The largest living animal, the blue whale (Balaenoptera musculus) which averages about 27 meters in length, has slowly recovered from whaling only to face the rising challenges of global warming, pollution, disrupted food sources, shipping, and other human threats. In a major new study, biologists have taken a stock of the number, distribution and genetic characteristics of blue whale populations around the world and found the greatest differences among the eastern Pacific, Antarctic subspecies and pygmy subspecies of the eastern Indian and western Pacific.