A Cone Fishway Facilitates Lateral Migrations of Tropical River-Floodplain Fish Communities

Abstract

Fisheries in many tropical river-floodplain systems are under threat from physical obstructions caused by ongoing river infrastructure development. There is a growing need for innovative, cost-effective technologies to mitigate the impacts of these obstructions. This study examined the effectiveness of a new cone fishway for facilitating lateral migrations of river-floodplain fish communities in the Lower Mekong Basin in Lao PDR. We assessed the species richness, size range, abundance and biomass of fish able to pass through a cone fishway, using paired entrance and exit sampling during both dawn/day and dusk/night. Overall, a diverse range of taxa (76 species) and size classes (25–370 mm) ascended the cone fishway. The total size range of fishes observed at the fishway entrance was similar to that at the exit, although the fish at the entrance were significantly smaller (in length) than those at the exit, during both diel periods. Additionally, there were significantly higher abundances of fish at the entrance than at the exit, but there was no difference in total biomass, again for both periods. These results suggest that, with further development, the cone fishway design has considerable potential for facilitating the lateral migrations of diverse tropical river-floodplain fish communities at low/medium head infrastructure.

Multislot Fishway Improves Entrance Performance and Fish Transit Time over Vertical Slots

“…However, since VSFs generally require higher discharges to operate compared to pool-type fishways with bottom orifices and/or notches, operators may not share the same opinion, whereas they fail to meet one of the most challenging criteria in fishway design-the requirement to use as little water as possible for two main reasons: (i) construction costs are directly inflated with the design discharge; (ii) the more water volume is diverted, the less is available to hydropower production or other services provided by the dam, such as drinking water and irrigation [45]. Furthermore, in recent years, there has been a growing need to develop cost-effective fishways with lower turbulence that may operate with a broad discharge range [46]. In the present study, an experimental approach was conducted to assess entrance performance (entrance time and entry efficiency) and transit times of two Iberian cyprinids negotiating four distinct fishway configurations-using the same water depth in the pools-two VSFs and two MSFs, to gather insights about the fish passage behavior under different hydrodynamic scenarios and how conservation managers and dam operators may consider alternative mitigation cost-effective solutions capable of matching their goals.…”

Hydropower Development and the Loss of Fisheries in the Mekong River Basin

“…Since the mid-2000s, a multi-disciplinary research and development program in the Mekong Basin (summarized in Baumgartner et al, 2019a) has: documented the ubiquity of water management structures (Marsden et al, 2014); demonstrated methods for enabling fish to pass low-head barriers (Baumgartner et al, 2019b(Baumgartner et al, , 2020; outlined socio-economic benefits of improved fish passage (Millar et al, 2019); developed a decision making tool for assessing benefits-costs of fishways on low-head barriers (Cooper et al, 2019); and demonstrated scale-out of results through irrigation infrastructure rehabilitation projects in southern and northern Lao, funded by the World Bank and the Asian Development Bank, respectively (Baumgartner et al, 2019a). The program continues to generate data on the scaleout and cost-benefit of fishways to reconnect aquatic ecosystems in the Mekong, and more recently has initiated similar work in Myanmar and Indonesia.…”