the sei whale ("balaenoptera borealis") is a dark-gray, stream-lined baleen whale that is found worldwide except in polar waters. it swims in small pods of 3-5 whales but larger groups may form at rich feeding grounds. it has very fine grey-black baleen that traps very small particles of food. it is a rorqual whale (a large baleen whale) that is similar to the bryde's whales.