Standard Talk (15 mins) Australian Society for Fish Biology Conference 2022

Nineteen year study into the ecological succession of an estuarine wetland following the staged opening of floodgates (#126)

Craig A Boys 1 , Chook C Fowler 1
  1. NSW Department of Primary Industries, Port Stephens Fisheries Institute, Taylors Beach, NSW, Australia

Tidally active wetlands are important nurseries for fish and crustaceans; however, urban development and flood mitigation works have fragmented and destroyed much of this habitat, often leading to losses in fisheries productivity. In this talk I report on the results of a 19 year study (2004-2022) which demonstrates that many of these impacts are reversible with proper management. Eight floodgates that restricted tidal flushing of the Ramsar listed Hexham Swamp (Hunter River NSW) were incrementally opened to facilitate tidal flushing and nekton passage. Ecological succession and rehabilitation was evaluated under a full rehabilitation model (using treatment, control and reference sites), encompassing pre-floodgate opening, opening of one gate, three gates and finally all eight gates. Floodgate opening enhanced both water quality and nektonic assemblages relative to a control creek whose barrier remained in place. At rehabilitated sites we observed a doubling in species richness and significant increase in abundance of many commercially important species, including Eastern king prawn (15 times more), Yellowfin bream (62 times more), mullet (10 times more) and Silver biddy (19 times more). Recovery to a condition similar to ungated reference creeks was achieved once all eight gates were opened and tidal infiltration was maximised. The recovery has been sustained over the nine years that followed and largely resilient to both natural and anthropogenic forces. The study illustrated that reinstating tidal flushing can recover nursery habitats and enhance populations of economically valuable species.