Kroon, F.J. and Ansell, D.H., (2006) A comparison of species assemblages between drainage systems with and without floodgates: implications for coastal floodplain management. Canadian Journal of Fish & Aquatic Sciences 86: 2400–2417.

Summary

Estuarine habitats, and in particular coastal floodplains and wetlands, provide essential nursery habitat for a large number of fish and prawn species, many of which are commercially and recreationally important. Human activities on coastal land, such as those associated with grazing, intensive cropping or industrial and residential development, can have detrimental downstream effects. For fisheries production in the estuaries of northern NSW, two of these land-based activities, drainage of acid sulfate soils and the alienation of significant areas of habitat, may have severe consequences for native fish.

In this paper, we examine the potential role of flood mitigation structures, in particular tidal floodgates, in depleting estuarine and inshore fisheries stocks in eastern Australia. We compared species assemblages (abundance and biomass) in ungated and gated drainage systems in the Clarence River floodplain over a one-year period. We subsequently determined which water and habitat quality variables were associated with the observed patterns in species assemblages.

Our results showed that the numbers and biomass of juvenile fish and prawns were significantly and consistently greater in drainage systems without floodgates compared to those with floodgates. The major variables of concern in systems with floodgates were: (i) the presence of a floodgate; (ii) elevated concentrations of nutrients; and (iii) the abundance of aquatic weeds.

The work described in this paper is part of a NSW Department of Primary Industries’ process to develop new management options for drainage systems with floodgates to improve water quality and fish passage in coastal catchments with acid sulfate soils.