They feed mainly on 'krill' (or small crustaceans which look like shrimp about 2 inches long) and on small fish such as herring, mackerel, capelin, scad, sand lance, small salmon, and cod. The name krill originates from the Norwegian word "kril" which means "small fry of fish (1907)". In the cold Arctic and Antarctic waters, these krill are found in large close swarms. Humpback whales eat up to a ton of feed per day when they are in cooler waters to build up a thick fat layer, called "blubber". They live on this blubber during the winter months when they stay in warmer waters where less food is available. The blubber layer on a large whale can be up to 18" thick!

That is the argument of the Japanese lobbyists for commercial whaling, who claim that the whales will deplete all the fish stocks, but it is not true! Humpback whales are not able to eat big fish which we humans prefer (like tuna, perch or swordfish) because their throat only has a diameter of only 6-8 inches or the size of a cantaloupe! If a bigger fish came into its mouth, the humpback whale would have to spit it out to avoid chocking. The types of fish the humpback whales eat are not overfished, yet. The greatest danger to the fish supply comes from humans who are about to destroy global food supplies by overfishing.

Humpback whales have developed different hunting techniques. Sometimes they simply swim through a large swarm of krill with an open mouth taking in tons of water and krill. In order to be able to take up such masses in the mouth, the throat grooves expand greatly. The water exits the mouth through the baleen plates when the tongue is pressed to the roof of the mouth. On a large whale, the tongue alone can weigh 2 tons! The small crustaceans or fish are caught behind the baleen plates (see also: What are baleen plates?) and then swallowed. A very specific technique of the Humpback whale can be observed: sometimes four to six whales unite in a group, diving down and circling a swarm of krill or fish. While circling and slowly emerging to the surface, the whales discharge air so that a net of bubbles develops. These bubbles force the prey in the center of the circle and what looks like a circle of ascending bubbles emerges, resulting in a spectacular event where several humpback whales with open mouth suddenly appear at one time taking up what they caught in this net of bubbles. What fascinates researchers is the whales can control the bubble sizes. Small bubbles for small prey like krill and larger bubbles for fish! Researchers have also discovered that the feeding groups may be established friends that may feed together every year for a lifetime. Dr. Fred Sharpe discovered also that there appears to be a ‘senior' member who does a "siren call" and is also seen to be the first whale to the surface. More research is being done to try and unlock the secrets of feeding behaviors with humpback whales, the only whale on the planet known to use bubbles in this way.