A toolkit for optimizing fish passage barrier mitigation actions

Abstract

Summary1. The presence of dams, stream-road crossings, and other infrastructure often compromises the connectivity of rivers, leading to reduced sh abundance and diversity. The assessment and mitigation of river barriers is critical to the success of restoration eorts aimed at restoring river integrity.2. In this paper, we present a combined modeling approach involving statistical regression methods and mixed integer linear programming to maximize resident sh species richness within a catchment through targeted barrier mitigation. Compared to existing approaches, our proposed method provides enhanced biological realism while avoiding the use of complex and computationally intensive population/ecosystem models.3. To estimate barrier passability quickly and at low cost, we further outline a rapid barrier assessment methodology. The methodology is used to characterize potential passage barriers for various sh species common to the UK but can be readily adapted to dierent planning areas and other species of interest. 4. We demonstrate the applicability of our barrier assessment and prioritization approach based on a case study of the River Wey, located in south-east England. We nd that signicant increases in species richness can be achieved for modest investment in barrier mitigation. In particular, dams and weirs with low passability located on mid to high order streams are identied as top priorities for mitigation.5. Synthesis and applications. Our study shows the benets of combining a coarse resolution barrier assessment methodology with state-of-the art optimization modeling to cost-eectively plan sh passage barrier mitigation actions. The modeling approach can help inform on-the-ground river restoration decision making by providing a recommended course of action that best allocates limited resources in order to restore longitudinal connectivity and maximize ecological gains.

Trade‐offs among road–stream crossing upgrade prioritizations based on connectivity restoration and erosion risk control

“…Lastly, although joint D prioritization performed better than joint prioritization in achieving both objectives, optimizing each connectivity and non‐connectivity related objective separately could produce a greater outcome than combining different objectives into a single objective, as in scoring‐and‐ranking methods. We also acknowledge that although the joint methods perform relatively poorly at improving connectivity for migratory fish, the removal of midstream and upstream barriers with low passability might benefit resident fish species (King, O'Hanley, Newbold, Kemp, & Diebel, ).…”

The future of fish passage science, engineering, and practice

“…Under such a scenario, there will always be a need to make provision for fish passage, and better catchment planning of barriers is undoubtedly also needed (Winemiller et al., ). Great strides have been made in the development of models for planning catchment connectivity benefits and economic effects in relation to barrier addition or removal (Kemp & O'Hanley, ; McKay et al., ) but more can and is being performed to improve this by making such tools more accessible, biologically relevant and user‐friendly (King et al., ) to river managers internationally.…”

Commonalities in stream connectivity restoration alternatives: an attempt to simplify barrier removal optimization

“…, King et al. ). In basins where multiple aquatic organisms are of conservation concern, objective functions aimed to inform barrier removal for one group of species are unlikely to be representative of habitat needs of other species.…”

“…, King et al. ). Additionally, some studies have included the cost of barrier removal in multi‐objective optimization (King et al.…”