The plates number 160 to 360 on each side. Of course, most of us find it impossible to eat with our mouths open. But baleen whales are great at this. The whale eats by swimming open-mouthed, gathering large volumes of sea water, then forcing the water out and using the baleen to trap a big mouthful of little sea creatures. During the summer, the blue whale needs four tons of krill per day to survive.
Baleen whales tend to spend the summer in polar seas, where plankton blooms provide abundant food.
Humpback whales, for instance, spend much of year off the coast of New England and Canada. In addition to plankton and krill, the humpback will occasionally dine on herring, anchovies, sardines, cod and salmon. Their stomachs are usually empty in the winter months, evidence that the humpback is a seasonal feeder, eating constantly during the summer and spending the winter digesting. Or monarch butterflies. But don't forget to include whales on the list.