fin whale

fin whale

 or finback whale or razorback whale or common rorqual

Swift, slender-bodied baleen whale (Balaenoptera physalus) named for the ridge on its back. It is 59–89 ft (18–27 m) long, with a triangular dorsal fin, short baleen, and several dozen grooves along its throat and chest. It is gray, with white on the underparts and on the right side of the lower jaw. It is found in oceans worldwide, in groups of a few to several hundred. It lives in polar waters in summer, feeding on crustaceans and small fishes, and moves to warmer waters in winter to breed. Once commercially valuable, it has been substantially reduced in numbers by overhunting and is now listed as an endangered species.