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Lobodon carcinophaga

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Taxonomy [top]

Kingdom Phylum Class Order Family
ANIMALIA CHORDATA MAMMALIA CARNIVORA PHOCIDAE

Scientific Name: Lobodon carcinophaga
Species Authority: (Hombron & Jacquinot, 1842)
Common Name(s):
English Crabeater Seal
Synonym(s):
Lobodon carcinophagus (Hombron & Jacquinot, 1842) [orth. error]
Taxonomic Notes: Rice (1998) states that the correct spelling of the specific name is carcinophaga, not the recently more widely used carcinophagus. He provides a review of the history of this issue.

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2008
Date Assessed: 2008-06-30
Assessor(s): Southwell, C. (IUCN SSC Pinniped Specialist Group)
Reviewer(s): Kovacs, K. & Lowry, L. (Pinniped Red List Authority)
Justification:
Due to its widespread occurrence and very large population size, the Crabeater Seal should remain classified as Least Concern.

IUCN Evaluation of the Crabeater Seal, Lobodon carcinophaga
Prepared by the Pinniped Specialist Group



A. Population reduction Declines measured over the longer of 10 years or 3 generations
A1 CR > 90%; EN > 70%; VU > 50%
Al. Population reduction observed, estimated, inferred, or suspected in the past where the causes of the reduction are clearly reversible AND understood AND have ceased, based on and specifying any of the following:
(a) direct observation
(b) an index of abundance appropriate to the taxon
(c) a decline in area of occupancy (AOO), extent of occurrence (EOO) and/or habitat quality
(d) actual or potential levels of exploitation
(e) effects of introduced taxa, hybridization, pathogens, pollutants, competitors or parasites.

Age-structure data for crabeater seals are limited, so the generation time cannot be calculated precisely. Sexual maturity is thought to be attained at 2.5-4 years of age and a maximum longevity possibly up to 25-30 years, the average age of reproducing individuals should be at least 10 years. A population reduction of crabeater seals has not been observed, estimated, inferred, or suspected in the past 30 years. However, population abundance is not precisely known and has not been closely monitored.

A2, A3 & A4 CR > 80%; EN > 50%; VU > 30%
A2. Population reduction observed, estimated, inferred, or suspected in the past where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.

A population reduction of crabeater seals has not been observed, estimated, inferred, or suspected in the past 30 years.

A3. Population reduction projected or suspected to be met in the future (up to a maximum of 100 years) based on (b) to (e) under A1.

A population reduction of crabeater seals could occur some time in the future if sea ice habitats decline due to continued climate warming. However, while sea ice extent presently appears to be declining in western Antarctica, it may be increasing in eastern Antarctica, and overall there appears to be no change yet in the extent of Southern Ocean sea ice.

A4. An observed, estimated, inferred, projected or suspected population reduction (up to a maximum of 100 years) where the time period must include both the past and the future, and where the causes of reduction may not have ceased OR may not be understood OR may not be reversible, based on (a) to (e) under A1.

A population reduction of Crabeater Seals has not been observed, estimated, inferred, or suspected in the past 30 years.

B. Geographic range in the form of either B1 (extent of occurrence) AND/OR B2 (area of occupancy)
B1. Extent of occurrence (EOO): CR < 100 km²; EN < 5,000 km²; VU < 20,000 km²

The EOO of Crabeater Seals is > 20,000 km².

B2. Area of occupancy (AOO): CR < 10 km²; EN < 500 km²; VU < 2,000 km²

The AOO of Crabeater Seals is > 2,000 km².

AND at least 2 of the following:
(a) Severely fragmented, OR number of locations: CR = 1; EN < 5; VU < 10
(b) Continuing decline in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) area, extent and/or quality of habitat; (iv) number of locations or subpopulations; (v) number of mature individuals.
(c) Extreme fluctuations in any of: (i) extent of occurrence; (ii) area of occupancy; (iii) number of locations or subpopulations; (iv) number of mature individuals.

C. Small population size and decline
Number of mature individuals: CR < 250; EN < 2,500; VU < 10,000

The current abundance of Crabeater Seals is certainly > 10,000.

AND either C1 or C2:
C1. An estimated continuing decline of at least: CR = 25% in 3 years or 1 generation; EN = 20% in 5 years or 2 generations; VU = 10% in 10 years or 3 generations (up to a max. of 100 years in future)
C2. A continuing decline AND (a) and/or (b):
(a i) Number of mature individuals in each subpopulation: CR < 50; EN < 250; VU < 1,000
or
(a ii) % individuals in one subpopulation: CR = 90–100%; EN = 95–100%; VU = 100%
(b) Extreme fluctuations in the number of mature individuals.

D. Very small or restricted population
Number of mature individuals: CR < 50; EN < 250; VU < 1,000 AND/OR restricted area of occupancy typically: AOO < 20 km² or number of locations < 5

The current abundance of Crabeater Seals is certainly > 1,000. AOO is > 20 km² and the number of locations is > 5.

E. Quantitative analysis
Indicating the probability of extinction in the wild to be: Indicating the probability of extinction in the wild to be: CR > 50% in 10 years or 3 generations (100 years max.); EN > 20% in 20 years or 5 generations (100 years max.); VU > 10% in 100 years

There has been no quantitative analysis of the probability of extinction for Crabeater Seals.

Listing recommendationPast and recent estimates of Crabeater Seal abundance indicate a total population size of several million within their circumpolar distribution. There is no indication of a declining trend in the population, although broad-scale estimates have considerable uncertainty around them, and consequently trend estimates are also uncertain. Crabeater Seals depend on sea ice for reproduction and could be adversely affected by a reduction in sea ice due to continued climate warming at some time in the future. However, presently there appears to be no consistent circumpolar trend in Southern Ocean sea ice habitat. The Crabeater Seal is a widespread and abundant species that does not qualify for any of the threatened categories in the near future, Crabeater Seals should be listed as Least Concern.
History:
1996 Lower Risk/least concern (Baillie and Groombridge 1996)

Geographic Range [top]

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 of Antarctica, as far south as McMurdo Sound, 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. Crabeaters 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 above sea level, and carcasses have been found as high as 1,100 m above sea level (Kooyman 1981, Rice 1998, Bengtson 2002).
Countries:
Native:
Antarctica
Vagrant:
Argentina; Australia; Bouvet Island; Brazil; Falkland Islands (Malvinas); Heard Island and McDonald Islands; New Zealand; South Africa; South Georgia and the South Sandwich Islands; Uruguay
FAO Marine Fishing Areas:
Native:
Atlantic – Antarctic; Atlantic – southwest; Indian Ocean – Antarctic; Pacific – Antarctic
Range Map: Click here to open the map viewer and explore range.

Population [top]

Population: The crabeater seal is a widespread species and, and as is the case for other Antarctic seals inhabiting the pack ice, population assessments are very difficult and expensive to conduct and therefore infrequently undertaken. Published global population estimates range from 2 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 global estimate, from analysis of ship and aerial sighting surveys carried out around the continent between 1968 and 1983, provided a point estimate for global crabeater seal population size in the pelagic pack ice of the Southern Ocean of 7,000,000 animals (Erickson and Hanson 1990). But, the authors acknowledged this estimate was negatively biased due to inadequate correction for haulout and suggested a more reasonable estimate was likely to be in the order of 11-12 million. This estimate is likely to have considerable uncertainty associated with it. A recent regional survey in East Antarctica between 64-150°E indicated a 95% confidence interval of 700,000-1,400,000 around a point estimate of 950,000 animals (Southwell et al. in press). Given this uncertainty, only large changes in crabeater seal population size could be confidently detected from repeated surveys.
Population Trend: Unknown

Habitat and Ecology [top]

Habitat and Ecology: Adults 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). Births occur mainly during the second half of October. Annual mortality is about 14.5% (Laws 1977b).

There are no specific rookeries and females haul-out singly on ice to give birth. Adult males attend female-pup pairs and stay with the female until her estrous one to two weeks after the pup is weaned. Mating has not been witnessed and presumably occurs in the water. Females are reported to bite males around the mouth and flippers and this may account for the abundant small scars on the faces of older males.

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. They are weaned in approximately three weeks (Southwell 2004) at which time they are moulting or just beginning their moult from the lanugo coat. The pup sheds into a sub-adult pelage similar to that of the adult.

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. The presence of long scars and sets of parallel scars which 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.

Recent research has revealed that crabeater seals can dive to 430 m and stay submerged for 11 minutes, although most feeding dives were to 20-30 m, and shorter in duration. Foraging occurs primarily at night, and instrumented seals have been recorded to regularly 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 and 95% of their diet is made up of this species. Small amounts of fish and squid are also part of the diet. 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 faeces are routinely a pinkish red, from their krill diet and reddish stains are frequently seen on the ice near where they are hauled-out.

Crabeaters are frequently encountered alone or in small groups of up to three on the ice or in the water. However, 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. They are the only Antarctic phocid species that is highly gregarious. The moult is in January and February. A large proportion of the animals in an area are thought to be hauled-out during the annual moult.
Systems: Terrestrial; Marine

Threats [top]

Major Threat(s): Crabeater seals are considered to be the most abundant seal species and one of the most numerous large mammals on earth.

A mass die-off was reported from an area near a base on the Antarctic Peninsula in 1955. About 3,000 animals were trapped in areas 5-25 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. In the 1980s a study revealed antibodies to canine distemper virus (CDV) in crabeater seals from this area. Leopard seals have also tested positive for antibodies to CDV. Weddell seals have been tested, but thus far there has not been a positive result. Ross seals have not been tested. Outbreaks of a similar distemper virus in the North Atlantic led to mass die-offs of harbour seals in the 1980s (Bengtson and Boveng 1991).

Several brief episodes of commercial harvesting of crabeaters ended when they were determined to be economically unsuccessful. Commercial harvest of krill may pose a threat to crabeater seals, if it ever becomes established at a large scale. There are currently no direct threats from human activity throughout most of the species’ normal range (Bengtson 2002).

The effects of global climate change on Antarctic seals are unknown. However, 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 (possible) and access to preferred foraging areas because of changes from warming could lead to population declines of crabeater seals. 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 vessels 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 on significant fisheries interactions.

Conservation Actions [top]

Conservation Actions: The crabeater seal is not listed as endangered or threatened. 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).

Citation: Southwell, C. (IUCN SSC Pinniped Specialist Group) 2008. Lobodon carcinophaga. The IUCN Red List of Threatened Species. Version 2014.3. <www.iucnredlist.org>. Downloaded on 24 November 2014.
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