Hauling-out

Last updated August 24, 2023

Hauling-out is a behaviour associated with pinnipeds (true seals, sea lions, fur seals and walruses) temporarily leaving the water.^[1]^[2] Hauling-out typically occurs between periods of foraging activity.^[1]^[3]^[4] Rather than remain in the water, pinnipeds haul-out onto land or sea-ice for reasons such as reproduction and rest.^[4]^[2] Hauling-out is necessary in seals for mating (with the exception of the Baikal seal ^[1]) and giving birth (although a distinction is generally made between reproductive aggregations, termed "rookeries", and non-reproductive aggregations, termed "haul-outs").^[4]^[5] Other benefits of hauling-out may include predator avoidance, thermoregulation, social activity, parasite reduction and rest.^[4]^[2]^[5]^[6]

There is much variation in haul-out patterns among different seal species.^[1] Haul-out sites may be segregated by age and sex within the same species.^[3] Many species of pinniped have only a few localized rookeries where they breed, but periodically occupy hundreds of haul-out sites throughout the range.^[5] For example, the Australian fur seals breed on only nine islands in Bass Strait but also occupy up to 50 haul-out sites in south-east Australian waters,^[4] and Steller sea lions have around 50 rookeries throughout their range, but several hundred haul-out sites.^[5] Hauling-out behaviour provides numerous benefits to pinnipeds besides reproduction. This behaviour has been shown to be used for activities such as thermoregulation, predator avoidance, moulting, nursing, and resting.^[2] Haul-out frequency, duration, and site location (i.e. sea-ice, floating-ice, and terrestrial) are all influenced by physical constraints (i.e. air temperature, wind speed, and time of day) and biological constraints (i.e. moulting, age, and sex).^[2]^[7]^[6]^[8]^[9] Variations in hauling-out behaviour exist among pinnipeds for reasons such as geographical location.^[7]

Examples

Weddell seals

Haul-out sites of Weddell seals are not necessarily geographically distinct from one another and vary due to physical factors (i.e. food availability) and biological factors (i.e. age).^[7] Weddell seals are high latitude Antarctic inhabitants, allowing them to haul-out onto ice as adults year round for foraging.^[7] Similar to other pinnipeds, Weddell seals haul-out for reasons such as feeding, rest, avoidance of predators, and thermoregulation.^[7]^[10] Seasonal variation has been indicated to influence the haul-out patterns of this species, environmental factors such as air temperature and wind speed trigger a shift from long-duration diurnal haul-outs to short-duration nocturnal patterns.^[7] Following moulting season the number of haul-outs performed increases allowing the seals to benefit from the increased air temperature and thus decreasing the energetic cost of growing new hair.^[7]^[10] The haul-out patterns of female Weddell seal are heavily influenced by the age of their pups.^[10]^[6] In the first week post parturition, haul-out frequency is high and females remain hauled-out for longer periods prior to the pups starting to swim. Haul-out frequency decreases as the pups are weaned and mating begins.^[7]^[10]^[6]

Walruses

Walruses tend to occupy both terrestrial and sea ice haul-out sites, alternating between the two depending on resource availability.^[8] Walruses haul-out onto land primarily for birthing, moulting, nursing, and resting, meanwhile using sea-ice haul-out sites for foraging and predator avoidance.^[8]^[11] These physiological factors are correlated with both the duration and frequency of haul-outs among walruses.^[8] Sea ice sites are more commonly used for shorter and more frequent haul-outs compared to terrestrial sites, which are commonly used to fulfill more time-consuming requirements (i.e. breeding and birthing).^[8]^[11] Hauling-out is also used as a method of thermoregulation, therefore it is influenced by various environmental factors such as wind speed, temperature, and even time of day.^[8] Accounting for these environmental factors, walruses more frequently haul-out from late morning to early evening and avoid hauling-out during weather periods of intense cold or high winds.^[8]^[11] Haul-out frequency is at a maximum for walruses during the summer using terrestrial haul-out sites as sea ice sites are then further from foraging grounds.^[8]^[11] As female walruses haul-out for parturition, the males are territorial of the haul-out site surrounding the female herd.^[11] In these instances, hauling-out provides an opportunity for more aggressive and territorial males to mate.^[12]

Ringed seal

Ringed seal hauling-out occurs throughout any point in the year, however it reaches a maximum during the spring.^[9] In comparison to other pinniped species, ringed seals haul-out with a shorter duration year round.^[9] Ringed seals have a diel haul-out pattern in which they spend more time hauled-out during the night, an uncommon feature among pinnipeds.^[9]^[13] Hauling-out spikes an increase in the herding behaviour of ringed seals, particularly in the Ladoga subspecies.^[14] Subspecies of the ringed seal prefer different haul-out sites depending on their geographical location and environmental constraints.^[15] For example, 5 subspecies of ringed seals prefer hauling-out onto land-fast ice, however Phoca hispida ochotensis prefers drifting pack ice, meanwhile Phoca hispida hispida occupies both land-fast ice and far offshore areas of relatively stable ice.^[15] The majority of ringed seals however use terrestrial haul-out sites to create birth layers in the snow for newborn seal pups.^[15]

Harbour seal

Harbour seals are the most abundant pinniped in the eastern North Pacific Ocean.^[2] Much like other pinnipeds, harbour seals haul-out for reasons such as thermoregulation, breeding, mating, moulting, resting, and foraging.^[16]^[2] They commonly haul-out onto intertidal ledges, mudflats, beaches, and ice floes year round.^[16] Haul-out sites are often revisited on a regular basis by the same herd^[2] and are heavily affected by tide height.^[2]^[16] Harbour seals are likely to move haul-out sites in response to inclement weather conditions (i.e. wind chill and wave size) to more favourable sites in rocky reefs, mudflats, and beaches that are exposed during lower tides.^[2]^[16] Frequency and duration of the behaviour is at a maxima during early afternoon when lower tides and higher air temperatures are prevalent.^[2]^[16] During parturition and weaning, females spend more time hauled-out ashore until their pups begin to swim, meanwhile males spend less time hauled-out and maintain aquatic territories instead.^[2] Moulting and predation risk also increase the time spent hauled-out.^[2] Despite the increased time ashore for females and decreased time ashore or males during birthing and weaning, biological constraints such as age and sex have not been shown to effect harbour seal haul-outs.^[2] Both male and female harbour seals of all ages are consistent with time spent hauled-out.^[2]^[16] Harbour seals commonly inhabit regions susceptible to human disturbances (i.e. industries such as the fishery), a factor that has been studied and shown to alter haul-out patterns.^[17] Human disturbances negatively influence the duration and frequency of harbour seal haul-outs, decreasing the occurrence of this behaviour as human interference increases.^[17]

Related Research Articles

<span class="mw-page-title-main">Earless seal</span> Family of mammals

The earless seals, phocids, or true seals are one of the three main groups of mammals within the seal lineage, Pinnipedia. All true seals are members of the family Phocidae. They are sometimes called crawling seals to distinguish them from the fur seals and sea lions of the family Otariidae. Seals live in the oceans of both hemispheres and, with the exception of the more tropical monk seals, are mostly confined to polar, subpolar, and temperate climates. The Baikal seal is the only species of exclusively freshwater seal.

An eared seal, otariid, or otary is any member of the marine mammal family Otariidae, one of three groupings of pinnipeds. They comprise 15 extant species in seven genera and are commonly known either as sea lions or fur seals, distinct from true seals (phocids) and the walrus (odobenids). Otariids are adapted to a semiaquatic lifestyle, feeding and migrating in the water, but breeding and resting on land or ice. They reside in subpolar, temperate, and equatorial waters throughout the Pacific and Southern Oceans, the southern Indian, and Atlantic Oceans. They are conspicuously absent in the north Atlantic.

Sea lions are pinnipeds characterized by external ear flaps, long foreflippers, the ability to walk on all fours, short and thick hair, and a big chest and belly. Together with the fur seals, they make up the family Otariidae, eared seals. The sea lions have six extant and one extinct species in five genera. Their range extends from the subarctic to tropical waters of the global ocean in both the Northern and Southern Hemispheres, with the notable exception of the northern Atlantic Ocean. They have an average lifespan of 20–30 years. A male California sea lion weighs on average about 300 kg (660 lb) and is about 2.4 m (8 ft) long, while the female sea lion weighs 100 kg (220 lb) and is 1.8 m (6 ft) long. The largest sea lions are Steller's sea lions, which can weigh 1,000 kg (2,200 lb) and grow to a length of 3.0 m (10 ft). Sea lions consume large quantities of food at a time and are known to eat about 5–8% of their body weight at a single feeding. Sea lions can move around 16 knots in water and at their fastest they can reach a speed of about 30 knots. Three species, the Australian sea lion, the Galápagos sea lion and the New Zealand sea lion, are listed as endangered.

Pinnipeds, commonly known as seals, are a widely distributed and diverse clade of carnivorous, fin-footed, semi-aquatic, and mostly marine mammals. They comprise the extant families Odobenidae, Otariidae, and Phocidae, with 34 extant species and more than 50 extinct species described from fossils. While seals were historically thought to have descended from two ancestral lines, molecular evidence supports them as a monophyletic lineage. Pinnipeds belong to the clade Caniformia of the order Carnivora; their closest living relatives are musteloids, having diverged about 50 million years ago.

<span class="mw-page-title-main">Steller sea lion</span> Species of carnivore

The Steller sea lion is a large, near-threatened species of sea lion, predominantly found in the coastal marine habitats of the northeast Pacific Ocean and the Pacific Northwest regions of North America, from north-central California to Oregon, Washington and British Columbia to Alaska. Their range continues across the Northern Pacific and the Aleutian Islands, all the way to Kamchatka, Magadan Oblast, and the Sea of Okhotsk, south to Honshu’s northern coastline. It is the sole member of the genus Eumetopias, and the largest of the so-called eared seals (Otariidae). Among pinnipeds, only the walrus and the two species of elephant seal are bigger. The species is named for the naturalist and explorer Georg Wilhelm Steller, who first described them in 1741. Steller’s sea lions have attracted considerable attention in recent decades, both from scientists and the general public, due to significant declines in their numbers over an extensive portion of their northern range—notably in Alaska.

The Baikal seal, Lake Baikal seal or nerpa, is a species of earless seal endemic to Lake Baikal in Siberia, Russia. Like the Caspian seal, it is related to the Arctic ringed seal. The Baikal seal is one of the smallest true seals and the only exclusively freshwater pinniped species. A subpopulation of inland harbour seals living in the Hudson Bay region of Quebec, Canada, as well as the Saimaa ringed seal and the Ladoga seal, are also found in fresh water, but these seals are part of species that also have marine populations.

The ringed seal is an earless seal inhabiting the Arctic and sub-Arctic regions. The ringed seal is a relatively small seal, rarely greater than 1.5 m in length, with a distinctive patterning of dark spots surrounded by light gray rings, hence its common name. It is the most abundant and wide-ranging ice seal in the Northern Hemisphere, ranging throughout the Arctic Ocean, into the Bering Sea and Okhotsk Sea as far south as the northern coast of Japan in the Pacific and throughout the North Atlantic coasts of Greenland and Scandinavia as far south as Newfoundland, and including two freshwater subspecies in northern Europe. Ringed seals are one of the primary prey of polar bears and killer whales, and have long been a component of the diet of indigenous people of the Arctic.

The bearded seal, also called the square flipper seal, is a medium-sized pinniped that is found in and near to the Arctic Ocean. It gets its generic name from two Greek words that refer to its heavy jaw. The other part of its Linnaean name means bearded and refers to its most characteristic feature, the conspicuous and very abundant whiskers. When dry, these whiskers curl very elegantly, giving the bearded seal a "raffish" look.

The harp seal, also known as Saddleback Seal or Greenland Seal, is a species of earless seal, or true seal, native to the northernmost Atlantic Ocean and Arctic Ocean. Originally in the genus Phoca with a number of other species, it was reclassified into the monotypic genus Pagophilus in 1844. In Greek, its scientific name translates to "ice-lover from Greenland," and its taxonomic synonym, Phoca groenlandica translates to "Greenlandic seal." This is the only species in the genus Pagophilus.

The Australian sea lion, also known as the Australian sea-lion or Australian sealion, is a species of sea lion that is the only endemic pinniped in Australia. It is currently monotypic in the genus Neophoca, with the extinct Pleistocene New Zealand sea lion Neophoca palatina the only known congener. With a population estimated at around 14,730 animals, the Wildlife Conservation Act of Western Australia (1950) has listed them as “in need of special protection”. Their Conservation status is listed as endangered. These pinnipeds are specifically known for their abnormal breeding cycles, which are varied between a 5-month breeding cycle and a 17-18 month aseasonal breeding cycle, compared to other pinnipeds which fit into a 12-month reproductive cycle. Females are either silver or fawn with a cream underbelly and males are dark brown with a yellow mane and are bigger than the females.

Phoca is a genus of the earless seals, within the family Phocidae, source of the French name for seal, 'phoque'. It now contains just two species, the common seal and the spotted seal. Several species formerly listed under this genus have been split into the genera Pusa, Pagophilus, and Histriophoca. Until recently, Phoca largha has been considered a subspecies of Phoca vitulina but now is considered its own species. For this reason, the fossil history of the genus is unclear, and it has formerly been used as wastebasket taxon for a number of fossils of uncertain affinity.

The Weddell seal is a relatively large and abundant true seal with a circumpolar distribution surrounding Antarctica. The Weddell seal was discovered and named in the 1820s during expeditions led by British sealing captain James Weddell to the area of the Southern Ocean now known as the Weddell Sea. The life history of this species is well documented since it occupies fast ice environments close to the Antarctic continent and often adjacent to Antarctic bases. It is the only species in the genus Leptonychotes.

The Caspian seal is one of the smallest members of the earless seal family and unique in that it is found exclusively in the brackish Caspian Sea. It lives along the shorelines, but also on the many rocky islands and floating blocks of ice that dot the Caspian Sea. In winter and cooler parts of the spring and autumn season, it populates the northern Caspian coastline. As the ice melts in the summer and warmer parts of the spring and autumn season, it also occurs in the deltas of the Volga and Ural Rivers, as well as the southern latitudes of the Caspian where the water is cooler due to greater depth.

The ribbon seal is a medium-sized pinniped from the true seal family (Phocidae). A seasonally ice-bound species, it is found in the Arctic and Subarctic regions of the North Pacific Ocean, notably in the Bering Sea and Sea of Okhotsk. It is distinguished by its striking coloration, with two wide white strips and two white circles against dark brown or black fur.

The Saimaa ringed seal is a subspecies and glacial relict of ringed seal. They are among the most endangered seals in the world, having a total population of only about 400 individuals. The only existing population of these seals is found in Lake Saimaa, Finland. They have lived in complete isolation from other ringed seal species for around 9,500 years and have diverged into a morphologically and ecologically different subspecies of ringed seal. The population is descended from ringed seals that were separated from the rest when the land rose after the last ice age. This seal, along with the Ladoga seal and the Baikal seal, is one of the few living freshwater seals.

The Ladoga ringed seal is a freshwater subspecies of the ringed seal found entirely in Lake Ladoga in northwestern Russia. The Ladoga ringed seal was isolated in freshwater lakes and separated from the Arctic ringed seal as a result of the isostatic rebound of the region following the end of the Weichselian Glaciation.

Pagophily or pagophilia is the preference or dependence on water ice for some or all activities and functions. The term Pagophila is derived from the Ancient Greek pagos meaning "sea-ice", and philos meaning "-loving".

Freshwater seals are pinnipeds which live in freshwater bodies. The group is paraphyletic in nature, the uniting factor being the environment in which these pinnipeds live. The vast majority of all modern seals live solely in saltwater habitats though this is likely due to the rarity of sufficiently large freshwater bodies rather than the limitation of seal biology.

The harborseal, also known as the common seal, is a true seal found along temperate and Arctic marine coastlines of the Northern Hemisphere. The most widely distributed species of pinniped, they are found in coastal waters of the northern Atlantic and Pacific oceans, Baltic and North seas.

The Arctic ringed seal is a subspecies of ringed seals. Arctic ringed seals inhabit the Arctic Ocean, and are the most abundant and wide-ranging seal in the Northern Hemisphere. The ringed seal species is the smallest true seal, and gets its name from a distinctive patterning of light spots on dark grey colored fur. The ringed seal is commonly preyed upon by Polar bears, Arctic foxes, and Killer whales. Population estimates and survival rates are unknown, but average life expectancy is 15-28 years. Ringed seals have long been a component of the diet of indigenous people of the Arctic. Arctic ringed seals have been listed as threatened on the Endangered Species Act since 2012, and increasingly face loss of their habitat due to shrinking ice and snow cover.

References

1 2 3 4 Hoelzel, A. Rus. (2002). Marine Mammal Biology: An Evolutionary Approach. Blackwell Publishing. ISBN 978-0-632-05232-5. p. 197.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 London, Josh M.; Ver Hoef, Jay M.; Jefferies, Steven J.; Lance, Monique M.; Boveng, Peter L. (June 18, 2012). "Haul-Out Behavior of Harbor Seals (Phoca vitulina) in Hood Canal, Washington". PLOS ONE. 7 (6): e38180. Bibcode:2012PLoSO...738180L. doi: 10.1371/journal.pone.0038180 . PMC 3377645 . PMID 22723851.
1 2 Kovacs, Kit M.; Jonas, Krista M.; Welke, Sylvia E. (1990). "Sex and age segregation by Phoca vitulina concolor at haul-out sites during the breeding season in the Passamaquoddy Bay region, New Brunswick". Marine Mammal Science. 6 (3): 204–214. doi:10.1111/j.1748-7692.1990.tb00244.x.
1 2 3 4 5 Gales, Nick; Gales, Nicholas; Hindell, Mark; & Kirkwood, Roger. (2003). Marine Mammals: Fisheries, Tourism and Management Issues. CSIRO Publishing. ISBN 978-0-643-06953-4. p. 259.
1 2 3 4 Loughlin, Thomas R.; Rugh, David J.; Fiscus, Clifford H. (1984). "Northern Sea Lion Distribution and Abundance: 1956-80". The Journal of Wildlife Management. 48 (3): 729–740. doi:10.2307/3801420. JSTOR 3801420.
1 2 3 4 Thomas, Jeanette; DeMaster, Douglas (1983). "Diel haul-out patterns of Weddell seal (Leptonychotes weddelli) females and their pups". Canadian Journal of Zoology. 61 (9): 2084–2086. doi:10.1139/z83-273.
1 2 3 4 5 6 7 8 Boeheme, Lars; Baker, Amy; Fedak, Mike; Ârthun, Marius; Nicholls, Keith; Robinson, Patrick; Costa, Dan; Biuw, Martin; Photopoulou, Theoni (2016). "Bimodal Winter Haul-Out Patterns of Adult Weddell Seals (Leptonychotes weddellii) in the Southern Weddell Sea". PLOS ONE. 11 (5): e0155817. Bibcode:2016PLoSO..1155817B. doi: 10.1371/journal.pone.0155817 . PMC 4873014 . PMID 27196097.
1 2 3 4 5 6 7 8 Udevitz, Mark; Chadwick, Jay; Fischbach, Anthony; Garlich-Miller, Joel (2009). "Modeling haul-out behavior of walruses in Bering Sea ice". Canadian Journal of Zoology. 87 (12): 1111–1128. doi:10.1139/Z09-098.
1 2 3 4 Born, E. W.; Teilmann, J.; Riget, F. (2002). "Haul-out activity of Ringed seals (Phoca hispida) determined form satellite telemetry". Marine Mammal Science. 18 (1): 167–181. doi:10.1111/j.1748-7692.2002.tb01026.x.
1 2 3 4 Lake, S.E.; Burton, H.R.; Hindell, M.A. (1997). "Influence of time of day and month on Weddell seal haul-out patterns at the Vestfold Hills, Antarctica". Polar Biology. 18 (5): 319–324. doi:10.1007/s003000050194. S2CID 20280920.
1 2 3 4 5 Hamilton, Charmain; Kovacs, Kit; Lydersen, Christian (2015). "Year-round haul-out behaviour of male walruses Odobenus rosmarus in the Northern Barents Sea". Marine Ecology Progress Series. 519: 251–263. Bibcode:2015MEPS..519..251H. doi: 10.3354/meps11089 .
↑ Charrier, Isabelle; Burlet, Armandine; Aubin, Thierry (2011). "Social vocal communication in captive Pacific walruses Odobenus rosmarus divergens". Mammalian Biology. 76 (5): 622–627. doi:10.1016/j.mambio.2010.10.006.
↑ Smith, T. G. "Population dynamics of the ringed seal in the Canadian eastern Arctic". Fisheries Research Board of Canada Bulletin. 181: 55.
↑ Sipilä, Tero; Medvedev, Nikolai; Hyvärinen, Heikki (1996). "The Ladoga seal (Phoca hispida ladogensis Nordq.)". Hydrobiologia. 322 (1–3): 193–198. doi:10.1007/bf00031827. S2CID 26024676.
1 2 3 Smith, Thomas; Stirling, Ian (1975). "The breeding habitat of the ringed seal (Phoca hispida). The birth lair and associated structures". Canadian Journal of Zoology. 53 (9): 1297–1305. doi:10.1139/z75-155.
1 2 3 4 5 6 Terhune, John (1987). "Meteorological influences on harbour seal haul-out". Aquatic Mammals. 13 (3): 114–118.
1 2 Härkönen, T. J. (1987). "Influence of feeding on haul-out patterns and sizes of sub-populations in harbour seals". Netherlands Journal of Sea Research. 21 (4): 331–339. Bibcode:1987NJSR...21..331H. doi:10.1016/0077-7579(87)90007-x.

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[:Hoelzel-1] 1 2 3 4 Hoelzel, A. Rus. (2002). Marine Mammal Biology: An Evolutionary Approach. Blackwell Publishing. ISBN 978-0-632-05232-5. p. 197.

[:A-2] 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 London, Josh M.; Ver Hoef, Jay M.; Jefferies, Steven J.; Lance, Monique M.; Boveng, Peter L. (June 18, 2012). "Haul-Out Behavior of Harbor Seals (Phoca vitulina) in Hood Canal, Washington". PLOS ONE. 7 (6): e38180. Bibcode:2012PLoSO...738180L. doi: 10.1371/journal.pone.0038180 . PMC 3377645 . PMID 22723851.

[:Kovacs-3] 1 2 Kovacs, Kit M.; Jonas, Krista M.; Welke, Sylvia E. (1990). "Sex and age segregation by Phoca vitulina concolor at haul-out sites during the breeding season in the Passamaquoddy Bay region, New Brunswick". Marine Mammal Science. 6 (3): 204–214. doi:10.1111/j.1748-7692.1990.tb00244.x.

[:Gales-4] 1 2 3 4 5 Gales, Nick; Gales, Nicholas; Hindell, Mark; & Kirkwood, Roger. (2003). Marine Mammals: Fisheries, Tourism and Management Issues. CSIRO Publishing. ISBN 978-0-643-06953-4. p. 259.

[:Loughlin-5] 1 2 3 4 Loughlin, Thomas R.; Rugh, David J.; Fiscus, Clifford H. (1984). "Northern Sea Lion Distribution and Abundance: 1956-80". The Journal of Wildlife Management. 48 (3): 729–740. doi:10.2307/3801420. JSTOR 3801420.

[:3-6] 1 2 3 4 Thomas, Jeanette; DeMaster, Douglas (1983). "Diel haul-out patterns of Weddell seal (Leptonychotes weddelli) females and their pups". Canadian Journal of Zoology. 61 (9): 2084–2086. doi:10.1139/z83-273.

[:1-7] 1 2 3 4 5 6 7 8 Boeheme, Lars; Baker, Amy; Fedak, Mike; Ârthun, Marius; Nicholls, Keith; Robinson, Patrick; Costa, Dan; Biuw, Martin; Photopoulou, Theoni (2016). "Bimodal Winter Haul-Out Patterns of Adult Weddell Seals (Leptonychotes weddellii) in the Southern Weddell Sea". PLOS ONE. 11 (5): e0155817. Bibcode:2016PLoSO..1155817B. doi: 10.1371/journal.pone.0155817 . PMC 4873014 . PMID 27196097.

[:4-8] 1 2 3 4 5 6 7 8 Udevitz, Mark; Chadwick, Jay; Fischbach, Anthony; Garlich-Miller, Joel (2009). "Modeling haul-out behavior of walruses in Bering Sea ice". Canadian Journal of Zoology. 87 (12): 1111–1128. doi:10.1139/Z09-098.

[:7-9] 1 2 3 4 Born, E. W.; Teilmann, J.; Riget, F. (2002). "Haul-out activity of Ringed seals (Phoca hispida) determined form satellite telemetry". Marine Mammal Science. 18 (1): 167–181. doi:10.1111/j.1748-7692.2002.tb01026.x.

[:2-10] 1 2 3 4 Lake, S.E.; Burton, H.R.; Hindell, M.A. (1997). "Influence of time of day and month on Weddell seal haul-out patterns at the Vestfold Hills, Antarctica". Polar Biology. 18 (5): 319–324. doi:10.1007/s003000050194. S2CID 20280920.

[:5-11] 1 2 3 4 5 Hamilton, Charmain; Kovacs, Kit; Lydersen, Christian (2015). "Year-round haul-out behaviour of male walruses Odobenus rosmarus in the Northern Barents Sea". Marine Ecology Progress Series. 519: 251–263. Bibcode:2015MEPS..519..251H. doi: 10.3354/meps11089 .

[:6-12] Charrier, Isabelle; Burlet, Armandine; Aubin, Thierry (2011). "Social vocal communication in captive Pacific walruses Odobenus rosmarus divergens". Mammalian Biology. 76 (5): 622–627. doi:10.1016/j.mambio.2010.10.006.

[:10-13] Smith, T. G. "Population dynamics of the ringed seal in the Canadian eastern Arctic". Fisheries Research Board of Canada Bulletin. 181: 55.

[:8-14] Sipilä, Tero; Medvedev, Nikolai; Hyvärinen, Heikki (1996). "The Ladoga seal (Phoca hispida ladogensis Nordq.)". Hydrobiologia. 322 (1–3): 193–198. doi:10.1007/bf00031827. S2CID 26024676.

[:9-15] 1 2 3 Smith, Thomas; Stirling, Ian (1975). "The breeding habitat of the ringed seal (Phoca hispida). The birth lair and associated structures". Canadian Journal of Zoology. 53 (9): 1297–1305. doi:10.1139/z75-155.

[:11-16] 1 2 3 4 5 6 Terhune, John (1987). "Meteorological influences on harbour seal haul-out". Aquatic Mammals. 13 (3): 114–118.

[:12-17] 1 2 Härkönen, T. J. (1987). "Influence of feeding on haul-out patterns and sizes of sub-populations in harbour seals". Netherlands Journal of Sea Research. 21 (4): 331–339. Bibcode:1987NJSR...21..331H. doi:10.1016/0077-7579(87)90007-x.

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