Ok, I am going to be the first one to bite! This obviously is something that is irritating non Australian ROV crews out there, even though these conditions were fought hard for a few years ago.
Perhaps if the UK ROV Industry had a Union that cared more about offshore workers than it does rail workers than the rates in the UK might start to rise one day.
In fact, the rates in Australia have not really gone up much since they did a few years ago, and it maybe time for more industrial talks!
Anyway, a quick google search using "foreign marine crew working in Australian waters" came up with a these answers:
"When a ship arrives in Australian waters and that arrival constitutes a break in the continuity of an international voyage because the ship will remain in Australia, Customs normally treats the ship as having been imported. Importation requires the owner to lodge a Customs entry.
Foreign sea crew lose their Maritime Crew Visa status 5 days after Customs entry/import. Foreign crew are required to depart Australia unless they hold an appropriate work visa which will usually be required to be applied for offshore."
Work Visas are not granted in Australia if an Australian Citizen is available and qualified to do the job.
If a foreigner is granted a work visa for Australia, then by law they must be paid the same wage as an Australian worker doing the same job.
Good on the Aussies!