The endangered right whale is to get extra protection after a safe haven from shipping was set aside off Nova Scotia in Canada.
Right whales are near extinction, despite being protected since 1937
The International Maritime Organization (IMO) ratified a Canadian proposal to designate the 1,800-sq-km zone an "Area to Be Avoided" at a meeting in Denmark.
The voluntary restriction asks ship captains to steer around the area.
Collisions with container ships are seen as a key threat to right whales, thought to number just 400.
The new zone is in the Roseway Basin, south of the Canadian province of Nova Scotia.
It is close to a major shipping route between North America and Europe, and scientists say the slow-moving mammals have been killed in collisions with huge cargo vessels.
The restrictions will apply between 1 June and 31 December, when whales are known to congregate in the area.
Though the designation is voluntary, conservation groups say other such protected areas have seen a drop in shipping traffic.
The right whale is named as such because whalers considered them the "right whales" to hunt for their thick blubber, long baleen and because they floated when dead, making them easy to harvest. They can reach lengths of up to 18m (60 feet), weighing 30-80 metric tons.
Despite being protected since 1937 the right whale is close to extinction, with scientists estimating a global population of only 400.
Canadian parliamentarian Gerald Keddy said he was "delighted" his government's proposal had been backed by the IMO.
"Mariners will receive all the information they need to avoid collisions with right whales in the Roseway Basin. We are confident that the adoption of this proposal will have a significant positive impact on the right whales' road to recovery from the brink of extinction," he said in a statement.
Scientists with the Canadian Whale Institute called the move "a major step forward in helping the right whale to recover".