Largest migrant

At around 20–30 m (65–100 ft) long and weighing c. 160 tonnes (176 tons), the blue whale (Balaenoptera musculus) is not only the largest animal in the world but also the largest migrating species, travelling thousands of kilometres from their Arctic or Antarctic feeding grounds to the warmer winter breeding grounds in the tropics. Blue whales feed on the rich supply of krill available in the polar regions, but must make an annual migration to the equator to breed, as their calves – born with just a thin layer of blubber – need milder waters to survive.

Even larger historical specimens of blue whale have been recorded by both length and weight:

Heaviest: A female blue whale weighing 190 tonnes (418,878 lb) and measuring 27.6 m (90 ft 6 in) in length was caught in the Southern Ocean on 20 March 1947.

Longest: A female blue whale landed in 1909 at the whaling station in Grytviken in South Georgia in the South Atlantic was documented as measuring "107 fot". Based on the Norwegian fot (or "fod") being equivalent to 313.74 mm (as of 1824), this gives a length of 33.57 m (110 ft 1.6 in).