The food of the humpback is largely made up of krill - small shrimp-like crustaceans some 2-3cm in length. To catch them, the whale opens its vast mouth and takes in a large quantity of water full of krill. The 2-36 grooves below the throat help the mouth to expand more widely. Then the mouth is closed, and the water squirted out of the sides of the mouth, through the hanging curtains of hairs, called baleen, which trap the krill. When all the water has been expelled, the tongue is run over the baleen to remove the krill. The average humpback needs at least one tonne of food each day, containing about one million calories.
Humpbacks in the northern hemisphere have a more varied diet than those in the southern hemisphere, and feed on capelin, squid and shoaling fish such as mackerel and herring. They may use breaching and tail slapping to startle fish when hunting, and rising bubbles or 'nets' of air can confuse and enclose prey.
The humpbacks spend the spring, summer and autumn months in cold polar seas where there is plenty of food, but when these seas freeze over in winter, they migrate to warmer climates near the equator, where although there is little krill to eat, less energy is used up in staying warm. Migrations tend to hug the coasts, and during these movements they are sometimes seen in British waters.
Since the humpback feeds like a gigantic suction pump, it cannot be a very selective feeder. 'The Transactions of the National History Society of Northumberland' in 1831 records one humpback washed ashore dead at Berwick in September 1829. It reports that "on opening the mouth, six cormorants were found in it, another in the throat so that it was presumed that this whale had been choked in an attempt to swallow the birds." Perhaps the birds had been feeding on the same fish as the whale, and had also found their way into its vast mouth.Read More: Breeding