Blue whales (Balaenoptera musculus), the largest animals on Earth, have been slow to recover since they were nearly hunted to extinction in the last century. But now, scientists say that the population of California blue whales, which numbers about 2200, is almost as high as it was in the early 1900s—a recovery that should be celebrated as a conservation success story. The scientists reached this conclusion after modeling the number of California blue whales, which range from the equator to the Gulf of Alaska, that were killed between 1905 and 1971. The overall take was a surprisingly low 3400, the scientists report today in Marine Mammal Science. In contrast, some 346,000 were harpooned in Antarctic waters. The difference in the population sizes reflects the difference between the two environments; the Antarctic is able to sustain a far larger number of whales. Now that the California blue whales are almost fully recovered, their population is growing more slowly. Whereas other researchers have suggested that ship strikes are adversely affecting these whales, this team says that the whales have simply reached the limits of their habitat, and it is this natural cause that best explains their current numbers.