| Ross seal | |
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| Ross seal off Wilkes Land, Antarctica | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Clade: | Pinnipedia |
| Family: | Phocidae |
| Genus: | Ommatophoca Gray, 1844 |
| Species: | O. rossii |
| Binomial name | |
| Ommatophoca rossii (Gray, 1844) | |
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| Ross seal range | |
TheRoss seal (Ommatophoca rossii) is atrue seal (family Phocidae) with a range confined entirely to thepack ice ofAntarctica. It is theonly species of the genusOmmatophoca. First described during theRoss expedition in 1841, it is the smallest, least abundant and least well known of the Antarctic pinnipeds. Its distinctive features include disproportionately large eyes, whence its scientific name (Ommato- meaning "eye", andphoca meaning "seal"), and complex, trilling and siren-like vocalizations. Ross seals arebrachycephalic as they have a short broad muzzle, and also have shorter fur than any other seal.
The Ross seal shares a recent common ancestor with three other extant Antarctic seals, which are together known as thelobodontine seals. The other species are thecrabeater seal (Lobodon carcinophaga),leopard seal (Hydrurga leptonyx) andWeddell seal (Leptonychotes weddelli).[2] These species, collectively belonging to the sealtribe Lobodontini, share teeth adaptations, including lobes and cusps useful for straining smaller prey items out of the water column. The ancestral Lobodontini likely diverged from its sisterclade,Mirounga (elephant seals) in the lateMiocene to earlyPliocene, when they migrated southward and diversified rapidly in relative isolation around Antarctica.[2] However, the only fossils of Ross seals so far known date from much later, during the earlyPleistocene of New Zealand.[3]
Ross seals reach a length of about 1.68–2.09 m (5.5–6.9 ft) and weight of 129–216 kg (284–476 lb); females are slightly larger at 1.96–2.5 m (6.4–8.2 ft).[1] A molecular genetic based technique has been established to confirm the sex of individuals in the laboratory.[4] Pups are about 1 m and 16 kg at birth. The coat is colored dark-brown in the dorsal area and silvery-white beneath. At the onset of the Antarctic winter, the coat fades gradually to become light brown. At close range, the Ross seal can be easily identified by its large eyes, which are up to 7 cm in diameter. They also have shorter muzzles.
The Ross seal is able to produce a variety of complex twittering and siren-like sounds that are performed on ice and underwater, where they carry for long distances.[5] The underwater siren sound can be composed of two harmonically unrelated superimposed tones that are pulsed with the same rhythm. Uniquely, the vocalizations, whether on ice or in water, are made with a closed mouth - emitting no air. The purpose of these sounds is unknown, though their distinctive nature and long range are likely to facilitate either encounters or avoidance of individuals.[5]
Although its close relativesWeddell seals,crabeater seals andleopard seals are ubiquitous in Antarctic waters, the Ross seal is an uncommon and relatively unknown animal, considered to be the least commonpack ice seal. It almost never leaves theAntarctic Ocean, with the very rare exception of stray animals found aroundsubantarctic islands, and uniquely, off the south coast ofAustralia. Nonetheless, its distribution is circumpolar, with individuals found in low densities - usually singly - in very thick pack ice in all regions of the continent.
The total Ross seal population is estimated at around 130,000 individuals, but there is great uncertainty in this estimate (reported 95%confidence intervals range from 20,000 to 227,000).[6] Thus, very little is known about trends in the population. A genetic survey did not detect evidence of a recent, sustained genetic bottleneck in this species,[7] which suggests that populations do not appear to have suffered a detectable and sustained decline in the recent past.
Interactions with humans have been limited. They have been collected historically by Antarctic expeditions and for scientific collections. Their range does not generally overlap with commercial fishing.
Ross seal feeds primarily onsquid andfish, primarilyAntarctic silverfish, in thepelagic zone.[8] Ross seals are presumed to be preyed upon bykiller whales (Orcinus orca) and leopard seals, large predators that share their Antarctic habitat, though there are no documented observations of predation. Haul-out behavior among Ross seals varies seasonally, with a preference for midday haul-outs observed in certain months (September, October, February, and December). Additionally, during the breeding season, female seals entering the pack ice engage in continuous haul-outs lasting 5 to 7 days. These periods are occasionally interrupted by brief water entries lasting 1 to 3 hours, indicating a potential alternation between capital and facultative income breeding strategies.[9]
Females give birth to their young on the ice in November. Pups are nursed for only four weeks beforeweaning. Mating is thought to occur underwater shortly after the pup is weaned, but has never been observed. Ross seals mature sexually at approximately three years of age, and are thought to live around 20 years in the wild.[8]
Authority control databases: National |
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