Many conservation efforts have been implemented to make this possible. Due to the secrecy and conflict with previous hunting laws and methods, the resulting small population of blue whales was unknown. Researchers therefore had to work out the present numbers from some scientific "sleuthing" and this could only take place recently due to having access to information from various archives.
Commercial whaling nations in the 1900s concentrated their hunting efforts on the colder Antarctic waters, whereby the practice was banned in 1966, when shockingly, some 346,000 were killed by harpoons during this sport. In comparison, the numbers caught in the Pacific were much lower, approximately 3,400 between 1905 and 1971.
At this time, however, there were no obvious signs as to what type of blue whales were being hunted. Now, research has shown there are two distinct groups: the California group and others that live near Japan and Russia.