While Australia was one of the first countries to bring in voluntary mid ocean exchange of ballast water, the effectiveness of this treatment is unknown. AQIS, the Federal agency that polices this practice, relies on ship logbooks, as there is no easy way of checking that the water in the ballast water tanks is really of oceanic origin.

 

A number of possibilities for the treatment of ballast water are being explored (O'Hara 1999b); these include heat treatment (to 37-41C  - sufficient to kill most larvae, spores and cysts if prolonged although these temperatures also tend to promote the growth of bacteria (e.g., cholera). Other options include a combination of UV light and filtration (expensive) or port-based filtration plants to purify ballast water. Chemical solutions are expensive and environmentally damaging. The management option in use today uses the environmental differences between the ballast water and destination port to minimise risk of introductions, e.g., by discharging freshwater into salt or vice-versa, tropical into colder water, or in mid ocean, etc. but this may not be effective for species with broad physiological tolerances. Flow-through exchange, where tanks are filled and emptied at the same time, is safer for most ships, although three tank volumes need to be exchanged to remove 95% of the original organisms (Rigby and Hallegraaef 1993).

 

A toxic dinoflagellate bloom in New Zealand, which closed their shellfish industry, resulted in a voluntary agreement between Australian and New Zealand ships that no ballast water would be taken on board in New Zealand waters or discharged into Australian waters. This agreement may have prevented the bloom from being introduced into Australian waters (O'Hara 1999b).



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Department of Environment and Heritage