Hunted nearly to extinction during 20th century whaling, the Antarctic blue whale, the world's largest animal, went from a population size of roughly 200,000 to little more than 300. The most recent estimate in 2004 put Antarctic blue whales at less than 1% of their pre-whaling levels. A new study shows that, though these whales feed in different ocean basins, they appear to be a single population, information that will help conservation efforts moving forward.