Production times of about 3 years for farmed abalone increases the risk associated with losses from disease or infrastructure failure. For this reason alone, there is an urgent need to address any factor that compromises health or production efficiency in abalone aquaculture systems. In this instance, other reasons necessitating completion of the proposed project include:
1. As the abalone aquaculture sector has grown, it has become apparent that high mortalities can occur during the summer months as water temperatures increase. For example, in 2000 one farm in Port Lincoln reported stock losses of up to 50 % (SA Industry, pers. comm.). The deaths are not isolated to one state or one species. Similar losses over summer have also been reported for farms culturing blacklip abalone in Tasmania (Mike Wing, Tas. Tiger Abalone, pers. comm.) and in Victoria (Mark Gervis, Southern Ocean Mariculture, pers. comm.). In Tasmania abalone mortalities are associated with rapid epithelial loss and the appearance of pustule like blisters on the footsole filled with a clear liquid. All mortalities are associated with elevated levels of Vibrio harvyi and cannabalism usually occurs once a mortality appears. As manipulation of water temperatures is not a commercially viable option in these production systems, other means must be devised to prevent losses of this magnitude. At present, farmers are addressing summer mortalities by reducing feeding rates to ensure maximum water quality. While this reduces mortalities, production levels suffer, hence other options are desirable.
2. The exact relationship between abalone mortality and decreased production levels, elevated water temperatures(stress)and nutrition is poorly understood. An understanding of these relationships will facilitate intervention to optimize health and production.