Eggstinction - the links between flow regulation and shortages of egg-laying habitat for stream insects

Andrew Brooks (Surface Water Science) in collaboration with PhD student Handoko Wahjudi (now working at BCS), Prof Barbara Downes and Dr Wim Bovill from The University of Melbourne, have recently completed a multi-year study investigating whether flow regulation inhibits the reproduction of stream insects by restricting egg-laying habitat downstream of dams.

Many species of freshwater insects require rocks that protrude from the water surface (emergent rocks) for egg-laying habitat (oviposition). This research found that egg laying was rare in regulated rivers (Tumut and Murrumbidgee rivers) because high flows submerged all emergent rocks during spring and summer, and low flow releases stranded rocks above the waterline during autumn and winter. In contrast, hundreds of emergent rocks and thousands of egg masses were regularly found at sites in the unregulated rivers.

This oviposition failure observed downstream of dams could have lasting effects on freshwater insect population sizes and distribution and may explain why some species are absent from rivers where flows are regulated for irrigation.

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