Oral Presentation Australian Society for Fish Biology Conference 2017

One-way traffic: Black Bream passage through a storm surge barrier. (#73)

Stephen Beatty 1 , James Tweedley 1 , David Morgan 1 , Joel Williams , Alan Cottingham 1
  1. Murdoch University, Murdoch, WA, Australia

Storm surge barriers are structures created across rivers, estuaries or tidal inlets to prevent coastal flooding.  However, along with halting upstream water movement, they also have the potential to impede the movement of fishes.  The Vasse and Wonnerup estuaries are located near the City of Busselton, Western Australia.  Both estuaries have downstream storm surge barriers to prevent the flooding of low-lying coastal land and have ‘fish gates’ integrated into them to enable fish passage during the low flow period. Owing to poor water quality that regularly occurs immediately upstream of the Vasse barrier, fish kill events have regularly occurred there during summer and autumn with Black Bream being particularly vulnerable.  However, no information existed on the movement patterns of Black Bream in the system nor on how fish passaged through the fish gates. This study aimed to determine the movement patterns and spatial and temporal distribution of the Black Bream within the Vasse-Wonnerup system using acoustic tags that were internally implanted in 41 Black Bream. The study revealed that Black Bream are highly mobile within parts of the system.  Key habitats identified include the Wonnerup Inlet and the Deadwater with habitat further upstream of the either surge barriers not often accessed even when passage through the gates was not impeded.   Crucially, the study revealed that the Black Bream that passaged through the Vasse fish gate only did so down a gradient (head loss), and once upstream of the barrier, did not (or could not) return downstream. Therefore, the study indicated that instead of the gates allowing the fish to escape from poor water conditions that occurred upstream, the Bream appear to be ‘stuck’, which initiating a review of the management of the fishgates for the mitigation of fish kills.