|Scientific Name:||Lobodon carcinophaga (Hombron & Jacquinot, 1842)|
Lobodon carcinophagus (Hombron & Jacquinot, 1842) [orth. error]
|Taxonomic Notes:||Rice (1998) states that the correct spelling of the specific name is carcinophaga, not the previously more widely used carcinophagus.|
|Red List Category & Criteria:||Least Concern ver 3.1|
|Facilitator/Compiler(s):||Lowry, L., Ahonen, H., Pollock, C.M., Chiozza, F. & Battistoni, A.|
Due to its widespread occurrence and very large population size, the Crabeater Seal should remain classified by IUCN as Least Concern.
|Previously published Red List assessments:|
|Range Description:||The distribution of Crabeater Seals is tied to seasonal fluctuations of the pack ice. They can be found right up to the coast and ice shelves of Antarctica, as far south as the Bay of Whales (Lindsey 1938), during late summer ice break-up. They occur in greatest numbers in the seasonally shifting pack ice surrounding the Antarctic continent. As vagrants they travel as far north as New Zealand and the southern coasts of Africa, Australia and South America. Crabeater Seals have been known to occasionally wander far inland and die in the dry valleys adjacent to McMurdo Sound. A live animal was found 113 km from open water at an elevation of 920 m asl, and carcasses have been found as high as 1,100 m asl (Kooyman 1981, Rice 1998).|
Vagrant:Argentina; Australia; Bouvet Island; Brazil; Chile; Falkland Islands (Malvinas); Heard Island and McDonald Islands; New Zealand; South Africa; South Georgia and the South Sandwich Islands; Uruguay
|FAO Marine Fishing Areas:|
Atlantic – Antarctic; Atlantic – southeast; Atlantic – southwest; Indian Ocean – eastern; Indian Ocean – western; Indian Ocean – Antarctic; Pacific – southeast; Pacific – southwest; Pacific – Antarctic
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||The Crabeater Seal is a widespread species, and, as is the case for other Seals inhabiting the Antarctic pack ice, population assessments are very difficult and expensive to conduct and therefore infrequently undertaken. Published global population estimates range from two million (Scheffer 1958) up to 50-75 million animals (Erickson et al. 1971). However, early estimates were based on very limited sampling and were highly speculative. The most recent available data, obtained during the multi-national effort conducted under the umbrella of the Antarctic Pack Ice Seal program in the late 1990s, provided a population size estimate of approximately 8,000,000 animals for the area surveyed (Southwell et al. 2012). Considering that major areas of the pack ice around the continent were not surveyed, there is a large uncertainty regarding the actual population size of the species. Yet, Crabeater Seals are considered to be one of the most abundant seal species (if not the most abundant) and one of the most numerous large mammals on Earth.|
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Adult Crabeater Seals reach 2.6 m in length and weigh an estimated 200-300 kg. Neonates are thought to be at least 1.1 m and 20-40 kg. The mean age of sexual maturity in females varies from 2.5 to 4.2 years and these variations may be related to changes in food abundance (Bengtson and Laws 1985, Hårding and Härkönen 1995). Annual adult mortality is about 3-10% (Boveng 1993). Crabeater Seal births occur mainly during the second half of October. They do not use specific rookeries. Instead, adult females haul out singly on an ice floe where they give birth, and they are joined by a male shortly after (Siniff et al. 1979, Adam 2005). Adult males attend female-pup pairs and stay with the female until her oestrous begins one to two weeks after the pup is weaned. Mating has not been witnessed and presumably occurs in the water.|
Pups are born from September to December (Southwell et al. 2003) in a soft woolly coat that is greyish-brown in colour and has been described as light, milk coffee brown, with darker colouring on the flippers. Adult females fast during lactation, and wean their pups after an average of three weeks (Southwell 2004, Adam 2005) at which time pups are moulting from the lanugo coat into a sub-adult pelage similar to that of the adult. Adults and subadults moult in January and February, and a large proportion of the animals in an area are thought to be hauled out during the annual moult.
Mortality is high in the first year, possibly reaching 80%. Much of this mortality is attributed to Leopard Seal predation, and up to 78% of Crabeaters that survive through their first year have injuries and scars from Leopard Seal attacks (Siniff and Bengtson 1997). The presence of long scars and sets of parallel scars that are readily visible on the pale, relatively unmarked pelage of Crabeaters, are testimony to the frequency of these attacks on young of this species. Leopard Seal attacks appear to fall off dramatically after Crabeaters reach one year of age (Siniff and Stone 1985).
Recent research has revealed that Crabeater Seals can dive up to 600 m and stay submerged for 24 minutes, although most feeding dives occur within the top 50 m, and are shorter in duration (Burns et al. 2004, 2008). Foraging occurs primarily at night (Bengtson and Stewart 1992), and instrumented seals have been recorded to dive continuously for periods up to 16 hours. Dives at dawn and dusk are deeper than at night, and indicate that Crabeater feeding activity is also tied to the daily vertical migrations of Krill. They have a general pattern of feeding from dusk until dawn, and hauling-out in the middle of the day.
Crabeater Seals feed primarily on Antarctic Krill, Euphausia superba, which accounts for over 90% of their diet, with the remainder made up of fish and squid. New information indicates that the diet composition of the Crabeater Seal can display some plasticity, and they can compensate when Krill availability decreases by incorporating more fish (>25% of their diet; Hückstädt et al. 2012). All of the post-canine teeth are ornate, with multiple accessory cusps that interlock to form a network for straining Krill from the seawater. A ridge of bone on each mandible fills the gap in the mouth behind the last upper post-canine teeth and the back of the jaw, which helps prevent the loss of Krill from the mouth when feeding.
Crabeater Seals are frequently encountered alone or in small groups of up to three on the ice or in the water. Much larger groups of up to 1,000 hauled-out together have been observed. They can be seen swimming together in herds estimated to be up to 500 animals, breathing and diving almost synchronously.
|Continuing decline in area, extent and/or quality of habitat:||No|
|Generation Length (years):||14.9|
|Movement patterns:||Not a Migrant|
|Use and Trade:||Several brief episodes of commercial harvesting of Crabeaters ended when they were determined to be economically unsuccessful.|
There are currently no direct threats from human activity throughout most of the species’ normal range.
A mass die-off of Crabeater Seals was reported from an area near a research base on the Antarctic Peninsula in 1955 (Laws and Taylor 1957). About 3,000 animals were trapped in areas five to 25 km from open water and most died over a two to three month period. None of the animals examined appeared to be starving, and numerous abortions of foetuses were noted. A disease outbreak was suspected, but never identified. Antibodies to canine distemper virus were found in Crabeater Seals from this area in 1989 (Bengtson et al. 1991).
The effects of global climate change on Antarctic seals are unknown. Learmonth et al. (2006) suggest that Crabeater Seal numbers may decline with increasing temperatures if Antarctic sea ice is significantly reduced. Loss of sufficient areas of pack ice habitat used for pupping, resting, avoidance of predators, and access to preferred foraging areas because of changes from warming could lead to population declines. The loss of sea ice has the potential to negatively impact Crabeater Seals given their high level of specialization on Antarctic Krill. Sea ice coverage is of particular importance for the survival of juvenile stages of Krill, and ultimately determines the biomass of adult Krill that is available for higher trophic level predators. It is unclear whether Crabeater Seals might be able to switch from their highly specialized, Krill-based diet, to a more generalist strategy with rapid loss of sea ice. The effects of loss of large amounts of ice on the Antarctic continent, general climate warming, or sea level rise, on Antarctic Ocean circulation and productivity and on Antarctic marine resources such as seals are unknown.
Seasonal tourism in the Antarctic and Sub-Antarctic has increased steadily in the last 30 plus years, and is currently at all-time high levels. The effects of increased vessel noise, disturbance from vessel passage, and close approach by people in small boats and on land on Crabeater Seal behaviour, distribution and foraging are unknown. There is a small risk of injury to animals from collision with boats or crushing from large vessel passage through ice fields.
There are no reports of significant interactions between Crabeater Seals and fisheries. Commercial harvest of Krill may pose a threat to Crabeater Seals, if it ever becomes established at a large scale.
|Conservation Actions:||The Crabeater Seal is not listed as endangered or threatened on any National Red List. Crabeater Seals are protected by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals and any future commercial harvest would have to be regulated through these international agreements (Reijnders et al. 1993).|
Adam, P. 2005. Lobodon carcinophaga. Mammalian Species 772: 1-14.
Bengtson, J.L. and Laws, R.M. 1985. Trends in crabeater seal age at maturity: an insight into Antarctic marine interactions. In: W.R. Siegfried, P.R. Condy and R.M. Laws (eds), Antarctic nutrient cycles and food webs, pp. 669-674. Springer-Verlag, Berlin.
Bengtson, J.L., and Stewart, B.S. 1992. Diving and haulout behavior of crabeater seals in the Weddell Sea, Antarctica during March 1986. Polar Biology 12: 635-644.
Bengtson, J.L.,, Boveng, P., Franzen, U., Have, P., Heide-Jørgensen, M.P. and Härkönen, T.J. 1991. Antibodies to canine distemper virus in Antarctic seals. Marine Mammal Science 7: 85-87.
Burns, J.M., Costa, D.P., Fedak, M.A., Hindell, M.A., Bradshaw, C.J., Gales, N.J. and Crocker, D.E. 2004. Winter habitat use and foraging behavior of crabeater seals along the Western Antarctic Peninsula. Deep Sea Research Part II: Topical Studies in Oceanography 51(17): 2279-2303.
Burns, J.M., Hindell, M.A., Bradshaw, C.J.A. and Costa, D.P. 2008. Fine-scale habitat selection of crabeater seals as determined by diving behavior. Deep Sea Research Part II: Topical Studies in Oceanography 55(3): 500-514.
Erickson, A. W., Siniff, D. B., Cline, D. R. and Hofman, R. J. 1971. Distributional ecology of Antarctic seals. In: G. Deacon (ed.), Symposium on Antarctic Ice and Water Masses, pp. 55-76. Sci. Comm. Antarct Res., Cambridge, UK.
Hårding, K. C. and Härkönen, T. 1995. Estimating mean age at sexual maturity in the crabeater seal (Lobodon carcinophagus). Canadian Journal of Fisheries and Aquatic Sciences 52: 2347-2352.
Hückstädt, L.A., Burns, J.M., Koch, P.L., McDonald, B.I., Crocker, D.E. and Costa, D.P. 2012. Diet of a specialist in a changing environment: the crabeater seal along the western Antarctic Peninsula. Marine Ecology Progress Series 455: 287-301.
IUCN. 2015. The IUCN Red List of Threatened Species. Version 2015-4. Available at: www.iucnredlist.org. (Accessed: 19 November 2015).
Kooyman, G. L. 1981. Crabeater seal Lobodon carcinophagus (Hombron and Jacquinot, 1842). In: S. H. Ridgway and R. Harrison (eds), Handbook of marine mammals, pp. 221-235. Academic Press, London, UK.
Laws, R. M. 1977. The significance of vertebrates in the Antarctic marine ecosystem. In: G. A. Llano (ed.), Adaptations within Antarctic ecosystems, Gulf Publishing Co. for the Smithsonian Inst., Washington, DC., Washington, DC., USA.
Laws, R.M. and Taylor, R.J.F. 1957. A mass dying of crabeater seals, Lobodon carcinophagus (Gray). Proceedings of the Zoological Society of London 129: 315-324.
Learmonth, J.A., Macleod, C.D., Santos, M.B., Pierce, G.J., Crick, H.Q.P. and Robinson, R.A. 2006. Potential effects of climate change on marine mammals. Oceanography and Marine Biology: An Annual Review 44: 431-464.
Pacifici, M., Santini, L., Di Marco, M., Baisero, D., Francucci, L., Grottolo Marasini, G., Visconti, P. and Rondinini, C. 2013. Generation length for mammals. Nature Conservation 5: 87–94.
Reijnders, P., Brasseur, S., van der Toorn, J., van der Wolf, P., Boyd, I., Harwood, J., Lavigne, D. and Lowry, L. 1993. Seals, fur seals, sea lions, and walrus. Status survey and conservation action plan. IUCN Seal Specialist Group.
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Siniff, D.B. and Bengtson, J.L. 1977. Observations and hypotheses concerning the interactions among crabeater seals, leopard seals and killer whales. Journal of Mammalogy 58: 414-416.
Siniff, D.B., Stirling, I., Bengtson, J.L. and Reichle, R.A. 1979. Social and reproductive behavior of crabeater seals (Lobodon carcinophagus) during the austral spring. Canadian Journal of Zoology 57: 2243-2255.
Southwell, C., Bengtson, J. Bester, M., Blix, A.S., Bornemann, H., Boveng, P., Cameron, M., Forcada, J., Laake, J., Nordøy, E., Plötz, J., Rogers, T., Southwell, D., Steinhage, D., Stewart, B.S. and Trathan, P. 2012. A review of data on abundance, trends in abundance, habitat use and diet of ice-breeding seals in the Southern Ocean. CCAMLR Science 19: 49-74.
Southwell, C. J. 2004. Satellite dive recorders provide insights into the reproductive strategies of crabeater seals (Lobodon carcinophagus). Journal of Zoology (London) 264: 399-402.
Southwell, C., Kerry, K., Ensor, P., Woehler, E.J. and Rogers, T. 2003. The timing of pupping by pack-ice seals in East Antarctica. Polar Biology 26: 648-652.
Southwell, C., Paxton C. G. M., Borchers, D., Boveng, P. and de la Mare, W. 2008. Taking account of dependent species in management of the Southern Ocean krill fishery: estimating crabeater seal abundance off east Antarctica. Journal of Applied Ecology 45: doi:10.1111/j.1365-2664.2007.01399.x.
|Citation:||Hückstädt, L. 2015. Lobodon carcinophaga. The IUCN Red List of Threatened Species 2015: e.T12246A45226918.Downloaded on 23 October 2017.|
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