Sources: The Sierra Club Handbook of Whales and Dolphins by Stephen Leatherwood and Randall R. Reeves (1983), and WWF international publications and materials.
Natural History
There are about 80 species of cetaceans, a group that includes whales, dolphins, and
porpoises. Of these, 12 species are commonly referred to as the "great whales" or "large
whales": the bowhead, northern right, southern right, pygmy right, blue, fin, sei,
humpback, Bryde's, minke, gray, and sperm whales. Cetaceans play an important role in the
life of the ocean: they serve as flagships and sentinels for the health and well-being of
the whole marine ecosystem. Cetaceans are air-breathing, warm-blooded mammals that bear
live young and nurse them on milk. The study of fossils indicates that cetaceans evolved
from four-legged, terrestrial ancestors that made their way back to the seas around 55
million years ago.
Cetaceans fall into two categories: baleen whales, or mysticetes (encompassing all
of the so-called "great whales" except the sperm whale), and toothed whales, or
odontocetes (including the sperm whale, smaller whales, and all dolphins and porpoises).
There are 11 species of baleen whales: blue, fin, sei, Bryde's, humpback, minke, northern
right, southern right, pygmy right, bowhead, and gray. They range in size from the compact
minke whale, whose average length is around 33 feet, to the gargantuan blue whale, which
can reach lengths of over 100 feet and weigh as much as 32 elephants! Distinctive
characteristics of the baleen whale include a symmetrical skull with no melon-the apparatus
used by odontocetes for echolocation-and a pair of nasal cavities, or blowholes, in stead
of the odontocetes' single blowhole.
Toothed whales, a diverse group of over 70 species, range in size from the approximately
5-foot-long harbor porpoise to the mammoth 60 (or so)-foot sperm whale. Some other examples
are the bottlenose dolphin, spinner dolphin, Indus river dolphin, orca (killer whale),
pilot whale, beluga whale, narwhal, finless porpoise, and the rather large family of beaked
whales.
Completely adapted to life in the water, whales breathe through blowholes (whales' "nostrils")
on top of the head, which allows them to take in air without interrupting swimming. Of the
great whales, the deep-diving sperm whale is the champion at holding its breath. The
longest recorded dive by a sperm whale lasted one hour and 13 minutes, and these whales can
descend to depths of more than a mile. Unlike fish, which swish their tails from side to
side, whales swim by pumping their tails vertically, and using their flippers to steer.
Whales that spend time in very cold water are insulated by a thick layer of blubber around
their bodies. Blubber also stores energy. Whales that migrate draw down these fat reserves
while transiting between their feeding and calving grounds. Most baleen whales are migratory-they
feed at high latitudes and bear their young in lower latitudes where the water temperature
is more hospitable to newborn calves with little blubber. Gray whales and humpbacks
undertake the longest migrations of all whale species. For example, the eastern North
Pacific gray whales feed in the Bering Sea between Alaska and Russia and travel all the way
to the Baja peninsula to have their calves.
Sources: The Sierra Club Handbook of Whales and Dolphins by Stephen Leatherwood and Randall R. Reeves (1983), and WWF international publications and materials.