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.
number of possibilities for the treatment of ballast water are being
explored (O'Hara 1999b); these include heat treatment (to 37-41°C -
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).
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