Short Virtual Presentation & Digital Poster 10th Australian Stream Management Conference 2021

Quantifying the impacts of carp and waterbirds on aquatic vegetation within a regulated lowland river (#44)

Chris Jones 1 , Lyndsey Vivian 1 , Darren White 2 , Bryan Mole 1 , Ana Backstrom 3 , Zeb Tonkin 1 , Peter Menkhorst 1
  1. Arthur Rylah Institute for Environmental Research, Heidelberg, VIC, Australia
  2. North Central Catchment Management Authority, Huntly, VIC, Australia
  3. RMIT, Melbourne, Victoria, Aus
  • Aquatic vegetation provides many habitat benefits for aquatic and terrestrial fauna, but in some cases there are severe negative effects of fauna on those plants. European Carp (Cyprinus carpio) and waterbirds are known to have impacts on aquatic vegetation, but these impacts are rarely quantified and neither is the rate of recovery if those animals are excluded.
  • We installed eight paired (control/treatment) carp and waterfowl exclosures (2.4 x 2.4 m) in the Campaspe River, northern Victoria, at a site with known carp and waterbird populations to measure the changes in aquatic plant cover and richness when those taxa were excluded. Vegetation cover and richness were spatially mapped within each location on seven occasions from 2018 to 2021.
  • Overall, carp and waterbirds had significant negative impacts on aquatic and littoral vegetation cover and richness, but it was difficult to determine their individual impacts. Vegetation responses were highly variable depending on water depth, channel form, existing vegetation and substrate. Impacts on vegetation are likely to be highest where both taxa are present and where their activity is greater, e.g., shallow stream margins.
  • Waterway management that aims to benefit aquatic vegetation rivers needs to consider the separate and combined impacts of carp and waterbirds when setting objectives and expectations for outcomes. Specifically, flow management actions that facilitate recruitment and growth of aquatic vegetation as well as mitigating fauna impacts may help negate these impacts and enhance vegetation outcomes.
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