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Jaakkola, K., Fellner, W., Erb, L., Rodriguez, M., and Guarino, E. (2005). Understanding of the concept of numerically “less” by bottlenose dolphins (Tursiops truncatus). J. Comp. Psychol. 119, 296–303. Janik, V.M. (2000). Whistle matching in wild bottlenose dolphins (Tursiops truncatus). Science 289, 1357–1360. Janik, V.M. (1999). Pitfalls in the classification of behaviour: A comparison of dolphin whistle classification methods. Anim. Behav. 57, 133–143. Janik, V.M., and Sayigh, L.S. (2013). Communication in bottlenose dolphins: 50 years of signature whistle research. J. Comp. Physiol. A 199, 479–489. Kilian, A., Yaman, S., Von Fersen, L., and Gunturkun, O. (2003). A bottlenose dolphin discriminates visual stimuli differing in numerosity. Learn. Behav. 31, 133–142. Lieberman, P. (1984). The Biology and Evolution of Language. Harvard University Press, Cambridge. Lilly, J.C. (1961). Man and Dolphin. Doubleday, New York, NY. Lilly, J.C. (1967). The Mind of the Dolphin: A Nonhuman Intelligence. Doubleday, New York, NY. Mercado III, E.M., Killebrew, D.A., Pack, A.A., Macha, I.V.B., and Herman, L.M. (2000). Generalization of same-different classification abilities in bottlenosed dolphins. Behav. Process. 50, 79–94. Pack, A.A., and Herman, L.M. (1995). Sensory integration in the bottlenosed dolphin: Immediate recognition of complex shapes across the senses of echolocation and vision. J. Acoust. Soc. Amer. 98, 722–733. Pack, A.A., and Herman, L.M. (2006). Dolphin social cognition and joint attention: Our current understanding. Aquat. Mamm. 32, 443–460. Pack, A.A., and Herman, L.M. (2007). The dolphin’s (Tursiops truncatus) understanding of human gaze and pointing: Knowing what and where. J. Comp. Psychol. 121, 34–45. Pryor, K., Haag, R., and O’Reilly, J. (1969). The creative porpoise: Training for novel behavior. J. Exp. Anal. Behav. 12, 653–661. Richards, D.G., Wolz, J.P., and Herman, L.M. (1984). Vocal mimicry of computer generated sounds and vocal labeling of objects by a bottlenose dolphin, Tursiops truncatus. J. Comp. Psychol. 98, 10–28. Reiss, D., and Marino, L. (2001). Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence. Proc. Nat. Acad. Sci. 98, 5937–5942. Rendell, L., and Whitehead, H. (2001). Culture in whales and dolphins. Behav. Brain Sci. 24, 309–382. Savage-Rumbaugh, E.S. (1986). Ape Language: From Conditioned Response to Symbol. Columbia University Press, New York, NY. Savage-Rumbaugh, E.S., Murphy, J., Sevcik, R.A., Brakke, K.E., Williams, S.L., and Rumbaugh, D.M. (1993). Language comprehension in ape and child. Monogr. Soc. Res. Child Dev. 58, 256. Smith, J.D., Schull, J., Strote, J., McGee, K., Egnor, R., and Erb, L. (1995). The uncertain response in the bottlenose dolphin (Tursiops truncatus). J. Exp. Psychol. Gen. 124, 391–408. Smolker, R., Richards, A., Connor, R., Mann, J., and Berggren, P. (1997). Sponge carrying by dolphins (Delphinidae, Tursiops sp.): A foraging specialization involving tool use? Ethology 103, 454–465. Thompson, R.K.R., and Herman, L.M. (1977). Memory for lists of sounds by the bottlenosed dolphin: Convergence of memory processes with humans? Science 195, 501–503. Tomasello, M., and Call, J. (1997). Primate Cognition. Oxford University Press, New York, NY. Tyack, P.L. (1986). Whistle repertoires of two bottlenose dolphins, Tursiops truncatus: Mimicry of signature whistles? Behav. Ecol. Sociobiol. 18, 251–257. Wood, F.G. (1973). Marine Mammals and Man: The Navy’s Porpoises and Sea Lions. Luce, Washington, DC. Wilson, E.O. (1975). Sociobiology. Belknap, Cambridge. Xitco Jr., M.J., Gory, J.D., and Kuczaj, I.I. (2001). Spontaneous pointing by bottlenose dolphins (Tursiops truncatus). Anim. Cogn 4, 115–123.
LEOPARD SEAL Hydrurga leptonyx Tracey Rogers The leopard seal, Hydrurga leptonyx, is the largest Antarctic pack ice seal. It is a predator of penguins, other marine mammals and zooplankton. This is a unique dietary combination for mammals.
I. Characteristics and Taxonomy Female leopard seals grow up to 3.8 m in length and weigh up to 500 kg, and males grow up to 3.3 m in length and weigh up to 300 kg (Rogers, 2009). They have an elongated, streamlined body with long, flipper-like forelimbs (Fig. 1). Claws on the first digit of the foreflipper are set back from the free edge, a trait common in otariids, but only found in Ross seals and leopard seals among the phocid seals (Rogers, 2009). Leopard seals have large, reptilian-shaped heads and a very large mouth. They are gray in color with irregular, darker spots. Pups are approximately 120 cm long at birth. The leopard seal is the only member of the genus Hydrurga (Order Carnivora; Family Phocidae). It is one of the Antarctic true seals in the tribe Lobodontini.
II. Distribution and Abundance Leopard seals are solitary, and widely dispersed at low densities throughout the circumpolar Antarctic pack ice (Fig. 2; Rogers et al., 2013). When the sea ice extent is minimal, leopard seals are restricted to coastal habitats (Meade et al., 2015). While the majority of the leopard seal population remains within the pack ice (Rogers et al., 2013), seals are regular, although not abundant, winter visitors north to the subantarctic and along the southern continents. Leopard seals further north, in mid-latitude regions, tend to be younger animals in poor health, as indicated by elevated serum protein fractions and poor body condition (Gray et al., 2005). The leopard seal population is estimated to be 222,000–440,000, but this may be negatively biased (Southwell et al., 2008).
III. Ecology Leopard seals are an important component of the Antarctic pack ice ecosystem. They are widespread and consume prey at a range of trophic levels. The leopard seal is unusual as a mammalian predator; acting as both an apex predator and a planktivore (Rogers, 2009). Marine mammals typically consume prey that is small relative to their body size. However, the leopard seal takes large-bodied prey including crabeater (Lobodon carcinophaga), Weddell (Leptonychotes weddellii) and southern elephant seals (Mirounga iconina) (HallAspland and Rogers, 2007), fur seals (Arctocehalus spp.) (Krause et al., 2015), and penguins (Rogers and Bryden, 1995). The leopard seal is responsible for more predation on large, warm-blooded prey than any other pinniped (Rogers, 2009). Compared to other pinnipeds they have an extended food transit time, which is more similar to terrestrial carnivores (Hall-Aspland et al., 2011). Their dentition is proposed to have dual-specialization; to capture and kill large prey, the canines and incisors are used in raptorial “grip-and-tear” feeding style (Rogers, 2009) and yet to feed upon small prey, such as Euphausids, tightly occluding, tricusped postcanines are used as a sieve, along with suction. The gut microbiota of leopard seals, which is important for digestion, is typical of Arctic and Antarctic phocids,
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Figure 1 Leopard seal, Hydrurga leptonyx (Illustration by Pieter Folkens).
L Figure 3 Male leopard seal H. leptonyx singing underwater (Photo by Tracey Rogers).
Figure 2 Leopard seal distribution. Map produced by Anders Skoglund, Norwegian Polar Institute. with the exception of the abundance of bacterial species found in their prey, including Antarctic penguins and krill (Nelson et al., 2013).
IV. Behavior and Physiology The acoustic behavior of the leopard seal is believed to be linked primarily to their breeding behavior (Rogers, 2009). Captive female leopard seals produce “solicitation calls,” meaning that they vocalize underwater when they have elevated plasma estradiol levels, presumably to advertise sexual fertility. Male seals also vocalize underwater coinciding with the timing of the breeding season, which falls between November and the first week of January (Fig. 3; Rogers et al., 2013). Male seals produce vocalizations in distinctive patterns; each male has a unique “song” (Rogers and Cato, 2002). Young male leopard seals produce an array of call types, whereas adult seals produce fewer, and more stylized calls (Rogers, 2007). Older, larger seals produce vocal signals at a higher pitch than younger seals
(Rogers, 2007). The underwater vocalizations of the leopard seal are loud, and can be up to 177 dB re 1 μPa at 1 m (Rogers, 2014). Leopard seals are very modest divers, they perform short (~2 min), shallow (30 m or less) dives (Krause et al., 2015). Compared to other marine mammals, they have a small spleen, low hemoglobin concentration, and low packed cell volume (Gray et al., 2006). This results in a lower whole body oxygen carrying capacity, reflecting their limited diving capacity. Leopard seals rely on sea ice for breeding, molting, and as a resting platform. Although the sea ice on which the seals haulout drifts, the seals remain within a restricted home range (Meade et al., 2015). Older seals have greater spatial separation than younger seals; younger seals are found in higher population densities (Rogers et al., 2013). Leopard seals have low levels of bioaccumulated heavy metals relative to Arctic seals. They have high cortisol (stress hormone) levels for a mammal, which may be a result of living in extreme Antarctic weather conditions (Hogg and Rogers, 2009).
V. Life History Male leopard seals reach sexually maturity by 4.5 years, and females by 4 years of age. Females come into estrus asynchronously with the mating season extending across December and January. Mating occurs in the water, although it has been observed only for captive seals. Male
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and female seals vocalize underwater and encircle one another in a stylized underwater display prior to mounting. Births occur from October to mid-November. Females give birth to their pups and wean them on floes of Antarctic pack ice. Males do not remain with the females; hence, only mother-pup pairs are observed on the ice surface. Lactation lasts for approximately 4 weeks (Rogers, 2009).
VI. Interactions With Humans Leopard seals have never been commercially harvested because of their dispersed distribution. Scientists working in Antarctica as well as tourists diving off the western Antarctic Peninsula have had predominantly benign interactions with leopard seals, although there has been one reported human fatality. Predicted decreases in Antarctic sea ice due to climate change are likely to negatively affect the leopard seal.
See Also the Following Articles Antarctic Marine Mammals Predation
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Earless Seals (Phocidae)
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Pinnipeds
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Gray, R., Canfield, P., and Rogers, T. (2005). Serum proteins in the leopard seal, Hydrurga leptonyx, in Prydz Bay, Eastern Antarctica and the coast of NSW, Australia. Comp. Biochem. Physiol. B 142, 67–78. Gray, R., Canfield, P., and Rogers, T. (2006). Histology of selected tissues of the leopard seal and implications for functional adaptations to an aquatic lifestyle. J. Anat. 209, 179–199. Hall-Aspland, S., and Rogers, T. (2007). Identification of hairs found in leopard seal (Hydrurga leptonyx) scats. Polar Biol. 30, 581–585. Hall-Aspland, S., Rogers, T., Canfield, R., and Tripovich, J. (2011). Food transit times in captive leopard seals (Hydrurga leptonyx). Polar Biol. 34, 95–99. Hogg, C.J., and Rogers, T.L. (2009). Measuring stress in Antarctic seals. In Health of Antarctic Wildlife, pp. 263–270. Springer, Berlin, Heidelberg. Krause, D.J., Goebel, M.E., Marshall, G.J., and Abernathy, K. (2015). Novel foraging strategies observed in a growing leopard seal (Hydrurga leptonyx) population at Livingston Island, Antarctic Peninsula. Anim. Biotelem. 3, 24. Meade, J., Ciaglia, M.B., Slip, D.J., Negrete, J., Márquez, M.E.I., Mennucci, J., et al. (2015). Spatial patterns in activity of leopard seals Hydrurga leptonyx in relation to sea ice. Mar. Ecol. Prog. Ser. 521, 265–275. Nelson, T.M., Rogers, T.L., Carlini, A.R., and Brown, M.V. (2013). Diet and phylogeny shape the gut microbiota of Antarctic seals: a comparison of wild and captive animals. Env. Micro. 15, 1132–1145. Rogers, T.L. (2007). Age-related differences in the acoustic characteristics of male leopard seals. Hydrurga leptonyx. J. Acoust. Soc. Amer. 122, 596–605. Rogers, T.L. (2009). Leopard seal Hydrurga leptonyx. In “Encyclopedia of Marine Mammals”, (W.F. Perrin, B. Wursig, and J.G.M. Thewissen, Eds), pp. 673–674. Academic Press, San Diego. Rogers, T.L. (2014). Source levels of the underwater calls of a male leopard seal. J. Acoust. Soc. Amer. 136, 1495–1498. Rogers, T., and Bryden, M.M. (1995). Predation of Adélie penguins (Pygoscelis adeliae) by leopard seals (Hydrurga leptonyx) in Prydz Bay, Antarctica. Can. J. Zool. 73, 1001–1004. Rogers, T.L., and Cato, D.H. (2002). Individual variation in the acoustical behaviour of the adult male leopard seal, Hydrurga leptonyx. Behaviour. 139, 1267–1286. Rogers, T.L., Ciaglia, M.B., Klinck, H., and Southwell, C. (2013). Density can be misleading for low-density species: benefits of passive acoustic monitoring. PLoS One 8, e52542. Southwell, C., Paxton, C.G., Borchers, D., Boveng, P., Rogers, T., and William, K. (2008). Uncommon or cryptic? Challenges in estimating leopard seal abundance by conventional but state-of-the-art methods. Deep Sea Res. 55, 519–531.
LOCOMOTION, TERRESTRIAL Frank E. Fish I. Terrestrial Locomotion Evolution Although swimming is typically associated with marine mammals, various species are amphibious and capable of terrestrial locomotion. Pinnipeds spend a considerable amount of time on land, where they rest, molt, copulate, and pup. Sea otters and polar bears have gaits (i.e., regularly repeating sequence of limb movements) more similar to terrestrial mammals. Despite locomotor specializations for an aquatic existence, all marine mammals had terrestrial ancestors (Thewissen and Fish, 1997; Domning, 2000). Stem cetaceans of the Pakicetidae had gracile limbs and probably moved on land with gaits similar to modern terrestrial mammals. More aquatic quadrupedal cetaceans (Ambulocetus), pinnipeds (Enaliarctos), and sirenians (Pezosiren) likely modified their terrestrial gaits to compensate for morphological changes required for swimming. The evolution from a terrestrial to a fully aquatic existence required changes to the body and limbs that placed constraints to effectively move on land. In being both semiaquatic and semiterrestrial, transitional states of marine mammals faced an “energetic hurdle” (Williams, 1999). Acquiring the adaptations necessary to become an aquatic specialist meant that movement on land requires a higher cost of transport than for swimming (Fish, 2000). Terrestrial locomotion of marine mammals is characterized by low speeds and low stamina (Backhouse, 1961).
II. Carnivore Terrestrial Locomotion Polar bears move with terrestrial gaits of slow-to-fast walks, slow runs and a pace (Renous et al., 1998). Polar bears can move at 4 km/hr and cover 14–18 km/day (Derocher, 2012). Bears move at faster gaits with shorter foot contact times on snow than on ice. The walking gait of the polar bear is inefficient with twice the energy consumption of more terrestrial mammals (Hurst et al., 1982). Faster movement is achieved with a gallop with a short-gathered suspension phase where the bear’s feet are not in contact with the ground (Renous et al., 1998). The stance of polar bears is plantigrade with the entire foot contacting the ground. The large pads on the bottom of the foot with the long hairs along the margins of the pads produce a snowshoe-like surface. In walking, 3 feet are always in contact with the ground forming a stable triangle of support. The gallop is a stable gait for fast locomotion, where the sequence of the feet contacting the ground provides a wide stance. Stability on ice can also be provided in a novel bipedal gait in which the hindfeet propel the body as the forefeet slide on the ice (Renous et al., 1998). Walking by sea otters is restricted by the relatively short forelimbs and webbed hindfeet with an elongate outer fifth digit. Walking by the sea otter is characterized by raising only one foot off the ground at any time with the back highly arched (Tarasoff et al., 1972). The walk has been described as a rolling gait as the feet step laterally. The only other gait is a half bound, which is used for fast travel. In a half bound, the hindfeet contact the ground in unison, but the forefeet do not contact the ground simultaneously. This gait differs from the bound where each pair of feet moves simultaneously. The gaits of sea otters are similar to the related river otter (Lontra canadensis), but the sea otter appears more awkward and less efficient than the river otter (Tarasoff et al., 1972).
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Jaakkola, K., Fellner, W., Erb, L., Rodriguez, M., and Guarino, E. (2005). Understanding of the concept of numerically “less” by bottlenose dolphins (Tursiops truncatus). J. Comp. Psychol. 119, 296–303. Janik, V.M. (2000). Whistle matching in wild bottlenose dolphins (Tursiops truncatus). Science 289, 1357–1360. Janik, V.M. (1999). Pitfalls in the classification of behaviour: A comparison of dolphin whistle classification methods. Anim. Behav. 57, 133–143. Janik, V.M., and Sayigh, L.S. (2013). Communication in bottlenose dolphins: 50 years of signature whistle research. J. Comp. Physiol. A 199, 479–489. Kilian, A., Yaman, S., Von Fersen, L., and Gunturkun, O. (2003). A bottlenose dolphin discriminates visual stimuli differing in numerosity. Learn. Behav. 31, 133–142. Lieberman, P. (1984). The Biology and Evolution of Language. Harvard University Press, Cambridge. Lilly, J.C. (1961). Man and Dolphin. Doubleday, New York, NY. Lilly, J.C. (1967). The Mind of the Dolphin: A Nonhuman Intelligence. Doubleday, New York, NY. Mercado III, E.M., Killebrew, D.A., Pack, A.A., Macha, I.V.B., and Herman, L.M. (2000). Generalization of same-different classification abilities in bottlenosed dolphins. Behav. Process. 50, 79–94. Pack, A.A., and Herman, L.M. (1995). Sensory integration in the bottlenosed dolphin: Immediate recognition of complex shapes across the senses of echolocation and vision. J. Acoust. Soc. Amer. 98, 722–733. Pack, A.A., and Herman, L.M. (2006). Dolphin social cognition and joint attention: Our current understanding. Aquat. Mamm. 32, 443–460. Pack, A.A., and Herman, L.M. (2007). The dolphin’s (Tursiops truncatus) understanding of human gaze and pointing: Knowing what and where. J. Comp. Psychol. 121, 34–45. Pryor, K., Haag, R., and O’Reilly, J. (1969). The creative porpoise: Training for novel behavior. J. Exp. Anal. Behav. 12, 653–661. Richards, D.G., Wolz, J.P., and Herman, L.M. (1984). Vocal mimicry of computer generated sounds and vocal labeling of objects by a bottlenose dolphin, Tursiops truncatus. J. Comp. Psychol. 98, 10–28. Reiss, D., and Marino, L. (2001). Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence. Proc. Nat. Acad. Sci. 98, 5937–5942. Rendell, L., and Whitehead, H. (2001). Culture in whales and dolphins. Behav. Brain Sci. 24, 309–382. Savage-Rumbaugh, E.S. (1986). Ape Language: From Conditioned Response to Symbol. Columbia University Press, New York, NY. Savage-Rumbaugh, E.S., Murphy, J., Sevcik, R.A., Brakke, K.E., Williams, S.L., and Rumbaugh, D.M. (1993). Language comprehension in ape and child. Monogr. Soc. Res. Child Dev. 58, 256. Smith, J.D., Schull, J., Strote, J., McGee, K., Egnor, R., and Erb, L. (1995). The uncertain response in the bottlenose dolphin (Tursiops truncatus). J. Exp. Psychol. Gen. 124, 391–408. Smolker, R., Richards, A., Connor, R., Mann, J., and Berggren, P. (1997). Sponge carrying by dolphins (Delphinidae, Tursiops sp.): A foraging specialization involving tool use? Ethology 103, 454–465. Thompson, R.K.R., and Herman, L.M. (1977). Memory for lists of sounds by the bottlenosed dolphin: Convergence of memory processes with humans? Science 195, 501–503. Tomasello, M., and Call, J. (1997). Primate Cognition. Oxford University Press, New York, NY. Tyack, P.L. (1986). Whistle repertoires of two bottlenose dolphins, Tursiops truncatus: Mimicry of signature whistles? Behav. Ecol. Sociobiol. 18, 251–257. Wood, F.G. (1973). Marine Mammals and Man: The Navy’s Porpoises and Sea Lions. Luce, Washington, DC. Wilson, E.O. (1975). Sociobiology. Belknap, Cambridge. Xitco Jr., M.J., Gory, J.D., and Kuczaj, I.I. (2001). Spontaneous pointing by bottlenose dolphins (Tursiops truncatus). Anim. Cogn 4, 115–123.
LEOPARD SEAL Hydrurga leptonyx Tracey Rogers The leopard seal, Hydrurga leptonyx, is the largest Antarctic pack ice seal. It is a predator of penguins, other marine mammals and zooplankton. This is a unique dietary combination for mammals.
I. Characteristics and Taxonomy Female leopard seals grow up to 3.8 m in length and weigh up to 500 kg, and males grow up to 3.3 m in length and weigh up to 300 kg (Rogers, 2009). They have an elongated, streamlined body with long, flipper-like forelimbs (Fig. 1). Claws on the first digit of the foreflipper are set back from the free edge, a trait common in otariids, but only found in Ross seals and leopard seals among the phocid seals (Rogers, 2009). Leopard seals have large, reptilian-shaped heads and a very large mouth. They are gray in color with irregular, darker spots. Pups are approximately 120 cm long at birth. The leopard seal is the only member of the genus Hydrurga (Order Carnivora; Family Phocidae). It is one of the Antarctic true seals in the tribe Lobodontini.
II. Distribution and Abundance Leopard seals are solitary, and widely dispersed at low densities throughout the circumpolar Antarctic pack ice (Fig. 2; Rogers et al., 2013). When the sea ice extent is minimal, leopard seals are restricted to coastal habitats (Meade et al., 2015). While the majority of the leopard seal population remains within the pack ice (Rogers et al., 2013), seals are regular, although not abundant, winter visitors north to the subantarctic and along the southern continents. Leopard seals further north, in mid-latitude regions, tend to be younger animals in poor health, as indicated by elevated serum protein fractions and poor body condition (Gray et al., 2005). The leopard seal population is estimated to be 222,000–440,000, but this may be negatively biased (Southwell et al., 2008).
III. Ecology Leopard seals are an important component of the Antarctic pack ice ecosystem. They are widespread and consume prey at a range of trophic levels. The leopard seal is unusual as a mammalian predator; acting as both an apex predator and a planktivore (Rogers, 2009). Marine mammals typically consume prey that is small relative to their body size. However, the leopard seal takes large-bodied prey including crabeater (Lobodon carcinophaga), Weddell (Leptonychotes weddellii) and southern elephant seals (Mirounga iconina) (HallAspland and Rogers, 2007), fur seals (Arctocehalus spp.) (Krause et al., 2015), and penguins (Rogers and Bryden, 1995). The leopard seal is responsible for more predation on large, warm-blooded prey than any other pinniped (Rogers, 2009). Compared to other pinnipeds they have an extended food transit time, which is more similar to terrestrial carnivores (Hall-Aspland et al., 2011). Their dentition is proposed to have dual-specialization; to capture and kill large prey, the canines and incisors are used in raptorial “grip-and-tear” feeding style (Rogers, 2009) and yet to feed upon small prey, such as Euphausids, tightly occluding, tricusped postcanines are used as a sieve, along with suction. The gut microbiota of leopard seals, which is important for digestion, is typical of Arctic and Antarctic phocids,
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Figure 1 Leopard seal, Hydrurga leptonyx (Illustration by Pieter Folkens).
L Figure 3 Male leopard seal H. leptonyx singing underwater (Photo by Tracey Rogers).
Figure 2 Leopard seal distribution. Map produced by Anders Skoglund, Norwegian Polar Institute. with the exception of the abundance of bacterial species found in their prey, including Antarctic penguins and krill (Nelson et al., 2013).
IV. Behavior and Physiology The acoustic behavior of the leopard seal is believed to be linked primarily to their breeding behavior (Rogers, 2009). Captive female leopard seals produce “solicitation calls,” meaning that they vocalize underwater when they have elevated plasma estradiol levels, presumably to advertise sexual fertility. Male seals also vocalize underwater coinciding with the timing of the breeding season, which falls between November and the first week of January (Fig. 3; Rogers et al., 2013). Male seals produce vocalizations in distinctive patterns; each male has a unique “song” (Rogers and Cato, 2002). Young male leopard seals produce an array of call types, whereas adult seals produce fewer, and more stylized calls (Rogers, 2007). Older, larger seals produce vocal signals at a higher pitch than younger seals
(Rogers, 2007). The underwater vocalizations of the leopard seal are loud, and can be up to 177 dB re 1 μPa at 1 m (Rogers, 2014). Leopard seals are very modest divers, they perform short (~2 min), shallow (30 m or less) dives (Krause et al., 2015). Compared to other marine mammals, they have a small spleen, low hemoglobin concentration, and low packed cell volume (Gray et al., 2006). This results in a lower whole body oxygen carrying capacity, reflecting their limited diving capacity. Leopard seals rely on sea ice for breeding, molting, and as a resting platform. Although the sea ice on which the seals haulout drifts, the seals remain within a restricted home range (Meade et al., 2015). Older seals have greater spatial separation than younger seals; younger seals are found in higher population densities (Rogers et al., 2013). Leopard seals have low levels of bioaccumulated heavy metals relative to Arctic seals. They have high cortisol (stress hormone) levels for a mammal, which may be a result of living in extreme Antarctic weather conditions (Hogg and Rogers, 2009).
V. Life History Male leopard seals reach sexually maturity by 4.5 years, and females by 4 years of age. Females come into estrus asynchronously with the mating season extending across December and January. Mating occurs in the water, although it has been observed only for captive seals. Male
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552
and female seals vocalize underwater and encircle one another in a stylized underwater display prior to mounting. Births occur from October to mid-November. Females give birth to their pups and wean them on floes of Antarctic pack ice. Males do not remain with the females; hence, only mother-pup pairs are observed on the ice surface. Lactation lasts for approximately 4 weeks (Rogers, 2009).
VI. Interactions With Humans Leopard seals have never been commercially harvested because of their dispersed distribution. Scientists working in Antarctica as well as tourists diving off the western Antarctic Peninsula have had predominantly benign interactions with leopard seals, although there has been one reported human fatality. Predicted decreases in Antarctic sea ice due to climate change are likely to negatively affect the leopard seal.
See Also the Following Articles Antarctic Marine Mammals Predation
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Earless Seals (Phocidae)
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Pinnipeds
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References
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Gray, R., Canfield, P., and Rogers, T. (2005). Serum proteins in the leopard seal, Hydrurga leptonyx, in Prydz Bay, Eastern Antarctica and the coast of NSW, Australia. Comp. Biochem. Physiol. B 142, 67–78. Gray, R., Canfield, P., and Rogers, T. (2006). Histology of selected tissues of the leopard seal and implications for functional adaptations to an aquatic lifestyle. J. Anat. 209, 179–199. Hall-Aspland, S., and Rogers, T. (2007). Identification of hairs found in leopard seal (Hydrurga leptonyx) scats. Polar Biol. 30, 581–585. Hall-Aspland, S., Rogers, T., Canfield, R., and Tripovich, J. (2011). Food transit times in captive leopard seals (Hydrurga leptonyx). Polar Biol. 34, 95–99. Hogg, C.J., and Rogers, T.L. (2009). Measuring stress in Antarctic seals. In Health of Antarctic Wildlife, pp. 263–270. Springer, Berlin, Heidelberg. Krause, D.J., Goebel, M.E., Marshall, G.J., and Abernathy, K. (2015). Novel foraging strategies observed in a growing leopard seal (Hydrurga leptonyx) population at Livingston Island, Antarctic Peninsula. Anim. Biotelem. 3, 24. Meade, J., Ciaglia, M.B., Slip, D.J., Negrete, J., Márquez, M.E.I., Mennucci, J., et al. (2015). Spatial patterns in activity of leopard seals Hydrurga leptonyx in relation to sea ice. Mar. Ecol. Prog. Ser. 521, 265–275. Nelson, T.M., Rogers, T.L., Carlini, A.R., and Brown, M.V. (2013). Diet and phylogeny shape the gut microbiota of Antarctic seals: a comparison of wild and captive animals. Env. Micro. 15, 1132–1145. Rogers, T.L. (2007). Age-related differences in the acoustic characteristics of male leopard seals. Hydrurga leptonyx. J. Acoust. Soc. Amer. 122, 596–605. Rogers, T.L. (2009). Leopard seal Hydrurga leptonyx. In “Encyclopedia of Marine Mammals”, (W.F. Perrin, B. Wursig, and J.G.M. Thewissen, Eds), pp. 673–674. Academic Press, San Diego. Rogers, T.L. (2014). Source levels of the underwater calls of a male leopard seal. J. Acoust. Soc. Amer. 136, 1495–1498. Rogers, T., and Bryden, M.M. (1995). Predation of Adélie penguins (Pygoscelis adeliae) by leopard seals (Hydrurga leptonyx) in Prydz Bay, Antarctica. Can. J. Zool. 73, 1001–1004. Rogers, T.L., and Cato, D.H. (2002). Individual variation in the acoustical behaviour of the adult male leopard seal, Hydrurga leptonyx. Behaviour. 139, 1267–1286. Rogers, T.L., Ciaglia, M.B., Klinck, H., and Southwell, C. (2013). Density can be misleading for low-density species: benefits of passive acoustic monitoring. PLoS One 8, e52542. Southwell, C., Paxton, C.G., Borchers, D., Boveng, P., Rogers, T., and William, K. (2008). Uncommon or cryptic? Challenges in estimating leopard seal abundance by conventional but state-of-the-art methods. Deep Sea Res. 55, 519–531.
LOCOMOTION, TERRESTRIAL Frank E. Fish I. Terrestrial Locomotion Evolution Although swimming is typically associated with marine mammals, various species are amphibious and capable of terrestrial locomotion. Pinnipeds spend a considerable amount of time on land, where they rest, molt, copulate, and pup. Sea otters and polar bears have gaits (i.e., regularly repeating sequence of limb movements) more similar to terrestrial mammals. Despite locomotor specializations for an aquatic existence, all marine mammals had terrestrial ancestors (Thewissen and Fish, 1997; Domning, 2000). Stem cetaceans of the Pakicetidae had gracile limbs and probably moved on land with gaits similar to modern terrestrial mammals. More aquatic quadrupedal cetaceans (Ambulocetus), pinnipeds (Enaliarctos), and sirenians (Pezosiren) likely modified their terrestrial gaits to compensate for morphological changes required for swimming. The evolution from a terrestrial to a fully aquatic existence required changes to the body and limbs that placed constraints to effectively move on land. In being both semiaquatic and semiterrestrial, transitional states of marine mammals faced an “energetic hurdle” (Williams, 1999). Acquiring the adaptations necessary to become an aquatic specialist meant that movement on land requires a higher cost of transport than for swimming (Fish, 2000). Terrestrial locomotion of marine mammals is characterized by low speeds and low stamina (Backhouse, 1961).
II. Carnivore Terrestrial Locomotion Polar bears move with terrestrial gaits of slow-to-fast walks, slow runs and a pace (Renous et al., 1998). Polar bears can move at 4 km/hr and cover 14–18 km/day (Derocher, 2012). Bears move at faster gaits with shorter foot contact times on snow than on ice. The walking gait of the polar bear is inefficient with twice the energy consumption of more terrestrial mammals (Hurst et al., 1982). Faster movement is achieved with a gallop with a short-gathered suspension phase where the bear’s feet are not in contact with the ground (Renous et al., 1998). The stance of polar bears is plantigrade with the entire foot contacting the ground. The large pads on the bottom of the foot with the long hairs along the margins of the pads produce a snowshoe-like surface. In walking, 3 feet are always in contact with the ground forming a stable triangle of support. The gallop is a stable gait for fast locomotion, where the sequence of the feet contacting the ground provides a wide stance. Stability on ice can also be provided in a novel bipedal gait in which the hindfeet propel the body as the forefeet slide on the ice (Renous et al., 1998). Walking by sea otters is restricted by the relatively short forelimbs and webbed hindfeet with an elongate outer fifth digit. Walking by the sea otter is characterized by raising only one foot off the ground at any time with the back highly arched (Tarasoff et al., 1972). The walk has been described as a rolling gait as the feet step laterally. The only other gait is a half bound, which is used for fast travel. In a half bound, the hindfeet contact the ground in unison, but the forefeet do not contact the ground simultaneously. This gait differs from the bound where each pair of feet moves simultaneously. The gaits of sea otters are similar to the related river otter (Lontra canadensis), but the sea otter appears more awkward and less efficient than the river otter (Tarasoff et al., 1972).