_Porpoises and Dolphins_
Whales are known technically as cetaceans (pronounced seh-TAY-shuns); so
also are the various porpoises and dolphins which are mostly eaters of
fish. These are certainly the most numerous of all the cetaceans, making
up in numbers for their small size (6 to 8 feet). A few species range
between 20 and 30 feet. Porpoises and dolphins congregate around schools
of fish. Therefore fishermen are constantly on the lookout for a sight
of them. Since not infrequently the porpoises break the surface of the
water, leaping completely clear as if for a look around, they are not
difficult to locate. Porpoises and dolphins can be seen most frequently
in coastal waters where fish are most abundant. The porpoise and dolphin
families contain a great many species and it is beyond the scope of this
treatise to differentiate or name them all. However, these families
include such unique forms as the killer whale, narwhal, white whale (or
beluga as it is known to the Eskimos), and the pilot or black whale.
Generally one associates cetaceans with the ocean, so it may come as a
surprise to find that four dolphin species live in such major rivers as
the Amazon, La Plata, Ganges, and the Yangtze.
In dolphins, the mouth protrudes beyond the head as a beak or snout, and
in porpoises, the front of the head is blunt or gently rounded. It is
impossible to avoid confusion if one uses common names to separate the
various whales. Even though the word whale properly covers all the
kinds, to some it connotes only the larger species. Such a distinction
is wholly arbitrary, and cannot properly differentiate the natural
groupings of whales to which zoologists have assigned technical names.
It would be impossible to summarize the variety of common names which
many of the species have acquired through the centuries. The only
solution to this is to refer to the whales by the technical names which
connote relationship. (For readers who desire this differentiation, a
brief listing of the groups and representatives of each are provided in
an appendix.)
[Illustration: BALEEN WHALES]
BLUE WHALE (SULPHUR-BOTTOM WHALE)
FIN-BACK WHALE (COMMON RORQUAL)
GREENLAND RIGHT WHALE (BOWHEAD WHALE)
BLACK RIGHT WHALE
SEI WHALE
HUMP-BACKED WHALE (unlabelled in picture)
CALIFORNIA GRAY WHALE
LITTLE PIKED WHALE (LESSER RORQUAL)
PYGMY RIGHT WHALE
The Sperm Whale is given here for size comparison only.
[Illustration: TOOTHED WHALES]
SPERM WHALE
BOTTLE-NOSE WHALE
KILLER WHALE
PILOT WHALE (BLACKFISH)
CUVIER'S BEAKED WHALE
FALSE KILLER WHALE
TRUE'S BEAKED WHALE
NARWAL
WHITE WHALE (BELUGA)
PYGMY SPERM WHALE
BOTTLE-NOSE DOLPHIN
COMMON DOLPHIN
COMMON PORPOISE
_Squid Eaters_
The bottlenose whales are nearly toothless, feeding on squid like their
close relatives, the sperm whales. Porpoises and dolphins possess many
sharp conical teeth on both the upper and lower jaws, although the
narwhal which is related to them, breaks the rule by being toothless
save for the tusklike canine of the male. In this instance either the
right or left tooth elongates to produce an 8-foot spear. The other
tooth does not break the gum, and this is the condition found in the
female where both are rudimentary and not evident. The bottlenose whales
have but a single pair of teeth in the lower jaw, and their relatives,
the sperm whales, have 18-28 conical teeth per side on the lower jaw,
and these when fully grown may be 8 inches in length. Pockets are
provided in the toothless gum of the upper jaw to accommodate the teeth
when the mouth is closed.
The decline in the number of teeth in the sperm and bottlenose whales is
thought to be the elimination of structures which are no longer useful.
Whereas a porpoise's long mouth, bristling with sharp teeth, insures the
hooking and retention of a slippery active fish, a small mouth with a
few teeth is adequate to crush and slurp down the squid and the
weak-swimming fishes of the abyssal depths.
The sperm whale is the largest of the squid feeders, reaching 60 feet.
There is a diminutive counterpart, the pygmy sperm whale, which reaches
13 feet. It is exceedingly rare, whereas the sperm whale is abundant in
temperate and tropical seas. The beaked whales complete the groups
specialized for feeding on squid. Besides the modification of the mouth,
all these whales are noted for their ability to dive to great depths
where their food abounds. Not only can they dive to great depths, but
they can stay submerged for long periods--up to an hour? Sperm whales
have been found entangled in the submarine cables which were known to be
on the bottom at a depth of 3,000 feet. It is clear that such feeding
habits have opened up vast areas of the oceans to these species.
_Filter Whales_
The whalebone whales seem to have undertaken two different lines of
specialization in feeding: The right whales developed an enormous head
with a very large filter plate, whereas the rorquals are much more
streamlined with a small filter plate. The ability of the latter to
gather food is insured by the pleated throat. The right whales lack a
dorsal fin and are decidedly less streamlined. The rorquals have a
dorsal fin. There are two species which do not exactly fit in either
group. The humpback whale appears to be like the rorquals in that it has
a pleated throat and a suggestion of a fin. It is however, a very bulky
slow swimming species. The California gray whale, apparently, is
intermediate between the two groups and may be thought to be a survivor
of the ancestral stock from which both groups differentiated. It has
neither a pleated throat nor a fin. The gray whale, like the right
whale, has been slow to recover from whaling. It is likely that the
populations were never very large. Only the rorquals seem to have the
numbers needed for large whaling operations.