Recreational fish stocking is widely practiced throughout Australia and has delivered considerable benefits to anglers and substantial economic flow-on effects have been previously documented in some fisheries (Rutledge et al. 1991). The long-term “success” of freshwater fish stocking in Queensland and other States is, however, contingent on demonstrating that it is an ecologically sustainable practice having no detrimental effects on wild populations and ecosystems. Some environmental groups and government agencies (e.g. Wet Tropics Management Authority) are now questioning if freshwater fish stocking is a sustainable activity and the Threatened Species Scientific Committee considered a nomination to list the introduction of live native or non-native fish into Australian watercourses that are outside their natural geographic distribution as a key threatening process. One of the criteria that fisheries managers now use for assessing freshwater fish stocking applications is the risk that they pose to local aquatic communities, although there is very little real information on the likely ecological and genetic impacts of native freshwater fish stocking activities to support this decision making process. This type of information is therefore urgently needed if our stocking industry is to adopt “world’s best practice” to ensure future sustainability.
These same concerns were expressed at a recent FRDC national expert workshop “Towards responsible native freshwater fish stocking” where the potential ecological and genetic impacts of fish stocking, particularly for barramundi and Murray cod, were nominated as the most pressing research and management issues. This proposed project and another being developed on Murray cod, are part of a coordinated national response to these critical issues.

Despite the large number of impoundments currently stocked in Queensland for recreational fishing, and the economic benefits resulting from this activity, almost no research has been conducted on developing strategies to maximise survival of stocked fry. Post-stocking surveys and creel surveys have given an indication of whether a given fishery is successful or not, but these surveys have not been designed to test any hypotheses on effective release strategies. To achieve maximum productivity at minimum cost freshwater fish stocking groups require reliable information that will assist them improve stocking procedures. This information will help stocking groups to be more cost effective in their operations by increasing the chances of stocked fish reaching a catchable size. To date impoundment stocking groups have been releasing fry without knowledge of whether different size classes of fry have different probabilities of survival. Similarly it is not known if point of release of stocked fry has any influence on survival rates. Properly conducted experiments which examine the relative survival of different size classes of fry and the influence of different release strategies on survival would be of immense benefit to recreational fishing groups in Queensland and other states. If for example small fry of one species (eg barramundi) were found to survive equally well as larger size classes, then it would make sense for the stocking groups to stock the cheaper smaller size classes. If larger size classes survive well, but smaller size classes have poor survival, then fish stocking groups will have better returns by stocking the more expensive larger size classes of fry. Similarly knowledge of whether point of release has any influence on survival for different stocked species will assist stocking groups to use their time and money efficiently.

It is clear from post-stocking and creel surveys that fry survive and grow better in some impoundments than others. A number of new dams are planned in various parts of Queensland. Knowledge of the environmental characteristics which influence the productivity and carrying capacity of impoundments will also benefit stocking groups by directing their efforts to productive locations or providing advice on actions which may enhance productivity or carrying capacity of impoundments. The current proposed project is a necessary first step to develop efficient stocking protocols and will lead to a follow up experiment/project examining in greater detail the success of stocked fisheries in a up to twenty impoundments. The subsequent project is expected to lead to predictions of the suitability of new impoundments for stocked fisheries and to strategies to improve the fisheries value of impoundments.