Statistics New Zealand no longer has data on the number of migrant departures to Australia after a decision made last year to make travel more seamless.
The government agency still has estimates of migrant arrivals from Australia, but it no longer has estimates of migrant departures to Australia, information obtained by Newshub under the Official Information Act has revealed.
"While we continue to have estimates of migrant arrivals from Australia - noting that these arrivals could be citizens of any country, including New Zealand - we no longer have (from November 2018) estimates of migrant departures to Australia.
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"The 'country of next residence' used to be collected by the departure card; there is no immediate data source to replace this information," Statistics NZ said.
The Government announced last year that from November 5, international travellers would no longer have to complete departure cards when leaving New Zealand. The purpose of the move was to improve the experience of travellers leaving the country.
"The removal of the departure cards aligns with international best practice, and will improve the experience of all travellers leaving New Zealand," Customs group manager of border operations, Terry Brown, said at the time.
But the removal of departure cards has cost the Government information on how many New Zealanders are leaving for Australia - information that was used to contribute to discussions about the 'brain drain'.
The amount of New Zealanders leaving for Australia has been a concern for some years, since the number started skyrocketing in the 2010s. In 2012, the number of Kiwis moving across the ditch almost doubled since 2007.
It became known as the 'brain drain' - the idea that New Zealand was losing its best and brightest workers to other countries perceived to have more opportunity, such as Australia, which is Kiwis' most popular destination for permanent migration.
When asked if he considered the statistical impact of ending departure cards, Immigration Minister Iain Lees-Galloway told Newshub he was "confident that Statistics New Zealand and our other government agencies have the data they need".
"The advice that we received was that the information is being gathered in other ways and that the departure cards were no longer useful as a source of statistical information, and therefore were really something that would get in the way of travellers."
He said he could not comment on the information disclosed to Newshub by Statistics NZ as he had not seen it. But he did say he was given "very consistent advice" that "that there are other ways of gathering that information".
One avenue currently being explored is to harness data from other countries of migrants arriving there from New Zealand.
However, Statistics NZ said that data often doesn't exist or is difficult to access, but is "feasible for Australia, given similarities to New Zealand in their border crossing system, data collection and statistical concepts".
Statistics NZ said it is "already in discussions" with the Australian Bureau of Statistics to access the "currently unpublished" data, but said the Australian data is "not available with the same timeliness as Stats NZ publishes New Zealand data".
The unavailability of information on the 'country of next residence' of migrant departures was a recognised impact when the decision to remove the departure cards was taken in 2018 - although the proposal had been underway for several years.
Briefing information provided to ministers when considering the decision to remove departure cards, and about the subsequent loss of some travel and migration information, is publicly available on the Ministry of Business, Innovation and Employment (MBIE) website.
It shows that a review confirmed the departure card is "an important source of statistical information on departing passengers".
The review found the cards were a "key component in measures of migration, tourism, and population estimation, through the collection of data which classifies departing travellers as visitors; New Zealand residents; or Permanent and Long Term migrants".
However, the review also found that while there would be a cost to removing the departure card, and some data may be "less timely than at present", removing them as a necessity for departing passengers was recommended.
"The preferred option would remove the requirement for departing passengers to fill in a card. It would also mean that migration statistics are published quarterly, rather than monthly as at present," it said.
Statistics NZ migration data shows that general annual migrant departures from New Zealand increased between 2016 and 2018 from 82,703 to 97,498. Migrant arrivals to New Zealand also increased in those years from 144,930 to 145,776.