Poster Presentation Australian Society for Limnology Congress 2013

Evaluating barriers to aquatic invertebrate dispersal: weirs and tributaries in the montane rivers of the Australian Alps (#213)

Andrew Brooks 1 2 , Ben Wolfenden 1 , Barbara Downes 2
  1. NSW Office of Water, Wollongong, NSW, Australia
  2. Department of Geography, University of Melbourne, Melbourne, VIC, Australia

Dams and weirs are a significant source of environmental degradation in rivers. One hypothesis explaining how they reduce species diversity is that dams and weirs are barriers (i.e. breaks in connectivity) to dispersal along rivers. Such connectivity can be pivotal to populations remaining extant, and also to restoration of degraded reaches. However, it is unknown whether and how dams or weirs block or impede dispersing species, hence diminishing the likelihood of successful downstream restoration. The aim of this project is to test whether and how dams and weirs (on tributaries and main stem channels) impede dispersal of aquatic invertebrates and thus compromise river rehabilitation using environmental flows. We first examined whether drifting invertebrates were impeded by 13 natural, slow-moving pools by measuring invertebrate drift entering and exiting each pool using drift nets (25 x 25cm opening, 1.5m long with 250┬Ám mesh). Second, we tested whether drift rates through natural pools differed from drift through the pool of Mowamba Weir when the weir was over-topping. Preliminary results show that deep, slow-moving natural pools are sinks for much of the invertebrate drift, and are potentially barriers to drift dispersal. Mowamba weir pool reduced the drift dispersal to a greater extent than natural pools for some species, suggesting that the weir is a partial barrier to dispersal and could limit downstream colonisation. Future studies will examine whether weirs on tributaries of regulated rivers (Geehi River, Snowy River) obstruct drift dispersal and hinder downstream colonisation in the tributary and mainstem of regulated rivers.