Researchers believe that California blue whales have recovered in numbers and the population has returned to sustainable levels.
Scientists say this is the only population of blue whales to have rebounded from the ravages of whaling.
The research team estimate that there are now 2,200 of these giant creatures on the eastern side of the Pacific Ocean.
But concerns remain about their vulnerability to being struck by ships.
At up to 33m in length and weighing in at up to 190 tonnes, blue whales are the largest animals on the planet.
The California variety is often seen feeding close to the coast of the state, but they are found all the way from the Gulf of Alaska down to Costa Rica.
Writing in the journal, Marine Mammal Science, researchers from the University of Washington say the California blue whales are now at 97% of their historical levels.
Working out that this species is now back at its traditional numbers required some dogged scientific sleuthing.
Whaling nations concentrated their hunting efforts on the colder waters of the Antarctic and until the practice was banned in 1966 some 346,000 of the animals were killed by harpoon.
The numbers of blue whales caught in the Pacific was much lower, approximately 3,400 between 1905 and 1971.
Much of this hunting was carried out by Russian fleets.
However most of the data on the catches was kept secret under the Soviet regime. Scientists have only recently been able to get access to this information in the archives.