There is an urgent need to rehabilitate the stock of black bream in the Blackwood River Estuary and enable the stock subsequently to be sustained at a higher level than present.
There is thus a need to culture black bream, using brood stock from the Blackwood River Estuary, for (i) restocking that estuary and (ii) to confirm subsequently that released black bream survive in the estuary and make a significant contribution to the fishable stock.
The collection of baseline data on the stock of black bream in the Blackwood River Estuary is required to make comparisons between the status and biological parameters of black bream prior to restocking the Blackwood River Estuary and (1) those in other estuaries where substantial stocks of this species are still present and (2) those of the entire population in the Blackwood River Estuary after restocking.
Management will need to ensure that the fishery is regulated in order that the enhanced stock is sustained. The production of management plans will require a sound understanding of the biological parameters of age, growth and reproductive biology prior to and after the restocking. Information is also required on the catch rates and size compositions of recreational and commercial catches prior to and after restocking.
The results of this study show that hatchery-reared Black Bream can be used to enhance the stock of the population of this commercially and recreationally important species in the Blackwood River Estuary in which it has become depleted. An initial trial of different stains demonstrated that alizarin complexone was particularly effective for staining the otoliths (ear bones) of Black Bream. The mark on the otoliths, produced by this stain following immersion of hatchery-reared juveniles, was still visible to the naked eye 3.5 years later. Substantial numbers of the stocked Black Bream, which were introduced into the Blackwood River Estuary, were still living at the end of 3.5 years. On average, these individuals did not grow as rapidly as those in the wild population, and unlike the wild fish, not all stocked Black Bream attained maturity by 4 years of age.
However, they still grew at a rate that was greater than that in some other estuaries and many did reach maturity by 4 years of age. The Black Bream is thus a particularly good candidate for restocking an estuary as it completes its life cycle within these systems in south-western Australia and consequently any stocked fish are unlikely to move into other estuaries in this region. The ease and relatively low cost of culture of Black Bream and its hardiness and restriction to its natal estuary make the restocking of Black Bream a feasible and economically-viable proposition.
This study shows that restocking provides managers with a further and viable option for countering the effects of a decline in a stock of Black Bream in an estuary.
Keywords: This study shows that restocking provides managers with a further and viable option for countering the effects of a decline in a stock of Black Bream in an estuary.
The Western Australian Fish Foundation (WAFF) convened this workshop on February 26, 2007 at the Fremantle Maritime Museum to discuss the implications of the recently completed project entitled "Restocking the Blackwood River Estuary with the Black Bream Acanthopagrus butcheri", which was funded by the Fisheries Research and Development (FRDC) Corporation. The Workshop was convened by the WA Fish Foundation and sponsored by WAFF, the FRDC, Challenger TAFE, Murdoch University, the WA Department of Fisheries and the Blackwood Basin Group.
The aim of the Workshop was 1). to discuss the results and implications of the above study on Black bream and of the current environmental condition of the Blackwood River Estuary, 2). to consider whether it would be appropriate to continue restocking this estuary with Black Bream and 3). to determine what associated issues should be addressed in the future.
This report comprises the Synoptic Overview by Dr Peter Rogers followed by the Workshop Summary. A number of relevant speakers (see Appendix 1 for the Workshop Schedule) presented during the morning with the Workshop being conducted during the afternoon. Attendance was by invitation (50) and the list of the 48 participants can be found at Appendix 2. Power point presentations and/or summaries from the speakers can be found at Appendix 3 and additional Workshop Notes at Appendix 4.