Blue whales are the largest mammals, and possibly the largest animal of any kind to have lived on Earth. A 33-metre long, 190-tonne whale has been seen, but most are smaller than this.

Blues were hunted to the brink of extinction during the 20th Century, before being protected in the mid-1960s.

The most recent abundance estimate for the Southern Hemisphere is 2,300 and there is evidence they are increasing annually by about 7%.

There are no good estimates for numbers in other areas, but there is some evidence of a population increase in the North Atlantic.