NOTE: Because of its small adult size, usually less than 30 feet (9.1 m), another member of the rorqual family, the minke whale, is included with the medium-sized whales in this guide. Features by which it may be distinguished from all other rorquals are discussed in the species account.
Further, inasmuch as the dorsal fin of the humpback whale is highly variable in shape, positive identification may require reference to the sperm whale (p. [57]), which, though the sperm whale has been classified with species without dorsal fin, has a rather distinct dorsal hump, particularly noticeable when the animal arches the back and tail to begin a long dive.
(40-65 feet [12-20 m] maximum overall length)
Without a Dorsal Fin
There are three species of large whales without a dorsal fin in the western North Atlantic Ocean. Two of these, the bowhead or Greenland whale, and its more widely distributed close relative the right whale, are baleen whales. The third, the sperm whale, is a toothed whale. The first two have relatively smooth backs without even a trace of a dorsal fin. The sperm whale has a humplike low, thick, dorsal ridge, which, from certain views, particularly when the animal is humping up to begin a dive, may be clearly visible and look like a fin. But because the profile of that hump and the knuckles which follow it are often not very prominent in this species, it has been classified with the finless big whales.