Ommatophoca rossii 

Scope: Global
Language: English

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Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Chordata Mammalia Carnivora Phocidae

Scientific Name: Ommatophoca rossii (Gray, 1844)
Common Name(s):
English Ross Seal

Assessment Information [top]

Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2015
Date Assessed: 2014-09-30
Assessor(s): Hückstädt, L.
Reviewer(s): Kovacs, K.M.
Facilitator/Compiler(s): Lowry, L., Ahonen, H., Pollock, C.M., Chiozza, F. & Battistoni, A.
The most recent circumpolar estimate of Ross Seal abundance indicates a total population of over 78,000 individuals. There is no indication of a declining trend in the population. However, abundance estimates are somewhat dated and have considerable uncertainty around them and therefore, the population trend is unknown. Ross Seals depend on sea ice for reproduction and at some time in the future they could be adversely affected by a reduction in sea ice due to continued climate warming. The Ross Seal is a widespread and abundant species that does not qualify for any of the IUCN threatened categories, thus they should be listed as Least Concern.
Previously published Red List assessments:

Geographic Range [top]

Range Description:Ross Seals have a circumpolar distribution in Southern Ocean waters surrounding Antarctica. In the summer, they are usually seen in dense consolidated pack ice where they haul out to breed, moult and rest. Satellite tracking suggests that Ross Seals spend several months each year foraging in the open ocean in association with the Antarctic Polar Front (Blix and Nordøy 2007). Vagrants have been reported from many sub-Antarctic islands including the South Sandwich Islands, the South Orknies, and Falkland, Scott, Kerguelen and Heard Islands, as well as from southern Australia (Rice 1998, Thomas 2002).
Countries occurrence:
Australia; Falkland Islands (Malvinas); French Southern Territories (Kerguelen); Heard Island and McDonald Islands; South Georgia and the South Sandwich Islands (South Sandwich Is.)
FAO Marine Fishing Areas:
Atlantic – southwest; Atlantic – Antarctic; Indian Ocean – Antarctic; Pacific – Antarctic
Additional data:
Estimated area of occupancy (AOO) - km2:20665464Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:33459698
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:No
Upper elevation limit (metres):3Lower depth limit (metres):792
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Ross Seals typically haul out in dense consolidated pack ice and are spread over large geographic areas. As these areas can usually only be reached by ice-breaking ships or long-range aircraft, it is difficult to estimate population size and trend with high certainty. Published global population estimates range from 20,000-50,000 (Scheffer 1958) up to 220,000 animals (Gilbert and Erickson 1977). However, early estimates were based on very limited sampling and were highly speculative. Analysis of ship and aerial sighting surveys carried out around the Antarctic Continent between 1968 and 1983 provided an estimate for the global population of Ross Seals in the pelagic pack ice of the Southern Ocean in the order of 130,000 animals (Erickson and Hanson 1990). No indication of the uncertainty around that estimate was given. The most ambitious and coordinated effort to determine abundance of this species to date was the Antarctic Pack-Ice Seal (APIS) project which conducted aerial and shipboard surveys around the continent during 1996-2001. This international programme also included deployment of satellite-linked dive recorders to investigate haulout behaviour. APIS surveys resulted in an estimate of 78,500 (95% CL 39,400-231,200) Ross Seals in the surveyed areas (Southwell et al. 2012). Given the uncertainty in the estimates, only gross changes in Ross Seal population size could be confidently detected from repeated surveys (Southwell et al. 2008). New data from genetic studies estimating the effective population size of the species indicate a larger population size for the Ross Seal than that estimated using traditional population size surveys (Curtis et al. 2011), but those methods have not been rigorously tested.
Current Population Trend:Unknown
Additional data:
Number of mature individuals:40000Continuing decline of mature individuals:No
Extreme fluctuations:NoPopulation severely fragmented:No

Habitat and Ecology [top]

Habitat and Ecology:At maturity, Ross Seals are the smallest of the four Antarctic phocids. Based on a small sample of measured animals, Ross Seal males reach 1.68-2.09 m in length and 129-216 kg and females are slightly larger at 1.96-2.5 m in length and 159-204 kg. It is estimated that pups are about one metre and 16 kg at birth; eight suckling pups examined in November were 109-138 cm in length and 40-75 kg. Age at sexual maturity is thought to be three to four years for females and two to seven years for males (Ray 1981). Adults reach final body size at approximately nine years of age and can live to at least 20 years (Skinner and Klages 1994).

Most pups are born in November, with a peak from early to mid-November (Southwell et al. 2003). Weaning takes place at about one month of age, although little is known of the relationship between mother and pup. Nursing pups have been seen swimming between ice floes so they appear to be aquatic to some degree. Mating is thought to occur in the water, but has not been observed. Although this species has been presumed to be polygynous, genetic studies do not support this hypothesis and indicate a monogamous mating system (Curtis et al. 2011). Moulting is believed to occur in January, at which time many Ross Seals appear to fast (Skinner and Klages 1994), and moulting seals can form large aggregations on ice floes. During summer Ross Seals exhibit a diel haulout pattern with most seals hauled out on the ice at midday (Ray 1981, Bengtson and Stewart 1997, Southwell 2003). Satellite tracking suggests that Ross Seals are pelagic foragers, spending months in the open ocean foraging in association with the Antarctic Polar Front  and returning to the pack-ice to breed in October-November (Blix and Nordøy 2007).

Recent work using electronic devices to monitor at-sea behaviour of Ross Seals has revealed that the species dives continuously throughout the day (average of 108 dives per day), frequently reaching depths of 100–300 m, and displays a clear diel pattern in their diving depth. The deepest dive recorded for the species was 792 m, while the longest dives were over 30 minutes in duration (Blix and Nordøy 2007). The diet of Ross Seals is largely unknown, but the limited available data indicate that they eat mostly squid, with lesser amounts of fish and some invertebrates including krill (Ray 1981, Southwell et al. 2012). Skinner and Klages (1994) identified only Antarctic Silverfish (Pleurogramma antarcticum) in 20 animals examined; no other fish were present. Several species of squid were also recorded in this latter study, but many stomachs were empty when the animals were collected in January, suggesting that this species eats little or fasts entirely during the post-breeding moult period.

Killer Whales and Leopard Seals are presumed to be predators of the Ross Seal.
Systems:Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat:No
Generation Length (years):8.6
Movement patterns:Not a Migrant

Use and Trade [top]

Use and Trade: This species is not used at present.

Threats [top]

Major Threat(s): Ross Seals are typically found hauled out in dense consolidated pack ice and can usually only be reached by icebreakers. Small numbers of animals have been collected for commercial purposes, scientific studies and museums, but otherwise interactions with humans have been few. When wandering outside the pack ice zone, Ross Seals could come in contact with commercial fishing operations, but there are no reports of interactions to date.

Ross Seals have antibodies to phocine herpesvirus confirming some exposure, but in the only available study they did not have antibodies to Trichinella, Toxoplasma, or phocine distemper virus (Tryland et al. 2012).

Our very limited knowledge about the species makes it difficult to make any projections about how global climate change might affect the Ross Seal. However, Learmonth et al. (2006) suggest that Ross Seal numbers may decline with increasing temperatures if Antarctic sea ice is significantly reduced. Siniff et al. (2008) suggest that they will be among the least impacted of the Antarctic seals because they do not feed in sea-ice covered areas. Climate change will affect them when loss of sufficient areas of consolidated ice habitat used for pupping, resting, and avoidance of predators comes to a critical level. Further, due to their pelagic nature, reductions of sea ice would imply longer travel distances to reach their preferred foraging areas. The effects of loss of large amounts of ice on the Antarctic continent, general climate warming, or sea level rises on Antarctic Ocean circulation and productivity and on Antarctic marine resources such as seals are largely unknown.

Conservation Actions [top]

Conservation Actions: Ross seals are protected by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals, and are not listed as threatened or endangered on any national Red List.

Citation: Hückstädt, L. 2015. Ommatophoca rossii. The IUCN Red List of Threatened Species 2015: e.T15269A45228952. . Downloaded on 21 September 2018.
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