Development of fish passage criteria for floodplain species of Central Laos

Location: Lao PDR

Duration: 2008 – 2009

Project Description: This project completed a proof-of-concept study to demonstrate the benefits of fishway construction for floodplain fish species of central Laos. A project team comprising scientists from Australia, and Lao P.D.R (in collaboration with Thailand) completed a series of experiments investigating the potential to use vertical slot fishways to restore connectivity between the Mekong River and a small floodplain wetland. The team constructed an experimental fishway facility to demonstrate the potential for this technology to rehabilitate floodplain fisheries in central Laos. This involved engaging the local community and gathering local support for the work through a series of meetings and workshops. Establishing a local network of contacts and actively involving villagers in the work led to the timely construction of an experimental facility which was installed at a floodplain regulator in Pak San (Central Laos).

Project Results: The project successfully achieved the objective of demonstrating that vertical slot fishways can provide passage for Lower Mekong fish species at low head weirs. Results suggested that a vertical slot fishway constructed on a 1:15 (6%) slope with small slot widths (150mm) and moderately sized cells (1000 mm X 1500 mm) was suitable for the majority of migratory species and size classes in Central Laos. However, some species which prefer fast flowing water may not ascend a fishway on this slope. Migration rates were substantially influenced by river flow which suggests that the design of permanent fishway installations must make careful consideration of local hydrology to perform efficiently. Fishway efficiency must be optimized at times of water level increases to ensure maximum fish passage rates. Careful consideration of these design aspects will provide functional fishways that have potential for widespread application.

Project Conclusions: The major outcome arising from this work is the realisation that development projects seeking to construct floodplain regulators could now provide fish passage by applying vertical slot fishways to the optimal design specifications. The species composition and total abundance of fish caught as part of this initial study demonstrate that a vertical slot fishway would be suitable at low head weirs, although other alternative low-cost designs should be considered to increase the potential for wider application at other wetlands throughout the Lower Mekong Basin. The long-term benefits of this work will help to rehabilitate wetlands and provide assist millions of people who rely on floodplain fisheries for food security and income.

Donor: Australian Centre for International Agricultural Research

Project Contact: Lee Baumgartner

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