Physical Characteristics of Baleen Whales
The most characteristic physical feature of baleen whales is that, rather than teeth, they have hundreds of baleen plates hung vertically from their upper jaws. The plates, with bristles on their inner edges, capture the krill the whales eat. A feeding baleen whale swims with its huge mouth open and engulfs several tons of seawater containing krill. Then the whale shuts its mouth, it presses its tongue against the back of the baleen bristles, and forces the water out of its mouth. This traps the krill on the baleen plates. In all whales, evolution yielded streamlined, fishlike mammals. Furthermore, their front legs became paddle-shaped flippers whose bones resemble jointed limbs and digits. In contrast, the external hind limbs disappeared, although in many cases their vestiges are found internalized. The horizontal tail flukes that propel whales are not anatomically related to hind limbs. They are boneless and shaped by fibrous and elastic tissues. Nor are flippers related to fish tail fins, which differ in composition and are orientated vertically. The whale body is surrounded by a thick blubber (fat) layer. This greatly enhances whale buoyancy, insulates, and is an excellent energy storehouse. The insulating ability of blubber may explain why whales living in warm waters have much thinner blubber layers than those living in cold waters. In addition, a whale’s soft rubbery skin lacks pores, sweat glands, and sebaceous glands. It is hairless, except for small patches on areas near the chin and atop the head. These hair patches support the theory that baleen whales evolved from animals having hair or fur. Whales, like all mammals, have lungs and breathe air through one or two nostrils, depending on species, located in a blowhole. Just prior to dives whales close their nostrils tightly. If kept submerged indefinitely, whales would drown. Whale nostrils are located on top of the head for functional convenience in diving. They connect directly to the lungs. Contrary to popular belief, a whale’s visible “spout” is not water. It is exhaled, warmed water vapor and spent air fromthe lungs, plus any water present in the depression around the blowhole. Four physiological adaptations allow whales to dive deeply and for prolonged time periods. First, they have more blood than land mammals and a huge capacity to store oxygen in blood and muscle. Second, each whale breath replaces 85 percent of the air in its lungs, compared with 15 percent in land mammals. Third, whales can resist the carbon dioxide buildup that triggers involuntary breathing in land mammals. Consequently, most baleen whales can hold their breath for an hour or more under water. Finally, they are able to restrict blood flow to various organs during deep dives, limiting oxygen flow to inessential sites. This protects the whale heart and brain from oxygen deprivation in long dives.
Special Senses and Baleen Whale Intelligence
Baleen whales have small eyes, lack external ears, and have brains much larger than those of humans. These physical characteristics have led to the belief that the whales use sound and hearing in thewayvision and smell are used by landmammals. Two kinds of sounds are made by baleen whales: echolocation and vocalizations. Both are thought to arise from air moving between nostrils and the nasal passages that lead to the lungs Echolocation sounds are thought to function like biosonar, as in terrestrial bats. That is, whale echolocation is perceived as the means by which they explore the world around them. On the other hand, vocalizations, such as the “songs of humpback whales,” are perceived as the language by which members of the same whale species communicate. It is thought that the whale identifies the size, distance, and other characteristics of an object by the directing sounds made in a whale’s head toward it and receiving sound waves that bounce back off it. Evidence for the role of echolocation is taken from observations made on whales in captivity. In addition, some beached whales have had parasites in their inner ears that lead scientists to believe that the whales ran aground due to losing the ability to echolocate shorelines and stay away from them. The great ability of water to carry and amplify sound waves is deemed to be the reason why cetaceans have been able to discard the external ear that land mammals developed to gather airborne sounds. Operation of this system of sensing would have obvious use in navigating and in the capture of prey in dark, often murky ocean water. There it would provide the means to scan by sound for the information almost all land mammals get by seeing. The unusual sensory capabilities of whales have given rise to considerable speculation as to their intelligence. This is stimulated by the observation that cetaceans are the only animals except elephants (with ten-pound brains) to have brains larger those of humans (three pounds). For example, an adult sperm whale has a twenty-pound brain. However, the relationship of brain size to intelligence, in this size range, is not clear. Supporting the contention of brain size paralleling intelligence, whales and dolphins show considerable capacity for learning when studied in captivity. Their great playfulness, intraspecies communalism, and the affectionate care of offspring make many people strong advocates of cetacean “language” and great intelligence. These concepts remain unproven.
The Life Cycle of Baleen Whales
Baleen whales reproduce in a fashion similar to that in other mammals. Adults enter a period of courtship. This includes side-by-side swimming, body nuzzling, and body rubbing. Copulation soon follows. The pregnant female carries her unborn young for ten to sixteen months, depending on whale species. Next, a large, very well-developed calf (or occasionally, two) is born underwater. Healthy whale calves can swim well at birth and immediately find the ocean surface, with no help from the mother.The calves nurse from two teats situated in a pocket located on either side of the mother whale’s genital opening. Whale milk is white and very rich in minerals, protein, and fat; as a result, the calves grow quite fast. Usually a whale calf that weighs one to two tons at birth doubles its weight in the first week. It is reported that nursing occurs very rapidly.Acalf approaches the mother whale, touches the nipple of the mammary gland, and milk immediately and copiously squirts into the calf’s mouth. Mother whales are reportedly quite affectionate to and protective of their offspring. Young whales are weaned between one and two years after birth, the age at which most of them leave their mothers. A whale is an adult, capable of reproduction, by six to ten years of age. The life spans of whales vary with maximumspecies size. The smaller species can live for thirty to forty years. The largest species can live for as long as eighty years. As with all other wild animals, not all whales—in fact, relatively few of them— survive to the ripe old ages noted.
Baleen Whales as an Endangered Species
Past, uncontrolled whaling reduced the numbers of almost all baleen whale species so much that they are perceived as being endangered. At first, quotas on whales were set by the International Whaling Commission (IWC) for the purpose of managing whales so as to allow the continuation of the whaling industry. By the early 1990’s, most major whaling nations belonging to the IWC had stopped whaling. It is hoped that these actions, in the absence of clandestine whaling, will allow baleen whales to make a comeback by natural increase. Only the future will tell whether this will happen.
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