Thebearded seal (Erignathus barbatus), also called thesquare flipper seal, is a medium-sizedpinniped that is found in and near to theArctic Ocean.[3] It gets itsgeneric name from twoGreek words (eri andgnathos) that refer to its heavy jaw. The other part of itsLinnaean name means bearded and refers to its most characteristic feature, the conspicuous and very abundant whiskers. When dry, these whiskers curl very elegantly,[3] giving the bearded seal a "raffish" look.[citation needed]
Bearded seals are the largest northern phocid. They have been found to weigh as much as 300 kg (660 lb) with the females being the largest. However, male and female bearded seals are not verydimorphic.[3]
The only member of the genusErignathus, the bearded seal is unique in that it is an intermediate. Bearded seals belong to the familyPhocidae which contains two subfamilies:Phocinae andMonachinae. The bearded seal possesses characteristics of both of these subfamilies.[3]
Fossils first described in 2002 indicate that, during thePleistocene epoch, bearded seals ranged as far south asSouth Carolina.[4]
Distinguishing features of thisearless seal include square fore flippers and thick bristles on its muzzle. Adults are greyish-brown in colour, darker on the back; rarely with a few faint spots on the back or dark spots on the sides. Occasionally the face and neck are reddish brown. Bearded seal pups are born with a greyish-brown natal fur with scattered patches of white on the back and head. The bearded seal is unique in the subfamilyPhocinae in having two pairs ofteats, a feature it shares withmonk seals.
Bearded seals reach about 2.1 to 2.7 m (6.9 to 8.9 ft) in nose-to-tail length and from 200 to 430 kg (441 to 948 lb) in weight.[5] The female seal is larger than the male, meaning that they aresexually dimorphic.
Bearded seals, along withringed seals, are a major food source forpolar bears.[6] They are also an important food source for theInuit of theArctic coast. TheInuit language name for the seal isugjuk[7][8] (plural:ugjuit) oroogrook oroogruk. The Inuit preferred theringed seal for food and light; the meat would be eaten and theblubber burnt in thekudlik (stone lamp). The skin of the bearded seal is tougher than regular seal and was used to make shoes, whips,dog sled harnesses, to cover a wooden frame boat, theUmiak and in constructing summer tents known astupiq.[9]
The body fat content of a bearded seal is about 25–40%.[10]
Although the range typically only extends down into subarctic areas bearded seals have been seen in Japan and China as well as extremely far south of their range in Germany, Netherlands, United Kingdom, France, Spain and Portugal.[2]
Primarilybenthic, bearded seals feed on a variety of small prey found along the ocean floor, includingclams,squid,crustaceans, andfish.[5] Their whiskers serve as feelers[15] in the soft bottom sediments. Adults tend not to dive very deep, favoring shallow coastal areas no more than 300 m (980 ft) deep. Pups up to one year old, however, will venture much deeper, diving as deep as 450 m (1,480 ft). In a study conducted during the summer months, the seals have been found to feed on invertebrates such asanemones,sea cucumbers, andpolychaete worms.[13] The same study found that flatfishes (such asAmerican plaice), sculpins, andArctic cod made up most of their summer diet.[5]Sculpin were also found to be the largest fish consumed by the seals. Bearded seals are capable of preying on pelagic anddemersal fish in addition to their benthic prey.[16]
Bearded seals give birth in the spring. In theCanadian Arctic, seal pupping occurs in May.[9] In Svalbard, bearded seals reachsexual maturity at 5 or 6 years of age.[17] Further south, inAlaska, most pups are born in late April.[clarification needed] Pups are born on small drifting ice floes in shallow waters, usually weighing around 30–40 kg (66–88 lb). They enter the water only hours after they are born, and quickly become proficient divers. Mothers care for the pups for 18–24 days, during which time the pups grow at an average rate of 3.3 kg (7.3 lb) per day. During this time, pups consume an average of 8 L (1.8 imp gal; 2.1 US gal) of milk a day. By the time they are weaned, the pups have grown to about 100 kg (220 lb).
Just before the pups are weaned, a new mating cycle takes place. Females ovulate at the end of their lactation period, but remain close to their pups, ready to defend them if necessary. During the mating season, male seals will "sing", emitting a long-drawn-out warbling note that ends in a sort of moan or sigh. This sound may attract females, or may be used by the males to proclaim their territory or their readiness for breeding. Males occupy the same areas from one year to the next.[18]
Like many Arctic mammals, bearded seals employ a reproductive strategy known asdelayed implantation. This means that theblastocyst is not implanted for two months after fertilization, most often becoming implanted in July. Thus, the seal's totalgestation period is around eleven months, though its active gestation period is nine months.[19]
Natural predators of the bearded seal include polar bears, who rely on these seals as a major food source.[5]Killer whales also prey on these seals, sometimes overturning ice floes to reach them.Walruses also eat these seals, mainly pups, but such predation is rare.[20]
Bearded seals are believed to live up to 31 years.[21]
The vocalizations produced by the bearded seal are unique, possibly because theirtrachea is different from that of other Northern Pacificphocids. A majority of the rings in the trachea are incomplete with only a membrane attaching the two ends.[22]
Sample of underwater bearded seal vocalizations taken using a hydrophone
The sounds of the bearded seal usually consist of a longoscillating trill lasting for a minute or more followed by a short, deep moan. This "song" is often repeated frequently.[22] The number of call types within a population can vary geographically, with four types found in Svalbard and eleven in the Western Canadian Arctic. The most frequent sounds are trills, moans, and sweeps. A sweep can be compared to a short trill.[23]
Bearded seals produce distinct trills from late March to late June, with a decline inrhythmicity in late May and June. This timeline coincides with their breeding and pupping season, which is from April to May. The repetitive and transmittable nature of bearded seal trills leads researchers to believe that they are utilized for communication, likely duringcourtship and breeding.[24] Males use these sounds to establish mating territories and communicate their fitness,[23] but it is likely that females produce these sounds as well.[24]
Underwater, bearded seal trills can be heard from a distance of over 30 km (19 mi), with some types of sounds traveling farther than others. This makes it possible for one animal to communicate with another animal that is far away, although acoustic degradation does occur as the sound passes through the environment. A seal must produce a trill with asound-pressure of at least 100 dB at 1 m in order for the sound to propagate 30 km, meaning that bearded seals can likely produce sounds at this level.[24]
On March 28, 2008, the U.S.National Marine Fisheries Service initiated a status review[25] under theEndangered Species Act (ESA) to determine if listing this species under the ESA is warranted. All bearded seals are protected under theMarine Mammal Protection Act, and determined by theIUCN to be classified as a "least concern" for extinction.[2] This classification was determined due to various factors including, widespread distribution, stable population size, as well as alternating prey resources.NOAA determined that the factors influencing any change in conservancy status of the bearded seal may include: loss of sea ice by climate change,bycatch from commercial fishing gear, and hunting.[26] Their main predators includepolar bears; however, typically pups around age 2 are attacked within birthing lairs, leaving older juveniles and adults commonly unharmed.[27] Due to climate change, factors such as loss of sea ice, as well as decrease in prey population may create negative results on the bearded seal population in the future. Therefore, monitoring of the species as well as influences of human activity, will be vital to ensure species stability.
There are two recognized subspecies of this seal:[1]
Image
Subspecies
Distribution
Erignathus barbatus barbatus(Erxleben 1777) – Eastern bearded seal
Erignathus barbatus nauticus(Pallas 1811) – Western bearded seal
While the validity of these subspecies has been questioned, and is not yet supported by any molecular data,[4] analysis of the animals' calls does indicate a differentiation between different populations.[23]
Bearded seal fossils have been found to be as old as the early to midPleistocene. These early fossils were found in northern regions like England, Alaska, and Sweden, as well as theNorth Sea and theChamplain Sea.[28]
Bearded seals, like all true seals, belong to the family Phocidae which is one of the three families in the clade Pinnipedia, along withOtariidae andOdobenidae. Pinnipeds are thought to have originated 27 to 25 million years ago during the lateOligocene period. One hypothesis for the evolution of pinnipeds is that pinnipeds are a diphyletic group and otariids and odobenids are more closely related to bears, and phocids are more closely related to mustelids like weasels. Another hypothesis suggests that pinnipeds are a monophyletic group that descended from a single ancestor. This has been more supported by phylogenetic analysis than the diphylectic hypothesis. One such study suggests that phocids aresister taxa to the common ancestor to both otariids and odobenids.[28]
Bearded seals belong to the subfamilyPhocinae (Northern Hemisphere seals). Phocinae can be further divided into three clades: Erignathini (bearded seals), Cystophorini (hooded seals), and Phocini (all remaining genera). Bearded seals are the sister taxa to the common ancestor of Cystophorini and Phocini.[29]
^abBerta, A. & Churchill, M. (2012). "Pinniped Taxonomy: evidence for species and subspecies".Mammal Review.42 (3):207–234.doi:10.1111/j.1365-2907.2011.00193.x.
^Ryg, Morten; Lydersen, Christian; Markussen, Nina H.; Smith, Thomas G.; Øritsland, Nils Are (18 January 1990). "Estimating the Blubber Content of Phocid Seals".Canadian Journal of Fisheries and Aquatic Sciences.47 (6):1223–1227.Bibcode:1990CJFAS..47.1223R.doi:10.1139/f90-142.ISSN0706-652X.
^Lowry, Lloyd F.; Frost, Kathryn J.; Burns, John J. (1980). "Variability in the Diet of Ringed Seals, Phoca hispida, in Alaska".Canadian Journal of Fisheries and Aquatic Sciences.37 (12):2254–2261.Bibcode:1980CJFAS..37.2254L.doi:10.1139/f80-270.ISSN0706-652X.
^Saundry, Peter. 2010.Bearded sealArchived July 4, 2010, at theWayback Machine. Encyclopedia of Earth. Topic editor C. Michael Hogan, Ed.in Chief: Cutler Cleveland, NCSE, Washington DC
^Nuttal; et al. (2005).Encyclopedia of the Arctic. New York, NY: Routlelege.
^Perry, Judith E. (1983).Seals of the World. Ithaca, NY: Comstock Publishing Associates. p. 103.
^Folkens, Peter (2002).National Audubon Society Guide to Marine Mammals of the World. New York. p. 117.{{cite book}}: CS1 maint: location missing publisher (link)
^"Bearded Seals".National Marine Mammal Laboratory. Retrieved1 May 2016.
^abcRisch, Denise; Clark, Christopher W.; Corkeron, Peter J.; Elepfandt, Andreas; Kovacs, Kit M.; Lydersen, Christian; Stirling, Ian; Van Parijs, Sofie M. (May 2007). "Vocalizations of male bearded seals, Erignathus barbatus: classification and geographical variation".Animal Behaviour.73 (5):747–762.doi:10.1016/j.anbehav.2006.06.012.ISSN0003-3472.S2CID53187110.
^abcCleator, Holly J.; Stirling, Ian; Smith, T. G. (5 July 1989). "Underwater vocalizations of the bearded seal (Erignathus barbatus)".Canadian Journal of Zoology.67 (8):1900–1910.Bibcode:1989CaJZ...67.1900C.doi:10.1139/z89-272.ISSN0008-4301.
Heptner, V. G.; Nasimovich, A. A; Bannikov, Andrei Grigorevich; Hoffmann, Robert S,Mammals of the Soviet Union, Volume II, part 3 (1996). Washington, D.C. : Smithsonian Institution Libraries and National Science Foundation
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