Too fast for early whalers, the blue whale remained out of reach until the invention of the rocket-propelled harpoon in 1855. It wasn't until the turn of the 20th century however, and the start of industrial whaling, that they were taken in large numbers. At this time, some 239,000 blues lived in Antarctica, their stronghold. When the last blue was shot in March 1973, only 360 remained. Today, that number has crept to around 1,700.