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Whales, Dolphins and Other Marine Mammals
By George S. Fichter, Barbara J. Hoopes Ambler
St. Martin's PressCopyright © 2002 St. Martin's Press
All rights reserved.
About 120 of the more than 4,000 species of mammals live in the sea. These are the cetaceans (whales, dolphins, and porpoises), the pinnipeds (sea lions, walruses, and seals), the sirenians (manatees and Dugong), and two carnivores (the Sea Otter and the Polar Bear). The principal species in each group, shown in the family tree of mammals, are described and illustrated in this book. All marine mammals, even those so fishlike in appearance that they were once believed to be fish, share features that make them members of the class Mammalia.
All mammals are warm-blooded — that is, their body temperature is regulated internally and is independent of the environment. The young are carried internally by the female and nourished through an umbilical cord until their birth. They are then suckled (fed on milk) from their mother's mammary glands. Marine mammals also possess hair, which is as unique to mammals as feathers are to birds. Some marine mammals, such as the Sea Otter, Polar Bear, and several pinnipeds, have thick fur. Others, such as the cetaceans and sirenians, are covered with hair during an early stage of development but have a thick hide and only a scattering of bristles as adults.
Like their land-dwelling relatives, marine mammals have lungs and must breathe air. Whales, some of which are capable of diving more than a mile deep and can remain submerged for an hour or longer, must nevertheless surface to replenish their oxygen. Their blood is circulated by an efficient four-chambered heart. (Fish, in comparison, get their oxygen directly from the water by means of gills, and their less-efficient heart has only two chambers.) The brain of marine mammals is large and well-developed in contrast to the brain of lower classes of mammals.CHAPTER 2
WHALES, DOLPHINS, AND PORPOISES
All of the cetaceans, which total approximately 75 species, are exclusively aquatic, more completely so than are any other mammals. At no stage of life do they leave the water. Cetaceans range in size from the gigantic Blue Whale, the largest creature that has ever existed, to medium-sized dolphins and porpoises, some of which are only slightly more than 3 feet long. Typically a cetacean's head is joined to its body without a distinct neck. Except in a few species, the head cannot be turned independently. Characteristic of mammals, however, cetaceans do possess seven neck vertebrae, though much compressed. In some of the larger whales these are fused into a single disc only a few inches thick.
A cetacean's body is streamlined, or spindle-shaped, and in some species the head may be extended into a "beak." Many kinds have a definite dorsal fin consisting of a thick folded ridge of skin without a bony support. This feature adds to their general fishlike appearance. A cetacean's front legs are flippers, with no exposed claws or digits. A much reduced bony structure for a pelvic girdle is still in evidence internally, but external hind limbs are lacking. The tail, which provides the principal driving force for swimming, is extended into a broad horizontal appendage, separated into two flukes by a notch in the middle. The thin skin lacks hairs except for a few bristles around the mouth and on the belly in some species. Underneath the skin is a thick layer of blubber (mostly fat) that serves as a heat insulator as well as a food reserve. Blubber may be 2 feet thick in some of the larger whales and may account for more than 40 percent of the animal's total weight.
CETACEANS DEVELOPED from mammals that lived on land, their return to the sea commencing perhaps 60 million years ago. Fossil evidence is scarce, and so the precise and complete picture of cetacean evolution remains a bit of a mystery.
The sea has notable advantages over a land habitat. For one thing, food is more plentiful and easily obtainable. The sea is also a more uniform environment, lacking the large and sudden shifts in temperature that commonly occur on land.
An early sea-dwelling cetacean named Basilosaurus still had features marking it as closely related to the land dwellers. Some 60 feet long, it had an exceptionally long tail that made it so snakelike it was first classified as a reptile. Its hind legs had already disappeared, but its short, flipperlike front legs terminated in five digits. The nostril, or blowhole, was not yet centrally located on the top of the head. This unusual sea-dwelling mammal, now extinct, may or may not have been a direct ancestor of modern-day cetaceans.
Fossils show that the extinct forms of cetaceans had teeth differentiated into molars, canines, and incisors, like most mammals today. Modern cetaceans, some of which have a fossil history almost as long as the group to which Basilosaurus belonged, are divided into two suborders: the baleen, or whalebone, whales (Mysticeti) and the toothed whales (Odontoceti).
Toothed whales have simple teeth — conical, peglike, and all similar. Some species have several hundred teeth, others as few as two. Whales do not use their teeth for chewing but as effective tools for holding prey until it can be maneuvered into position for swallowing.
In baleen whales, teeth are lacking. Instead, these species have baleen, or whalebone, forming a screen that sieves tiny animals out of water taken into the mouth. These animals provide nourishment for the whales.
A CETACEAN BREATHES AIR through nostrils located on the very top of its head — one opening (or blowhole) in toothed whales, two blowholes in the baleen whales. The blowhole is closed by valves when the cetacean goes beneath the surface. Since there is no open connection between the nasal passages and the mouth as there is in other mammals, whales, dolphins, and porpoises can take water into their mouth with no danger of having it get into their lungs.
The instant a whale or other cetacean reaches the surface, the blowhole is exposed to the air and opened. The animal immediately exhales, or "blows." The heated air, under pressure and filled with water vapor, blasts into the cooler air of the atmosphere where it condenses into the characteristic "spout." In large whales, the spout may rise to more than 20 feet.
"Thar she blows!" was the jubilant cry of whalers on the lookout for their quarry. Experienced whalers could identify the kind of whale and its size by the shape and height of the spout. Whale watchers today can identify not only species but individuals by their spouts.
Some cetaceans can hold their breath for longer than an hour. Their very large lungs are stretched throughout the full length of their capacious abdominal cavity and are divided into as many as three times more air-holding sacs (alveoli) than are the lungs of land-dwelling mammals. Of equal importance is the fact that a cetacean can empty its immense lungs more completely than can land-dwelling mammals and then replenish them quickly with a fresh supply of air. In addition, the hemoglobin (red pigment) in a cetacean's blood has a greater capacity for holding oxygen than does the hemoglobin of land-dwelling mammals. All of the openings to the respiratory system — including the blowholes and the bronchial tubes — can be tightly shut by muscles.
CETACEANS GIVE BIRTH at sea. Typically only one calf is born; occasionally but rarely there are twins. In the larger species, there is a lapse of two years after the birth of the calf before the cow can bear again. In most cases, the calf is born tail first. As soon as the umbilical cord breaks, the young calf must get to the surface for its first breath of air. It can swim immediately, but often the mother gives it a boost in the right direction on this first and highly important trip. She will support the calf at the surface until it is fully adjusted to its sudden independence from the womb. Until this moment it has been warmed by the mother's amniotic fluid, but now it is in the cold sea.
Baleen whale mothers nurse their calves for about six months to a year. Toothed whales nurse for a year and a half to two years. A calf suckles under the water as the mother swims along slowly. Each mammary gland, one located on the right and one on the left just ahead of the tail, is hidden in a pocket of skin. The nipples are extruded by muscles during nursing.
Milk is produced in the glands and held in reservoirs. When the calf begins to suckle, the mother forces the milk out quickly. This shortens the time required for suckling so that the young can get back to the surface to breath. A cetacean's milk is very rich — about ten times higher in calories than cow's milk. The calf gets ample energy to sustain its rapid early growth. A baby Blue Whale, for example, may double its weight in as short a time as a week. (Human babies, by comparison, double their weight in roughly four months.)
SENSES OF CETACEANS developed to meet the demands of the aquatic habitat. In proportion to their body size, for example, cetaceans' eyes are small, protected from the salt water by a waxy secretion. Their vision is good but is not a highly important sense. Cetaceans have totally lost the sense of smell.
Although a cetacean lacks external ears, its hearing is acute. It can detect sounds for hundreds of miles in the sea. All cetaceans emit sounds for communication and some for navigation as well. The sounds are produced in the nasal passageways, not by the larynx. The "melon" of the Sperm Whale focuses or beams the sounds just as a lens focuses light.
The sounds vary with the species, but in general they are produced at two frequency levels. Sounds made at low frequency may be heard by people as squeaks, grunts, clicks, or whistles. These noises are used when the animals are "talking" to each other. The chatter is continuous when the animals are swimming in a group. The frequency of these sounds is typically no higher than 15,000 cycles per second, but they may be even lower than 1,000 cycles, both well within the range of human hearing. The haunting mating songs of the male Humpback Whale are at this frequency, and interestingly, the males vary their songs from year to year. Sometimes a male will sing for 20 hours or longer, with brief stops only for breathing. Are they singing what females most like to hear?
Another type of sound begins at a frequency of about 20,000 cycles per second, but this is mostly beyond the range of human hearing, which ends at about 25,000 cycles. Some sounds have been recorded at frequencies higher than 200,000 cycles per second. These high-frequency sounds, given off in short pulses, "echo" back to the animal from any objects in their surroundings. The echoes tell the cetacean where to find food and also guide it toward or away from objects. This echolocation system, similar to that used by bats and sonar-equipped ships, is remarkably accurate. A cetacean can determine not only the size and distance of objects but also their shape and structure. It is believed that migrating Bowhead Whales are guided around ice obstructions by scout whales traveling miles ahead of the herd.
MOST CETACEANS SLEEP occasionally while floating close to the surface. This is called "logging." As long as the top of the head is above the surface, they can continue to breathe while sleeping with no danger of drowning. Some of the larger whales sleep so soundly that ships run into them or they drift into shallows. Dolphins and porpoises seem to take frequent rests and naps but apparently never go into deep sleep.
SWIMMING in cetaceans is accomplished by up-and-down movements of the broad horizontal flukes, the body moving little from side to side. This is in contrast to fish, in which the tail moves from side to side and, for the majority (particularly the fast swimmers), the body supplies most of the power for swimming. Fish utilize their side fins for steering. Cetaceans steer by shifting the plane at which their flukes move through the water, though the paddlelike flippers assist in steering and also in balancing.
Most of the large whales cruise at 4 to 5 miles per hour. For short distances they may accelerate to 20 miles per hour, a few going even faster, but they do not maintain this speed for long. Many of the dolphins and porpoises, however, swim at 20 or even 30 miles per hour for short periods of time.
MIGRATION Many cetaceans make long migratory journeys between feeding and breeding areas. Best known of the migrants are the giant whales that were the quest of whalers. These hunters had to know where to look for whales in each season. They knew that the big whales spent their winters in warm or temperate waters, then returned to cooler waters in summer. These trips took the whales thousands of miles in a year.
The giant baleen whales find their food at least 20 times more plentiful in the cooler waters than in warmer seas. A big Blue Whale, for example, can stuff its stomach with as much as 4 to 8 tons of krill (small shrimplike crustaceans) per day, in this way building a reserve of energy, stored as blubber, for its months of fasting on the breeding grounds. Most of the whales take their trips in groups (pods or gams) made up of families, and they travel to and from the same general areas of the sea year after year.
WHALES WERE KILLED for subsistence by Eskimos and other shore-dwellers in early times. The people ate whale meat and blubber, used the oil as fuel for cooking and lighting, and made implements and decorative objects from the teeth and bones. Centuries ago whaling became an important maritime industry, but modern whaling methods ultimately exceeded the capacity of whales to replenish themselves. A number of whale species are now near extinction. In effect, the whaling industry put itself out of business by becoming too efficient and too greedy.
Some chroniclers say the first European whalers were the Norwegians, but most credit the Spaniards with making whaling a business. Soon the Dutch and the English became commercial whalers, too. Whaling was also important for centuries in Japan.
Soon after the settling of North America, whaling fleets from the Americas began to invade the seas. In the mid- 1800s, the United States' whaling fleet consisted of about 750 vessels, more than twice as many as the vessels of all other countries combined.
Nantucket, New Bedford, Gloucester, Marblehead, Provincetown, New London, Southampton, and many other towns on the east coast of the United States were built primarily around the whaling industry. Fortunes were made by some of the whale hunters and by those who merchandised whale products. Whalers took whatever whale was within striking distance of their harpoons, but the most sought after were Bowhead, Right, Humpback, Sperm, and Blue whales.
Whaling was a most dangerous and adventuresome enterprise. In the early days, whales were hunted from shore stations. Whalers sighted the animals that came close to the coast and then set out in small boats to chase them for the kill. When the hunters were close enough, they threw the heavy, sharp harpoon by hand, then attached ropes to killed or exhausted animals and towed them back to shore for processing.
Whales were also hunted in the open sea with larger vessels. Struck whales sometimes managed to capsize boats, hitting them with their broad, powerful flukes in their struggles to get free. Later, harpoons were fired from cannons, and their tips were fitted with explosives.
Whales were doomed when whalers took to the open sea in huge factory ships and fleets of fast, smaller boats that did the job of killing and towing the catch. Airplanes and helicopters were also employed to locate the whales and guide the whalers to their quarry. No whale was too large to be killed or processed. No whale was safe anywhere. No thought was given to conservation. The industry was ruled by greed.
Whole whales could be taken aboard on slipways at the stern of factory ships. They were immediately butchered with modern, mechanized equipment, and the products were refrigerated or rendered for oil. The ship then continued on its slaughter route. With whales nearing extermination in the Northern Hemisphere, the factory ships concentrated in Antarctic waters where the job of destruction was eventually nearly completed. In one season during the 1950s, factory ships processed more than 40,000 whales — compared to an annual production of fewer than 50 per season during the 1850s, before the days of factory ships.
Excerpted from Whales, Dolphins and Other Marine Mammals by George S. Fichter, Barbara J. Hoopes Ambler. Copyright © 2002 St. Martin's Press. Excerpted by permission of St. Martin's Press.
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