As part of FRDC 95/16, a preliminary model of the fishery for red-legged banana prawns in the Joseph Bonaparte Gulf has been developed. However, this model used estimates of growth and mortality from other prawn species, and from limited overseas studies on red-legged banana prawn fisheries that operate in different circumstances to the JBG fishery. The model will help to evaluate the impacts of changes in the seasonal pattern of fishing effort, as well as changes in the total annual fishing effort in the JBG. The model should also help to measure the effects of these changes in effort on both the yield and the spawning biomass of red-legged banana prawns. However, the results of the FRDC 95/16 model are sensitive to the values of growth and mortality that are used. A tagging study is necessary to obtain more accurate estimates of growth and mortality for the red-legged banana prawns in the JBG fishery.
The coastline of northern Australia is coming under increasing pressures from mining and tourism developments and the infrastructure, particularly ports, to support these activities. Currently, there are 9 proposals for major port or mining developments in the coastal zone of the Northern Prawn Fishery, and a further 6 proposals under assessment. One of these proposals is for the extractive dredging of diamonds in the Cambridge Gulf, in the JBG. Such mining would be very destructive of coastal habitats. The location and extent of the juvenile nursery areas need to be clearly defined to protect them from developmental degradation and to help explain any fluctuations in adult abundance caused by the effects of extreme environmental changes on the juvenile habitats.
Final report
This project has contributed to the ecologically sustainable management of the Northern Prawn Fishery (NPF) by providing information on the status of red-legged banana prawn stocks and the nursery habitats that support this fishery. It has achieved these outcomes by firstly completing detailed tagging studies to obtain robust estimates of growth and mortality for red-legged banana prawns. These estimates enabled per-recruit models for red-legged prawns to be revised and for the sustainability of the current fishing patterns to be assessed. The levels of estimated recruitment to the fishery are much lower than previously estimated and therefore the stocks may be more vulnerable to over-fishing than past assessments suggested. Secondly, broad-scale surveys across the inshore areas of the Joseph Bonaparte Gulf established that juvenile red-legged banana prawns are found in small, mangrove-lined creeks in the estuaries located 100 to 200 km south-east of the fishery (Fitzmaurice/Victoria Rivers to Cambridge Gulf). This means that changes in land-use that affect coastal habitats or water flow (e.g. the Ord River Stage II development) may affect the juvenile stages and the emigration of juveniles into the fishery.
Keywords: red-legged banana prawns, per-recruit models, growth, mortality, tagging, nursery habitats, mangroves, Joseph Bonaparte Gulf
