- Email: [email protected]
Baleen
78
B
Baleen
without the risk of overstimulation. In cetaceans, on the other hand, little neck motility and ineffective head stabilization combined with acrobatic locomotion implies that the semicircular canal system is likely to experience substantially stronger rotatory input (resulting from movements of the entire body) than in terrestrial mammals of similar body size. The small arc size of cetacean canals may therefore reduce the sensitivity to match the high levels of uncompensated rotations, and avoid overstimulation of the canal system. The loss of canal sensitivity, in response to streamlining of the body, is arguably less critical in an aquatic environment than in, for example, an arboreal setting where less accurate sensory clues easily impair locomotor control. Moreover, less effective stabilization of the eyes is not critical in cetacean navigation which is driven by sonar rather than visual clues. Kinematic analyses of cetacean head motion in comparison with terrestrial mammals of similar size will be essential to test the hypothesis that the cetacean canal system experiences stronger rotatory input. Sirenians do show reduced neck motility, but not the extreme semicircular canal reduction of cetaceans. However, they are slow and cautious in their swimming, so that fast and effective head stabilization is not a factor of importance. Their canal size is at the lower end of the non-cetacean mammalian variation, as are terrestrial species that are slow and cautious in their locomotion. Among pinnipeds the semicircular canals of phocids and otariids are different in arc size from terrestrial carnivores, but none show the dramatic size reduction seen in cetaceans. This is expected because they all have motile necks enabling effective head stabilization. Likewise, that phocids have larger canals than terrestrial carnivores is expected, as they are particularly agile in their swimming, and thus follow the normal pattern seen among non-cetacean mammals. However, the smaller anterior and posterior canals of otariids are more difficult to understand. Otariids use a different mode of propulsion than phocids, a bird-like forelimb flight stroke, as opposed to bilateral hind limb undulation, and with a longer neck their center of gravity is located further forward. However, it is not clear how the otariid’s smaller canals with reduced mechanical sensitivity relates to either their locomotor pattern or their body plan.
of a baleen whale. The word derives from the Classical Latin Balaena and ultimately from the Greek Φα´λλαινα [phallaina], “whale.” Baleen plates are suspended from the whale’s palate and are arranged in a row down each side of the mouth, extending from the tip of the rostrum back to the esophageal orifice. The left and right sides are separated by a prominent longitudinal ridge along the midline of the palate. In the rorquals, the two sides are continuous around the tip of the palate, but in the other species the two rows are not confluent. Depending on the species, each “side” of baleen may contain anywhere between 140 and 430 plates. The plates are transversely oriented, and are spaced 1 or 2 cm apart, leaving a narrow gap or slot between adjacent plates. The plates are roughly triangular, with their horizontal basal edges embedded in the palate, their near-vertical labial edges facing outward, and their oblique, fringed lingual edges facing the inside of the mouth. Each plate is slightly curved, with its convex side facing forward, so that its labial edge is directed slightly backward; when the whale is swimming forward,
See Also the Following Article Sense Organs, Overview
References Spoor, F., and Thewissen, J. G. M. (2008). Balance: Comparative and functional anatomy in aquatic mammals. In “Senses on the Threshold” (J. G. M. Thewissen and S. Nummela, eds), Chapter 16. University of California Press, Berkeley, California, USA. Spoor, F., Bajpai, S., Hussain, S. T., Kumar, K., and Thewissen, J. G. M. (2002). Vestibular evidence for the evolution of aquatic behavior in early cetaceans. Nature 417, 163–166. Spoor, F., Garland, Th., Krovitz, G., Ryan, T. M., Silcox, M. T., and Walker, A. (2007). The primate semicircular canal system and locomotion. Proc. Nat. Acad. Sci 104, 10808–10812.
Baleen DALE W. RICE
T
he term baleen (also called whalebone) is a mass noun that refers collectively to the series of thin keratinous plates (“baleen plates,” Fig. 1) that make up the filtering apparatus in the mouth
Figure 1 Parasagittal section through the palate of a sei whale (Balaenoptera borealis), at about midlength of the rostrum, showing the bases of several baleen plates. Anterior is to the right. See Fig. 2 for details.
Baleen
Corium Epithelial layer Pulp
Cornified cortex Cornified medulla
Gum tissue
Figure 2 Magnified section of the specimen in Fig. 1, showing the structure of the roots of the baleen plates. this arrangement helps to direct the flow of water through the interplate gaps from the mouth cavity to the exterior side of the baleen row. The sizes of the plates are smoothly graded, with the longest ones half to two-thirds of the way back from the tip of the rostrum, and only rudimentary ones at the anterior and posterior ends of the row (Williamson, 1973; Pivorunas 1976, 1979). Each baleen plate is made up of a middle layer, the medulla, which is sandwiched between the thin, smooth outer layers, or cortex (Fig. 2). The medulla consists of a mass of fine, hollow, hairlike keratinous tubules which run parallel to the labial side of the plate, and terminate along the lingual side; the tubules are embedded in and cemented together by a horny matrix. Evolutionarily, plates presumably originated by modification of the transverse ridges present on the palates of many terrestrial mammals. In whale fetuses the baleen first appears as a series of crosswise ridges along each side of the palate. The palatal tissue of baleen whales is arranged in three layers. The basal layer, several centimeters thick, is the corium. This is overlain by a thin epithelial layer only a few millimeters thick. The outermost epidermal layer, several centimeters thick, is simply called the gum tissue. The corium gives rise to, and is continuous with, the medulla of each baleen plate, whereas the adjacent epithelial layer is deflected downward to produce the cortical layers of each plate. The dense, rubbery gum tissue does not contribute to the formation of the plates, but simply fills the spaces between their bases, where it provides them a firm support. As each plate grows downward, its cortical layers become cornified sooner than the medulla does. This leaves the first few centimeters of the base of the plate with a layer of soft, highly vascular, corial tissue sandwiched between the keratinous outer layers; this soft layer is often called the pulp, by analogy with the pulp in mammalian teeth (Utrecht, 1965). In life, baleen plates are extremely tough and flexible, but once removed they soon become brittle and are easily fractured. Throughout the life of the whale its baleen plates grow continuously at their base, and wear away along their lingual margin. The cortex and the matrix of the medulla erode away first, freeing the ends of the fibrous tubules for a distance of about 10–20 cm. The freed tubules form a hairy fringe along the entire lingual side of the plate. The fringes of each plate lie back across the lingual edges of the plates
79
immediately behind them, the whole forming a dense hairy mat that covers the internal apertures to the gaps between the plates. This mat effectively filters out the food organisms while allowing the water to flow out of the whale’s mouth through the gaps. Like human fingernails, the thickness of the baleen plates varies with the nutritional state of the whale. Alternating periods of summer gorging and winter fasting leave a regular series of visible growth zones on the surfaces of the plates. These zones have been used to infer the ages of whales, but because of the constant wear, it is rare for more than five or six zones to remain in a plate (Ruud, 1945). A claim that evidence of individual ovulations could be detected in the growth patterns of baleen plates was never confirmed (Utrecht-Cock, 1965). The number of baleen plates per side, and their maximum size, shape, color, and other physical attributes are diagnostic for each species of whale. The right whales (family Balaenidae) with their narrow, highly arched rostrum have 250–390 narrow and extremely long plates, about 0.15–0.25 m. wide and up to 2.50 m. long in the black right whales (Eubalaena spp.) and 4.00 m. in the bowhead whale (B. mysticetus); they are black with a fine whitish fringe. The pygmy right whale (Caperea marginata; family Neobalaenidae) has about 230 narrow, short plates up 0.70-m long and 0.12-m wide; they are white with a black labial margin. The gray whale (Eschrichtius robustus; family Eschrichtiidae) has 140 thick but narrow and short plates, up to 0.10-m wide and 0.50-m long; they are white or ivory in color, with a coarse white fringe that resembles excelsior. The rorquals (family Balaenopteridae) with their wide, flat rostrum, have 270–430 plates with a basal width 50–95% of their length, which varies from about 0.20 m in the small minke whales to 1.00 m in the huge blue whale. Each species of rorqual has a different color-pattern on its baleen plates: humpback (Megaptera novaeangliae)—black with dirty-gray fringe; northern minke (Balaenoptera acutorostrata)—white, sometimes with a narrow black stripe along labial margin; Antarctic minke (B. bonaerensis) and Omura’s (B. omurai)—white with a wide black stripe along labial margin; Bryde’s (B. edeni)—black with light gray fringe; sei (B. borealis)—black with fine, silky, white fringe; fin (B. physalus)—gray and white longitudinal bands, with fringe the same colors; blue (B. musculus)—solid black with black fringe. All of the species of Balaenoptera except the blue whale usually have at least a few all-white baleen plates at the tip of the rostrum, mostly on the right side; this asymmetry is most prominent in the fin whale and Omura’s whale. In the nineteenth century, the long baleen plates of the bowhead and right whales were much in demand for uses where a tough but limber material was needed, so they were the most valuable product of the whale fishery. Landings of whalebone at United States ports reached their highest in 1853, with 5,652,300 pounds worth $1,950,000. The last year that any baleen reached the commercial market was 1930. Much of it was made into umbrella ribs, corset busks, and hoops for skirts. The fibrous fringes were used for brooms and brushes (Stevenson, 1907).
References Pivorunas, A. (1976). A mathematical consideration on the function of baleen plates and their fringes. Sci. Rep. Whales Res. Inst. 28, 37–55. Pivorunas, A. (1979). The feeding mechanisms of baleen whales. Am. Sci. 67, 432–440. Ruud, J. T. (1945). Further studies on the structure of the baleen plates and their application to age determination. Hvalrådets Skrifter 29, 1–69. Stevenson, C. H. (1907). Whalebone: Its production and utilization. Bur. Fish. Doc. 626, 1–12.
B
80
B
Baleen Whales (Mysticetes)
van Utrecht, W. L. (1965). On the growth of the baleen plate of the fin whale and the blue whale. Bijdr. Dierk. 35, 1–38. van Utrecht-Cock, C. N. (1965). Age determination and reproduction of female fin whales, Balaenoptera physalus (Linnaeus, 1758) with special regard to baleen plates and ovaries. Bijdr. Dierk. 35, 39–100. Williamson, G. R. (1973). Counting and measuring baleen and ventral grooves of whales. Sci. Rep. Whales Res. Inst. 25, 279–292.
Baleen Whales (Mysticetes) JOHN L. BANNISTER I. Characteristics and Taxonomy
T
he baleen or whalebone whales (Mysticeti) comprise one of the two recent (non-fossil) cetacean suborders. Modern baleen whales differ from the other suborder (toothed whales, Odontoceti), particularly in their lack of functional teeth. Instead they feed, on relatively very small marine organisms, by means of a highly specialized filter-feeding apparatus made up of baleen plates (“whalebone”) attached to the gum of the upper jaw. Other differences from toothed whales include the baleen whales’ paired blowhole, symmetrical skull, and absence of ribs articulating with the sternum. Baleen whales are generally huge (Fig. 1). In the blue whale, the largest known animal grows to more than 30-m long and weighing more than 170 tons. Like all other cetaceans, baleen whales are totally aquatic, and like most of the toothed whales, they are all marine. Many undertake very long migrations, and some are fast swimming. A few species come close to the coast at some part of their life cycle and may be seen from shore; however, much of their lives is spent far from land in the deep oceans. Baleen whale females grow slightly larger than the males. Animals of the same species tend to be larger in the Southern than in the Northern Hemisphere. Within the mysticetes are four families: (1) right whales (Balaenidae, balaenids); (2) pygmy right whales (Neobalenidae, neobalaenids); (3) gray whales (Eschrichtiidae-eschrichtiids); and (4) “rorquals” (Balaenopteridae, balaenopterids). Within the suborder, 14 species are now generally recognized. Their relationships, including their relationship to terrestrial ungulates, are indicated in Fig. 2. Right whales (Balaenidae) are distinguished from the other three families by their long and narrow baleen plates and arched upper jaw. Other balaenid features include, externally, a disproportionately large head (approximately one-third of the body length), long thin rostrum, and huge bowed lower lips; they lack multiple ventral grooves. Internally, there is no coronoid process on the lower jaw and cervical vertebrae are fused together. Within the family are two distinct groups—the bowhead (Balaena mysticetus) of northern polar waters (formerly known as the “Greenland” right whale), and the three “black” right whales, Eubalaena spp. of more temperate seas, so called to distinguish them from the “Greenland” right whale. All balaenids are robust. Pygmy right whales (Caperea marginata) have some features of both right whales and balaenopterids. The head is short (approximately one quarter of the body length), although with an arched upper jaw and bowed lower lips, and there is a dorsal fin. The relatively long and narrow baleen plates are yellowish white, with a dark outer border, quite different from the all-black balaenid baleen plates. Internally, pygmy right whales have numerous broadened and flattened ribs.
Gray whales (Eschrichtius robustus) are also somewhat intermediate in appearance between right whales and balaenopterids. They have short narrow heads, a slightly arched rostrum, and between two and five deep creases on the throat instead of the balaenopterid ventral grooves. The body is robust. There is no dorsal fin, but a series of 6–12 small “knuckles” along the tail stock. The yellowish-white baleen plates are relatively small. Balaenopterids comprise the seven whales of the genus Balaenoptera (blue, B. musculus; fin, B. physalus; sei, B. borealis; Bryde’s, B. edeni; Omura’s, B. omurai; common minke, B. acutorostrata, Antarctic minke, B. bonaerensis), and the humpback whale (Megaptera novaeangliae). All have relatively short heads, less than a quarter of the body length. In comparison with right whales, the baleen plates are short and wide. Numerous ventral grooves are present, and there is a dorsal fin, sometimes rather small. Internally, the upper jaw is relatively long and unarched, the mandibles are bowed outwards and a coronoid process is present; cervical vertebrae are generally free. All eight balaenopterids are often known as “rorquals” (from the Norse “rørkval, whale with pleats in its throat”). Strictly speaking, the term should probably be applied to the seven Balaenoptera species, recognizing the rather different humpback in its separate genus, but many authors now use it for all eight balaenopterids. Baleen whales are sometimes called “great whales.” Despite their generally huge size, some of the species are relatively small, and it seems preferable to restrict the term to the larger mysticetes (blue, fin, sei, Bryde’s, Omura’s, humpback) together with the largest odontocete (the sperm whale, Physeter macrocephalus). Reviewing the systematics and distribution of the world’s marine mammals, Rice (1998) drew attention to the derivation of the Latin word Mysticeti, and clarified the status of a variant, Mystacoceti. He described the former as coming from Aristotle’s original Greek mustoketos, meaning “the mouse, the whale so-called” or “the mousewhale” (said to be an ironic reference to the animals’ generally vast size). Mystacoceti means “moustache-whales,” and although used occasionally in the past (and more obviously appropriate for whales with baleen in their mouths) has been superseded by Mysticeti. Within the suborder, 14 species are now generally recognized. Although Rice believed that all right whales belong with the bowhead in the genus Balaena, recent genetic analyses have recognized three separate right whale species, in the genus Eubalaena: in the North Atlantic (E. glacialis); in the North Pacific (E. japonica); and in the Southern Hemisphere (E. australis). Indeed, Eubalaena is the only mysticete genus where separate species are recognized in each hemisphere. The taxonomic status of Bryde’s whales is confused. Currently one species is recognized (B. edeni) but it has several forms, at least one of which may be a separate species. The “ordinary” form has two distinct sub-forms—offshore and inshore. Another animal, B. brydei, was described from specimens taken off South Africa, but subsequently accepted as the same species as B. edeni. The situation has not been helped because the location of the type specimen of edeni was uncertain until recently and its genetic make-up has yet to be determined. A further similar but smaller species, Omura’s whale, B. omurai, was described in 2003, and recently accepted (Sasaki et al., 2006 following genetic analysis, but it is not closely related to Bryde’s whales, lying outside the clade formed by blue, sei and Bryde’s whales (see Fig. 2). Subspecies have been described for several mysticete taxa, but only three are at present commonly in use. They are all blue whales, B. musculus: the Antarctic, sometimes known as the “true,” blue whale, B. m. intermedia; the North Atlantic and North Pacific blue whales (B. m. musculus); and the Southern Hemisphere, mainly
B
Baleen
without the risk of overstimulation. In cetaceans, on the other hand, little neck motility and ineffective head stabilization combined with acrobatic locomotion implies that the semicircular canal system is likely to experience substantially stronger rotatory input (resulting from movements of the entire body) than in terrestrial mammals of similar body size. The small arc size of cetacean canals may therefore reduce the sensitivity to match the high levels of uncompensated rotations, and avoid overstimulation of the canal system. The loss of canal sensitivity, in response to streamlining of the body, is arguably less critical in an aquatic environment than in, for example, an arboreal setting where less accurate sensory clues easily impair locomotor control. Moreover, less effective stabilization of the eyes is not critical in cetacean navigation which is driven by sonar rather than visual clues. Kinematic analyses of cetacean head motion in comparison with terrestrial mammals of similar size will be essential to test the hypothesis that the cetacean canal system experiences stronger rotatory input. Sirenians do show reduced neck motility, but not the extreme semicircular canal reduction of cetaceans. However, they are slow and cautious in their swimming, so that fast and effective head stabilization is not a factor of importance. Their canal size is at the lower end of the non-cetacean mammalian variation, as are terrestrial species that are slow and cautious in their locomotion. Among pinnipeds the semicircular canals of phocids and otariids are different in arc size from terrestrial carnivores, but none show the dramatic size reduction seen in cetaceans. This is expected because they all have motile necks enabling effective head stabilization. Likewise, that phocids have larger canals than terrestrial carnivores is expected, as they are particularly agile in their swimming, and thus follow the normal pattern seen among non-cetacean mammals. However, the smaller anterior and posterior canals of otariids are more difficult to understand. Otariids use a different mode of propulsion than phocids, a bird-like forelimb flight stroke, as opposed to bilateral hind limb undulation, and with a longer neck their center of gravity is located further forward. However, it is not clear how the otariid’s smaller canals with reduced mechanical sensitivity relates to either their locomotor pattern or their body plan.
of a baleen whale. The word derives from the Classical Latin Balaena and ultimately from the Greek Φα´λλαινα [phallaina], “whale.” Baleen plates are suspended from the whale’s palate and are arranged in a row down each side of the mouth, extending from the tip of the rostrum back to the esophageal orifice. The left and right sides are separated by a prominent longitudinal ridge along the midline of the palate. In the rorquals, the two sides are continuous around the tip of the palate, but in the other species the two rows are not confluent. Depending on the species, each “side” of baleen may contain anywhere between 140 and 430 plates. The plates are transversely oriented, and are spaced 1 or 2 cm apart, leaving a narrow gap or slot between adjacent plates. The plates are roughly triangular, with their horizontal basal edges embedded in the palate, their near-vertical labial edges facing outward, and their oblique, fringed lingual edges facing the inside of the mouth. Each plate is slightly curved, with its convex side facing forward, so that its labial edge is directed slightly backward; when the whale is swimming forward,
See Also the Following Article Sense Organs, Overview
References Spoor, F., and Thewissen, J. G. M. (2008). Balance: Comparative and functional anatomy in aquatic mammals. In “Senses on the Threshold” (J. G. M. Thewissen and S. Nummela, eds), Chapter 16. University of California Press, Berkeley, California, USA. Spoor, F., Bajpai, S., Hussain, S. T., Kumar, K., and Thewissen, J. G. M. (2002). Vestibular evidence for the evolution of aquatic behavior in early cetaceans. Nature 417, 163–166. Spoor, F., Garland, Th., Krovitz, G., Ryan, T. M., Silcox, M. T., and Walker, A. (2007). The primate semicircular canal system and locomotion. Proc. Nat. Acad. Sci 104, 10808–10812.
Baleen DALE W. RICE
T
he term baleen (also called whalebone) is a mass noun that refers collectively to the series of thin keratinous plates (“baleen plates,” Fig. 1) that make up the filtering apparatus in the mouth
Figure 1 Parasagittal section through the palate of a sei whale (Balaenoptera borealis), at about midlength of the rostrum, showing the bases of several baleen plates. Anterior is to the right. See Fig. 2 for details.
Baleen
Corium Epithelial layer Pulp
Cornified cortex Cornified medulla
Gum tissue
Figure 2 Magnified section of the specimen in Fig. 1, showing the structure of the roots of the baleen plates. this arrangement helps to direct the flow of water through the interplate gaps from the mouth cavity to the exterior side of the baleen row. The sizes of the plates are smoothly graded, with the longest ones half to two-thirds of the way back from the tip of the rostrum, and only rudimentary ones at the anterior and posterior ends of the row (Williamson, 1973; Pivorunas 1976, 1979). Each baleen plate is made up of a middle layer, the medulla, which is sandwiched between the thin, smooth outer layers, or cortex (Fig. 2). The medulla consists of a mass of fine, hollow, hairlike keratinous tubules which run parallel to the labial side of the plate, and terminate along the lingual side; the tubules are embedded in and cemented together by a horny matrix. Evolutionarily, plates presumably originated by modification of the transverse ridges present on the palates of many terrestrial mammals. In whale fetuses the baleen first appears as a series of crosswise ridges along each side of the palate. The palatal tissue of baleen whales is arranged in three layers. The basal layer, several centimeters thick, is the corium. This is overlain by a thin epithelial layer only a few millimeters thick. The outermost epidermal layer, several centimeters thick, is simply called the gum tissue. The corium gives rise to, and is continuous with, the medulla of each baleen plate, whereas the adjacent epithelial layer is deflected downward to produce the cortical layers of each plate. The dense, rubbery gum tissue does not contribute to the formation of the plates, but simply fills the spaces between their bases, where it provides them a firm support. As each plate grows downward, its cortical layers become cornified sooner than the medulla does. This leaves the first few centimeters of the base of the plate with a layer of soft, highly vascular, corial tissue sandwiched between the keratinous outer layers; this soft layer is often called the pulp, by analogy with the pulp in mammalian teeth (Utrecht, 1965). In life, baleen plates are extremely tough and flexible, but once removed they soon become brittle and are easily fractured. Throughout the life of the whale its baleen plates grow continuously at their base, and wear away along their lingual margin. The cortex and the matrix of the medulla erode away first, freeing the ends of the fibrous tubules for a distance of about 10–20 cm. The freed tubules form a hairy fringe along the entire lingual side of the plate. The fringes of each plate lie back across the lingual edges of the plates
79
immediately behind them, the whole forming a dense hairy mat that covers the internal apertures to the gaps between the plates. This mat effectively filters out the food organisms while allowing the water to flow out of the whale’s mouth through the gaps. Like human fingernails, the thickness of the baleen plates varies with the nutritional state of the whale. Alternating periods of summer gorging and winter fasting leave a regular series of visible growth zones on the surfaces of the plates. These zones have been used to infer the ages of whales, but because of the constant wear, it is rare for more than five or six zones to remain in a plate (Ruud, 1945). A claim that evidence of individual ovulations could be detected in the growth patterns of baleen plates was never confirmed (Utrecht-Cock, 1965). The number of baleen plates per side, and their maximum size, shape, color, and other physical attributes are diagnostic for each species of whale. The right whales (family Balaenidae) with their narrow, highly arched rostrum have 250–390 narrow and extremely long plates, about 0.15–0.25 m. wide and up to 2.50 m. long in the black right whales (Eubalaena spp.) and 4.00 m. in the bowhead whale (B. mysticetus); they are black with a fine whitish fringe. The pygmy right whale (Caperea marginata; family Neobalaenidae) has about 230 narrow, short plates up 0.70-m long and 0.12-m wide; they are white with a black labial margin. The gray whale (Eschrichtius robustus; family Eschrichtiidae) has 140 thick but narrow and short plates, up to 0.10-m wide and 0.50-m long; they are white or ivory in color, with a coarse white fringe that resembles excelsior. The rorquals (family Balaenopteridae) with their wide, flat rostrum, have 270–430 plates with a basal width 50–95% of their length, which varies from about 0.20 m in the small minke whales to 1.00 m in the huge blue whale. Each species of rorqual has a different color-pattern on its baleen plates: humpback (Megaptera novaeangliae)—black with dirty-gray fringe; northern minke (Balaenoptera acutorostrata)—white, sometimes with a narrow black stripe along labial margin; Antarctic minke (B. bonaerensis) and Omura’s (B. omurai)—white with a wide black stripe along labial margin; Bryde’s (B. edeni)—black with light gray fringe; sei (B. borealis)—black with fine, silky, white fringe; fin (B. physalus)—gray and white longitudinal bands, with fringe the same colors; blue (B. musculus)—solid black with black fringe. All of the species of Balaenoptera except the blue whale usually have at least a few all-white baleen plates at the tip of the rostrum, mostly on the right side; this asymmetry is most prominent in the fin whale and Omura’s whale. In the nineteenth century, the long baleen plates of the bowhead and right whales were much in demand for uses where a tough but limber material was needed, so they were the most valuable product of the whale fishery. Landings of whalebone at United States ports reached their highest in 1853, with 5,652,300 pounds worth $1,950,000. The last year that any baleen reached the commercial market was 1930. Much of it was made into umbrella ribs, corset busks, and hoops for skirts. The fibrous fringes were used for brooms and brushes (Stevenson, 1907).
References Pivorunas, A. (1976). A mathematical consideration on the function of baleen plates and their fringes. Sci. Rep. Whales Res. Inst. 28, 37–55. Pivorunas, A. (1979). The feeding mechanisms of baleen whales. Am. Sci. 67, 432–440. Ruud, J. T. (1945). Further studies on the structure of the baleen plates and their application to age determination. Hvalrådets Skrifter 29, 1–69. Stevenson, C. H. (1907). Whalebone: Its production and utilization. Bur. Fish. Doc. 626, 1–12.
B
80
B
Baleen Whales (Mysticetes)
van Utrecht, W. L. (1965). On the growth of the baleen plate of the fin whale and the blue whale. Bijdr. Dierk. 35, 1–38. van Utrecht-Cock, C. N. (1965). Age determination and reproduction of female fin whales, Balaenoptera physalus (Linnaeus, 1758) with special regard to baleen plates and ovaries. Bijdr. Dierk. 35, 39–100. Williamson, G. R. (1973). Counting and measuring baleen and ventral grooves of whales. Sci. Rep. Whales Res. Inst. 25, 279–292.
Baleen Whales (Mysticetes) JOHN L. BANNISTER I. Characteristics and Taxonomy
T
he baleen or whalebone whales (Mysticeti) comprise one of the two recent (non-fossil) cetacean suborders. Modern baleen whales differ from the other suborder (toothed whales, Odontoceti), particularly in their lack of functional teeth. Instead they feed, on relatively very small marine organisms, by means of a highly specialized filter-feeding apparatus made up of baleen plates (“whalebone”) attached to the gum of the upper jaw. Other differences from toothed whales include the baleen whales’ paired blowhole, symmetrical skull, and absence of ribs articulating with the sternum. Baleen whales are generally huge (Fig. 1). In the blue whale, the largest known animal grows to more than 30-m long and weighing more than 170 tons. Like all other cetaceans, baleen whales are totally aquatic, and like most of the toothed whales, they are all marine. Many undertake very long migrations, and some are fast swimming. A few species come close to the coast at some part of their life cycle and may be seen from shore; however, much of their lives is spent far from land in the deep oceans. Baleen whale females grow slightly larger than the males. Animals of the same species tend to be larger in the Southern than in the Northern Hemisphere. Within the mysticetes are four families: (1) right whales (Balaenidae, balaenids); (2) pygmy right whales (Neobalenidae, neobalaenids); (3) gray whales (Eschrichtiidae-eschrichtiids); and (4) “rorquals” (Balaenopteridae, balaenopterids). Within the suborder, 14 species are now generally recognized. Their relationships, including their relationship to terrestrial ungulates, are indicated in Fig. 2. Right whales (Balaenidae) are distinguished from the other three families by their long and narrow baleen plates and arched upper jaw. Other balaenid features include, externally, a disproportionately large head (approximately one-third of the body length), long thin rostrum, and huge bowed lower lips; they lack multiple ventral grooves. Internally, there is no coronoid process on the lower jaw and cervical vertebrae are fused together. Within the family are two distinct groups—the bowhead (Balaena mysticetus) of northern polar waters (formerly known as the “Greenland” right whale), and the three “black” right whales, Eubalaena spp. of more temperate seas, so called to distinguish them from the “Greenland” right whale. All balaenids are robust. Pygmy right whales (Caperea marginata) have some features of both right whales and balaenopterids. The head is short (approximately one quarter of the body length), although with an arched upper jaw and bowed lower lips, and there is a dorsal fin. The relatively long and narrow baleen plates are yellowish white, with a dark outer border, quite different from the all-black balaenid baleen plates. Internally, pygmy right whales have numerous broadened and flattened ribs.
Gray whales (Eschrichtius robustus) are also somewhat intermediate in appearance between right whales and balaenopterids. They have short narrow heads, a slightly arched rostrum, and between two and five deep creases on the throat instead of the balaenopterid ventral grooves. The body is robust. There is no dorsal fin, but a series of 6–12 small “knuckles” along the tail stock. The yellowish-white baleen plates are relatively small. Balaenopterids comprise the seven whales of the genus Balaenoptera (blue, B. musculus; fin, B. physalus; sei, B. borealis; Bryde’s, B. edeni; Omura’s, B. omurai; common minke, B. acutorostrata, Antarctic minke, B. bonaerensis), and the humpback whale (Megaptera novaeangliae). All have relatively short heads, less than a quarter of the body length. In comparison with right whales, the baleen plates are short and wide. Numerous ventral grooves are present, and there is a dorsal fin, sometimes rather small. Internally, the upper jaw is relatively long and unarched, the mandibles are bowed outwards and a coronoid process is present; cervical vertebrae are generally free. All eight balaenopterids are often known as “rorquals” (from the Norse “rørkval, whale with pleats in its throat”). Strictly speaking, the term should probably be applied to the seven Balaenoptera species, recognizing the rather different humpback in its separate genus, but many authors now use it for all eight balaenopterids. Baleen whales are sometimes called “great whales.” Despite their generally huge size, some of the species are relatively small, and it seems preferable to restrict the term to the larger mysticetes (blue, fin, sei, Bryde’s, Omura’s, humpback) together with the largest odontocete (the sperm whale, Physeter macrocephalus). Reviewing the systematics and distribution of the world’s marine mammals, Rice (1998) drew attention to the derivation of the Latin word Mysticeti, and clarified the status of a variant, Mystacoceti. He described the former as coming from Aristotle’s original Greek mustoketos, meaning “the mouse, the whale so-called” or “the mousewhale” (said to be an ironic reference to the animals’ generally vast size). Mystacoceti means “moustache-whales,” and although used occasionally in the past (and more obviously appropriate for whales with baleen in their mouths) has been superseded by Mysticeti. Within the suborder, 14 species are now generally recognized. Although Rice believed that all right whales belong with the bowhead in the genus Balaena, recent genetic analyses have recognized three separate right whale species, in the genus Eubalaena: in the North Atlantic (E. glacialis); in the North Pacific (E. japonica); and in the Southern Hemisphere (E. australis). Indeed, Eubalaena is the only mysticete genus where separate species are recognized in each hemisphere. The taxonomic status of Bryde’s whales is confused. Currently one species is recognized (B. edeni) but it has several forms, at least one of which may be a separate species. The “ordinary” form has two distinct sub-forms—offshore and inshore. Another animal, B. brydei, was described from specimens taken off South Africa, but subsequently accepted as the same species as B. edeni. The situation has not been helped because the location of the type specimen of edeni was uncertain until recently and its genetic make-up has yet to be determined. A further similar but smaller species, Omura’s whale, B. omurai, was described in 2003, and recently accepted (Sasaki et al., 2006 following genetic analysis, but it is not closely related to Bryde’s whales, lying outside the clade formed by blue, sei and Bryde’s whales (see Fig. 2). Subspecies have been described for several mysticete taxa, but only three are at present commonly in use. They are all blue whales, B. musculus: the Antarctic, sometimes known as the “true,” blue whale, B. m. intermedia; the North Atlantic and North Pacific blue whales (B. m. musculus); and the Southern Hemisphere, mainly