One of Sea Shepherd's boats is leaving Wellington for its Operation Icefish campaign against fish poachers in the Southern Ocean.
Sea Shepherd says it's not afraid to stand in the way of toothfish poachers and millions of dollars in illegal profits when it leaves Wellington to protect the vulnerable Antarctic fish.
One of the activist organisation's ships, the Sam Simon, is sailing from the capital on Monday evening for its Operation Icefish campaign in the Southern Ocean.
The crew of 30 - including three Kiwis - and a second ship, the Bob Barker, will spend the next three months patrolling Antarctic and surrounding waters.
If it finds illegal fishers, it will confront them and attempt citizens arrests while also confiscating illegal fishing gear and alerting the relevant authorities.
Sea Shepherd's New Zealand director Michael Lawry says the operation switches the focus from whales to toothfish after the International Court of Justice found Japan's whaling programme was a commercial activity disguised as scientific research.
Illegal poaching of toothfish, sometimes referred to as "white gold" on the high seas, has existed for years, said Mr Lawry.
"This campaign fills a law enforcement void which is being exploited by illegal poachers," he said.
Prime Minister John Key says New Zealand plays a part where it can to monitor illegal poaching.
He would prefer that Sea Shepherd left the policing of the Southern Ocean to those with the legal authority to do something about it.
"Like whaling, we think there's a better way of dealing with that issue than on-scene confrontations," Mr Key told reporters on Monday.
Patagonian and Antarctic toothfish are species of cod icefish found at depths down to 3000 metres.
Antarctic toothfish have unique antifreeze-like proteins in their tissue to allow them to live in water where the temperature dips below zero, a feature not present in their Patagonian relatives who live in warmer water.
The highly prized fish can weigh 150kg each and are up to 2m long, and the Sea Shepherd says an illegal catch of 1500 tonnes can fetch up to $US83 million ($NZ106.7 million).