THE CETACEANS (DOLPHINS, PORPOISES, AND WHALES) are the pelagic (completely waterborne) mammals of the sea. There are 79 such species. The reproduction of the cetaceans is the typical mammalian reproduction via sexual intercourse, gestation of the young dolphin in the womb, and birth, under water. The cetaceans nurse their young, feeding them milk formed in mammary glands. The cetaceans are warmblooded, with a brain temperature of 37 degrees C (98.6 degrees F). The cetaceans have lungs and breathe air. Their blood is circulated by a four-chambered heart similar to that of the land mammals. Their muscles closely resemble those of the land mammals and are used for propelling them through the water by movements of their flukes.Most of the life of the cetaceans is spent under water, and only a small fraction of the time is spent at the surface to breathe and to rise up and look around. Some species leap out of the water whe-n it is safe to do so. The breathing act of a cetacean car, be seen as a spout: a column of water droplets combined with the air that they expel from their lungs. The water droplets are from seawater collected in the sacs just below the blowhole from which the air mixed with the water comes forth. The explosive expulsion of the air from their lungs sucks up this water, forming the spout. The cetaceans have exquisitely streamlined bodies of distinctive shapes.
At the front end of their bodies the dolphins have long beaks, which are their jaws. The true porpoises have more blunt front ends, as do the pilot whales and the sperm whales. Most species have a dorsal fin, from the six-foot-high dorsal fin of a male Orcinus orca down to the practically nonexistent dorsal fin of some species of river dolphins and baleen whales.
The home territory of most of the cetaceans is the oceans and seas of earth, which cover 71 percent of the planet's surface. A few species live in freshwater rivers (the Amazon, the Plata, etc.). Some of the seagoing cetaceans travel up freshwater rivers some distance (Tursiops in the St. Johns River of Florida, the Beluga up the Mackenzie River and the St. Lawrence River, etc.). Since the cetaceans are effectively independent of their environmental water, they can live quite safely in freshwater, as has been demonstrated experimentally with the bottle-nosed dolphin.
The cetaceans cannot drink seawater; their kidneys wili not concentrate the urine any more than the kidneys of humans or other land mammals will. All of the cetaceans' water comes from the metabolism of the fat in their diet, changing the fat to carbon dioxide, which is exhaled, and water, which is held in the tissues. In effect then, the cetaceans are desert animals depending upon the water derived strictly from their food.
In order to avoid the ingestion of seawater as they take in their food, they have two major methods of keeping the seawater out: in the case of the toothed whales, there is a sphincter in the back of the throat, a circular muscle that closes the back af the throat until food, fish' or squid is to pass into the stomach. This sphincter squeezes the salt water off the food morsel and prevents the accumulation of salt beyond the sphincter. The second mechanism is found in the baleen whales in which they open their huge mouths in the dense kril!1 (small shrimplike creatures growing in abundance mainly in the Arctic and Antarctic oceans), take in the krill plus the seawater, and move the seawater out through the strainer known as the baleen, catching the krill in the strainer. They then close the mouth, which now has no seawater in it, and swallow the krill. Thus do the cetaceans prevent the taking on of the large amounts of salt present in seawater. Physiological experiments with humans and other land mammals show that drinking seawater leads to dehydration unless it is diluted with freshwater by a factor of approximately ten times.
Experiments on captive bottle-nosed dolphins show that they will drink freshwater when it is presented to them from a hose. This drinking then leads to their not eating for a day or two. They then start eating again and stop drinking water. Apparentry, in their natural state they do not separate thirst from hunger. Drinking freshwater allows them to feel hunger separate from thirst for the first time.
The diet of the toothed whales, including the dolphins and porpoises, consists of fish and/or squid. Small squid are eaten by the smaller cetaceans, and giant squid are eaten by the largest of the toothed whales, the sperm whale. The largest of the dolphins, Orcinus orca, the so-called killer whale, eats large fish and seals and some old dolphins of smaller size. They have also been seen to eat parts of baleen whales that have been killed by man. Baleen whales subsist totally on krill. The larger the cetacean, the longer he or she can go without food after a prolonged feeding period. The bottle-nosed dolphin can go approximately a week without food; the killer whale can go approximately six weeks without food; and the largest of the whales, the blue whale, can go approximately six months without food. During the period of maximum feeding the cetaceans store the food in the form of fat. The fat is then converted into Ibiological energy plus carbon dioxide and water. After a cetacean has burned up all his fat, he can die from lack of water.
Most cetaceans can dive to fairly great depths, depending upon their oxygen capacity, which again depends upon their body size. The larger the cetacean the deeper it can dive without needing air. Before a dive most cetaceans take a series of rapid breaths, then fill their lungs and start downward by lifting their tails out of the water to let the initial impetus of the gravity pull upon their hindquarters. As they dive, their lungs collapse, their ribs cave in, folding along special joints along the sides of their body. The lungs collapse completely, driving the remaining air into the dead spaces within the skull. This trapped air in the dead space is not given access to the bloodstream. The collapse of the lungs and confining of the air out of contact with the blood means that the oxygen and the nitrogen of the blood are at the same partial pressure that they are at the surface at one atmosphere. No nitrogen is forced into the blood or into the fat of their bodies; the nitrogen in the fat is at equilibrium at one atmosphere not at the high pressures of the depths to which they dive. The cetaceans then cannot experience the diver's disease known as bends, or decompression sickness. Bends result from air combining with the blood at the high pressure in the depths, and then, when one returns to the surface with his high pressure nitrogen saturating the fat of the body, one has the bends. As one rises to the surface and lowers the pressure on the body and in the lungs, the nitrogen must come out of the fat and it comes out in the form of painful bubbles that can block the circulation to the lungs and to various tissues. In human divers, using only a snorkel and not an Aqualung, no bends are experiencedÑthey are breathing the way ;he whales do.
The cetaceans will not experience bends until some human fries to force them to use an Aqualung. Or until some human educes them to breathe air in an open diving bell or in an open ndersea house in which the air pressure is kept at the pressure of the water at that depth. Such experiments with dolphins or vhales could be very dangerous for the cetaceans in that they have had no experience with bends. However, they may be ntelligent enough to rise slowly so that they will not experience he bends.
Cetacean swimming is mostly in three dimensions: two horizontal dimensions and one of depth. Each cetacean adjusts his buoyancy in order to be in a neutrally buoyant condition at a iven depth. In the neutrally buoyant condition very little effort i needed to swim. One does not have to exert muscular force to move horizontally and to stay at the given depth. Dolphins have uch camplete streamlining that they can tow each other; one dolphin in the proper position with respect to the other, or one whale in the proper position with respect to the other, is towed long in the swimming pressure pattern of the active dolphin or hale. Such activities show the beautiful streamlining and the low level of friction of the cetaceans with the surrounding water. There are several mechanisms that enhance this lack of friction. The shape of the body is streamlined, but it is also a flexible shape. When a dolphin accelerates, one can see the shape of the body change to match the acceleration vortices generated in the water as the velocity is changed rapidly. Vertical hollows in a definite wave pattern are seen to move along the sides of the animal, shedding the vortices generated. The skin of all cetaceans emits a very fine oil continuously from the front of the animal to the rear. After a whale dives, one can see the oil slick on the surface of the sea. This oil has several functions; its viscosity does not change with temperature and remains very low in either warm water or very cold water. The oil layer on the skin thus provides slippage for the boundary layers of seawater close to the skin, thus reducing the friction of the skin against the water. The cetaceans are literally lubricated, streamlined objects. Experiments on a six-meter international racing yacht, which allowed oil to flow out over the hull, showed that the same principle could be applied to humanly constructed boats and increase their speed considerably.
