A navy commander is defending the decision not to board any of the three ships caught fishing illegally in the Southern Ocean, saying it was too dangerous.
Three fishing boats, falsely flagged to Equatorial Guinea, were found illegally fishing for toothfish in protected Antarctic waters last week.
The navy's offshore patrol vessel, HMNZS Wellington, was in the area to monitor whether fishing boats were complying with international laws.
It shadowed the three foreign ships but left the area after its crew was refused permission to board.
The Wellington's commanding officer Graham MacLean said once the illegal fishing ships were discovered, the patrol vessel's role was to gather evidence.
"We were able to exploit that element of surprise and catch them in the act of fishing and all the while capturing that as evidence, which as I said before is going to be used to target these guys - maybe not directly but their source, their enterprise and their networks around the world."
Lieutenant Commander MacLean said conditions were too dangerous for them to board, with five-metre swells, strong winds and icebergs.
"When the window of opportunity presented itself to conduct the boarding, the weather and the environment was outside the parameters of us being able to do so safely," he said.
"In conjunction with that, the vessels themselves were anti us getting on board so they did what they could do make that difficult for us."
Listen to Graham MacLean
University of Tasmania Antarctic Studies Institute academic Julia Jabour highlighted the importance of countries putting pressure on illegal toothfishing operations by preventing them from selling their catch.
Dr Jabour said the navy's efforts were worthwhile.
But she said it was not easy to maintain a naval presence in such remote waters so notices listed by Interpol alerting countries around the world to the poachers were very helpful.
"You don't send vessels after a catch like toothfish unless you are making a lot of money," she said.
"There's a good chance that they will be caught or more importantly, that ports will refuse entry to those vessels."
Lieutenant Commander MacLean said the evidence had been passed to the Ministry of Foreign Affairs and Trade.