Ross seal (Ommatophoca rossii)

Description

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Ross seal fact file

• Description
• Biology
• Range
• Habitat
• Status
• Threats
• Conservation
• Find out more
• Glossary
• References
• Print factsheet

Ross seal description

Occupying remote, inaccessible ice packs surrounding the Antarctic, the Ross seal is perhaps the most enigmatic phocid (earless seals) ^{(1) (3)}. This seal displays a number of characteristics that distinguish it from similar species, including proportionately large eye sockets, although the eyes are actually of average size, very short fur, and long fore- and hind-flippers ^{(2) (3)}. It also has a relatively small head with a short, wide, blunt-ended snout and small, touch-sensitive whiskers on each lip ^{(3) (4)}. The mouth is relatively small and armed with short, backward curving teeth, used to hold onto its slippery squid prey ⁽³⁾. After its annual moult, the fur coat of the Ross seal is dark greyish to black on the back, and silver on the belly, with attractive brown to reddish streaks stretching from the lower jaw to the chest ^{(3) (4)}. Throughout the year this coat may fade to a tan or brownish colour ⁽²⁾. The young pups, however, are born with a downy coat of long, thick and soft fur that fades to yellow on the belly ⁽³⁾. 

On land the Ross seal is slow and sluggish, and crawls on its belly by grasping onto the ice with short, black claws. Not capable of an upright stance, it often assumes a posture with the head raised, and the mouth open and pointing upwards, and it is due to this behaviour that this seal has often been referred to as the ‘singing seal’ ⁽³⁾.  

Also known as

big-eyed seal, singing seal.

Size

Male length: 1.68 – 2.08 m ⁽²⁾

Female length: 1.90 – 2.50 m ⁽²⁾

Male weight: 129 – 216 kg ⁽²⁾

Female weight: 159 – 204 kg ⁽²⁾

Ross seal biology

Unlike many other Antarctic seal species, the Ross seal is largely solitary and does not congregate in large colonies to breed. Instead, single females haul out onto the ice between November and December to give birth to the single pup that was conceived the previous season, with pupping peaking between 3^rdand 18^th December. The pup is nursed on the mother’s energy-rich milk and is capable of swimming very soon after birth ⁽³⁾. The females mate again in late December, probably in the water, but implantation of the fertilised egg is delayed for two to three months, allowing the female to moult, feed and gain valuable weight before the foetus develops ^{(2) (3)}. The young pup weans after around a month, and most females will mate at three years of age, while males mature at two to three years. The Ross seal has a life expectancy of up to 21 years ⁽²⁾. 

On land this seal has no predators, but in the water it may fall prey to orcas (Orcinus orca) or leopard seals (Hydrunga leptonyx). The Ross seal itself preys largely on cephalopods, although it may also sometimes feed upon fish and krill, and this specialised diet allows this seal to avoid competition with other marine mammals. Its prey is captured at depths of between 100 and 200 metres after a prolonged dive, which lasts for around six minutes ⁽³⁾. 

This seal displays a variety of vocalisations which may be used for communication between seals or to warn off predators. When approached by people on land, it may open its mouth widely and emit a series of trills and thumping noises. This warning call is often accompanied by an aggressive posture, with the teeth displayed and the chest thrusted outwards, making the seal appear larger in size. In the water this seal makes a variety of chirps, and it had been suggested that these may be used to defend territories from other Ross seals, although the solitary nature of this species suggests that this is unlikely ⁽²⁾. Explosive noises, pulsed chugs and siren calls are also used by the Ross seal, some of which are used during mating and in communication between the mother and pup ⁽³⁾.

Ross seal range

The Ross seal has a circumpolar distribution surrounding the Antarctic in the Southern Ocean ⁽¹⁾. From late summer, some individuals may migrate northwards towards open ocean, and some vagrants have been sighted as far north as South Georgia, the Falkland Island and the South Sandwich Islands ^{(1) (5)}.

Ross seal habitat

For much of the year the Ross seal is found on remote, inaccessible packs of dense ice, upon which it hauls out to moult and breed. From late summer through to mid-spring this seal spends more time in open ocean, sometimes travelling as far as 2,000 kilometres away from the ice to feed ^{(1) (5) (6)}. 

Ross seal status

Classified as Least Concern (LC) on the IUCN Red List ⁽¹⁾.

Ross seal threats

The remoteness of the Ross seal’s habitat has meant that this species has been largely sheltered from most of the detrimental activities commonly associated with human contact. Indeed, there has been no known commercial exploitation of this seal, and it has only been subject to scientific collection on a handful of occasions, with the harvesting of 20 to 30 individuals between 1986 to 1987 one notable event ^{(1) (3) (7)}. However, one consequence of the species’ remoteness is that there is very little known of its status, although it is thought to be the least abundant of all Antarctic seals ^{(1) (3)}. One of the more recent surveys estimated a global population of around 130,000, but other studies have provided hugely variable data, with population estimates ranging from 20,000 to almost 230,000 ^{(1) (8)}. 

The main threat to this Antarctic seal is likely to be global climate change ^{(1) (9)}. With a future increase in sea surface temperature likely, it could be expected that the prevalence of pack ice will decline. This will impact upon the Ross seal through the loss of ice packs upon which it gives birth and avoids predators. It is also possible that climate change may cause a change in the distribution and abundance of its prey species, but at this moment in time, the exact way in which climate change will impact the Ross seal and other Antarctic marine mammals is very unclear ⁽⁹⁾.

Ross seal conservation

Due to this species’ non-threatened status, it is not currently the target of any specific conservation measures. However, the Ross seal is protected by the Convention for the Conservation of Antarctic Seals, which protects against over-harvesting from commercial exploitation if it were to begin, and the Environmental Protection Protocol of the Antarctic Treaty, which prohibits mining and oil drilling activity in the region for at least 50 years, as well as the dumping of refuse ^{(1) (7) (10)}.

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

Find out more

To find out more about the Ross seal, see:

• The Seal Conservation Soceity: 
  http://www.pinnipeds.org/species/ross.htm
• Marine Mammals of the World:
  http://nlbif.eti.uva.nl/bis/marine_mammals.php?menuentry=soorten&id=60

For more information on the conservation of the Falklands Islands and South Georgia, see:

• FalklandsConservation:
  http://www.falklandsconservation.com/
• The South Georgia Heritage Trust:
  http://www.sght.org/

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Glossary

Cephalopod

From the Greek for ‘head-foot’, a class of molluscs that occur only in marine habitats. All species have grasping tentacles, and either an internal or external shell. Includes nautiloids, cuttlefish, squids, octopuses, and extinct ammonites and belemnites.

Fertilisation

The fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.

Vagrant

Found occasionally outside normal range.

References

1. IUCN Red List (June, 2010)
   http://www.iucnredlist.org/
2. Nowak, R.M. (1999) Walker’s Mammals of the World. The Johns Hopkins University Press, Baltimore.
3. Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (1999) Encyclopedia of Marine Mammals. Academic Press, London.
4. Marine Mammals of the World (June, 2010)
   http://nlbif.eti.uva.nl/bis/marine_mammals.php?menuentry=soorten&id=60
5. Stewart, B.S. (2007) A Summary of Status of Knowledge of the Biology, Distribution and Abundance of the Ross Seal, Ommatophoca rossii. SCAR Expert Group on Seals, Norway.
6. Blix, A.S. and Nordoy, E.S. (2007) Ross Seal (Ommatophoca rossii) annual distribution, diving behaviour, breeding and moulting, off Queen Maud Land, Antarctica. Polar Biology, 30: 1449-1458.
7. The Seal Conservation Society (June, 2010)
   http://www.pinnipeds.org/species/ross.htm
8. 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, IUCN, Gland, Switzerland and Cambridge, UK.
9. 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.
10. British Antarctic Survey (June, 2010)
    http://www.antarctica.ac.uk/about_antarctica/geopolitical/treaty/update_1972.php