but were costly and negatively impacted habitat availability for native fishes. The combined IBM and MCDA approach effectively identified an optimal combination of modifications in the catchment (involving modifications to a single barrier) that minimised the trade-off between these three competing conservation goals.
The results presented in this thesis demonstrate that exclusion barriers can effectively slow the spread of invasive species over large spatio-temporal scales, suggesting they may perform a useful role in long-term, catchment-scale management plans. The approaches used have enhanced fundamental understanding regarding the influence of in-stream infrastructure on invasion dynamics, and will contribute to the long-term conservation of freshwater biodiversity.

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Identifiers

ORCID for Jack Daniels: orcid.org/0000-0001-8205-0631

ORCID for Suleiman Sharkh: orcid.org/0000-0001-7335-8503

ORCID for Paul Kemp: orcid.org/0000-0003-4470-0589

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