Moving beyond fitting fish into equations: Progressing the fish passage debate in the Anthropocene

Abstract

Realization of the importance of fish passage for migratory species has led to the development of innovative and creative solutions (‘fishways’) to mitigate the effects of artificial barriers in freshwater systems in the last few decades. In many instances, however, the first move has been to attempt to engineer a solution to the problem, thus attempting to ‘fit fish into an equation’. These fishways are often derived from designs targeting salmonids in the Northern Hemisphere. They are rarely adequate, even for these strong‐swimming fish, and certainly appear to be unsuitable for most other species, not least for those of tropical regions. Fishway design criteria do not adequately account for natural variation among individuals, populations and species. Moreover, engineered solutions cannot reinstate the natural habitat and geomorphological properties of the river, objectives that have been largely ignored. This article discusses the most prominent issues with the current management and conservation of freshwater ecosystems as it pertains to fish passage. It is not intended as a review on fish passage, but rather a perspective on the issues related to fishways, as seen by practitioners.

Bidirectional connectivity via fish ladders in a large Neotropical river

“…We concur that protecting unimpounded stretches and unimpounded or lightly‐impounded tributaries are important components of an environmental management package. Our study endorses ladders as an element of this environmental management package, although ladders, especially in the Neotropical region, need engineering design advancements to better conform to the biological and behavioural requirements of native fish (Birnie‐Gauvin et al, ). The ladder at the Porto Primavera Dam allowed bidirectional migrations of adult fish, and sometimes multiple passes for the same individuals.…”

“…Fishways are constructed to reestablish connectivity between habitats of migratory species (Dodd, Cowx, & Bolland, ; Gouskov, Reyes, Wirthner‐Bitterlin, & Vorburger, ), and include elevators, locks, culverts, nature‐like channels, trap‐and‐haul operations, and ladders (Bravo‐Córdoba, Sanz‐Ronda, Ruiz‐Legazpi, Celestino, & Makrakis, ; Celestino et al, ; Clay, ; S. Makrakis, Miranda, Gomes, Makrakis, & Junior, ). Ladders have been built for over three centuries as a mitigation measure (Silva et al, ), and nowadays are still in constant development and their merits debated (Birnie‐Gauvin, Franklin, Wilkes, & Aarestrup, ). Fishways that allow upstream and downstream passage can ensure gene flow and maintain the evolutionary potential of species (Gouskov et al, ), and facilitate the connectivity and conservation objectives for target species (Godinho & Kynard, ; Kraabøl et al, ).…”

Coastal river connectivity and the distribution of ascending juvenile European eel (Anguilla anguilla L.): Implications for conservation strategies regarding fish‐passage solutions

“…It is therefore essential to determine whether or not these conservation actions facilitate the upstream dispersal of eels in the catchment in the intended way. The evaluation of FPSs is not generally implemented as a part of the installation (Birnie‐Gauvin et al, ); adequate evaluation usually consists of case studies using tagging methods to quantify attraction, entrance, and passage efficiency of different fish species (Noonan et al, ; Roscoe & Hinch, ). Tagging and telemetry studies give important insights into FPS design for optimizing attraction and passage; however, tagging small eels is difficult, which complicates the in situ evaluation of FPS efficiency.…”

Theory and practice to conserve freshwater biodiversity in the Anthropocene

“…These authors note that, even with this information, it is necessary to ensure the effective design and implementation of projects, and to be ready to identify where projects have limitations (e.g. the discussion of fish passageways by Birnie‐Gauvin, Franklin, Wilkes, & Aarestrup, ). Similarly, Langhans et al () draw attention to the importance of evaluating management strategies and quantifying their uncertainties.…”

“…Improvements in the development and implementation of flow protections are complemented by work under way around the world to improve fish passage at dams, including bi‐annual fish passage conferences (http://fishpassage.umass.edu/). However, as noted by Birnie‐Gauvin et al (), far more research is needed to make fish passage structures more effective, as fish passageways are typically designed using knowledge gleaned from rivers in the northern hemisphere and for strong‐swimming salmonids. These engineered solutions are not transferable to tropical rivers and the life‐histories of the fish inhabiting them (Reid et al, ; Roberts, ).…”