Speed Talk (5 mins) Australian Society for Fish Biology Conference 2022

A comparison of the effectiveness of three fishway designs for use in a large tropical river system (Speed Talk) (#110)

Lee Baumgartner 1 , Craig Boys 2 , Tim Marsden 3 , Jarrod McPherson 1 , Nathan Ning 1 , Oudom Phonekhampheng 4 , Wayne Robinson 1 , Douangkham Singhanouvong 5 , Ivor Stuart 1 , Garry Thorncraft 4
  1. Charles Sturt University, Albury, NSW, Australia
  2. Port Stephens Fisheries Institute, New South Wales Department of Primary Industries, Port Stephens, NSW, Australia
  3. Australasian Fish Passage Services, Fern Bay, NSW, Australia
  4. National University of Laos, Vientiane, Lao PDR
  5. Living Aquatic Resources Research Centre, Vientiane, Lao PDR

The development of dams and other infrastructure is placing significant pressure on the diverse and productive fisheries in many tropical river-floodplain systems, especially in systems like the Mekong River, where the fisheries are crucial for food security. Such structures prevent fish from accessing important feeding, spawning and nursery habitat. Fishways are becoming increasingly important for alleviating the impacts of barriers; however, there is still scant knowledge regarding their effectiveness for tropical river systems. We investigated the efficacy of three low-cost fishway designs for restoring degraded floodplain fisheries in the Lower Mekong Basin (LMB) in Laos: (1) vertical slot; (2) submerged orifice — 150 mm square opening; and (3) submerged orifice — 300 mm square opening. Field experiments were performed during the day and night to compare the abundance, biomass, species richness and size range of fish able to pass through the three designs. Passage of a total of 73 species was supported by each of the three fishway designs at a similar abundance, biomass, species richness and size range of fish, during both the day and night; though, the vertical slot design supported a different suite of fish species to that of the other two designs during the day. Our results suggest that each of these fishway designs could be effectively used to support the restoration of fisheries in the LMB and potentially other large tropical river systems with relatively diverse migratory fish communities and variable hydrological characteristics. Nonetheless, the vertical slot provides greater design and operational flexibility over the submerged orifice designs particularly in tropical systems with inherently variable hydrology. The final choice of fishway design ultimately rests on the fish species and size classes being prioritised for restoration and the hydrological features of the site.