ASFB Home > 2007 > Spatial management of freshwater fish: A case study for Murray cod.

With the closure of commercial fisheries in the Murray Darling Basin, management of native freshwater fish mostly occurs for the purposes of conservation and recreational angling. The overall focus is now on the rehabilitation of populations, which is largely undertaken by State agencies and catchment bodies. While there is some coordination across States and assistance from Commonwealth agencies, management structures are largely determined by State borders and catchment management boundaries.

Rivers are longitudinal habitats and while there are smaller lateral movements into floodplain habitats most fish movement is up and down the river system. Such habitats pose some difficulties for management options such as protected areas, and if such areas are to be designated, they, along with other actions need to be established at the correct scale. This should be based on an understanding of the use of habitats at scales relevant to the fish rather than scales arbitrarily determined by humans. In order to effectively undertake this there is a need for knowledge of the fish species involved, taking into account the mobility and dispersal mechanisms of the different life stages of the species. This paper considers spatial issues that need to be considered for such management using the example of Murray cod. Murray cod is used as a case study as there is considerable new knowledge about its ecology, including movements. Murray cod is now listed as a threatened species (vulnerable) under the EPBC Act, although it remains a valuable angling species. As part of this listing process an extensive recovery planning process has been established. One of the high priority actions within this process has been the question of the scale of management units that should be established for this species.

Species management can occur at the population level which means a balance between recruitment, mortality and migration. For Murray cod this must include consideration of flows, fish passage and take by anglers. Adult Murray cod can move in the order of 100+ km, juveniles in the order of < 5km and larvae may potentially drift 100s of km depending on river flows. Another option is to manage population genetic units which are currently being determined for Murray cod, and this will be discussed. Management currently does not occur at these biological scales but is determined by institutional boundaries sometimes being undertaken at whole of river, catchment or river reach scales. Such issues need to be taken into account and there needs to be a practical amalgamation between operational management units and the scales that are required by the species.