An Investigation of the Impacts of ponded pastures on Barramundi and other finfish populations in tropical coastal wetlands
Wild production of barramundi depends partially on nursery habitats located in tropical coastal wetlands. Modifications of these habitats have potential to impact barramundi populations (Russell and Garrett, 1985). Extensive areas of tropical coastal wetlands (including upper intertidal areas on coastal plains and in estuaries, brackish-water wetlands and riverine floodplains) have been modified by the development of ponded pastures and other pondage systems. The impacts of such developments on barramundi have not been documented despite considerable concern amoungst fisheries stakeholders regarding the entrapment and survival of barramundi in pondage systems.
Similarly, the widespread introduction of exotic species of water-loving grasses in ponded pastures has not been documented nor investigated. The invasion of these species in wetlands and water-courses represents a major change in wetland ecology. The impact of exotic grass species on the value of tropical coastal wetlands as barramundi nurseries is unknown.
Apart from the issues of barramundi entrapment and mortality, ponded pastures and other pondage systems may have potential benefits to fisheries production by increasing the area of wetland or by increasing the duration of inundation. These positive aspects of pondage systems have not been assessed but may provide an avenue to balance the fisheries needs with those of the agricultural sectors and other wetland users. This balance would require the development of wetland management strategies to facilitate barramundi survival and movement in ponded pastures.
The Queensland Government has established an interdepartmental ponded pasture steering committee to develop a policy on ponded pastures in response to considerable community concern over environmental issues associated with ponded pastures and the introduction of exotic grass species. Public and industry comments on a discussion paper produced by the ponded pasture steering committee identified the impact of ponded pastures on fisheries as a major issue. However, the formulation of a policy which adequately safeguards the interests of fisheries stakeholders has been hampered by a lack of information with respect to the impacts of ponded pastures on fisheries, particularly barramundi. It remains to be determined whether the modification of wetlands by embankments and by the introduction of exotic grass species represents a significant impact to barramundi production.
Information on the growth, survival and movement of barramundi in ponded pastures and other pondage systems is required to determine the nature of impacts on barramundi production. Such information is also required to establish a more informed discussion between the fishing industry and agricultural sectors. Ultimately, strategies are required for managing ponded pastures and other pondage systems to balance the needs of fisheries with the requirements of agricultural sectors and other wetland users.
