TRUE SEALS

Ross Seal (Ommatophoca rossii)

The Ross Seal (Ommatophoca rossii) is an Antarctic species with a range encircling the Antarctic continent, typically seen hauling out on pack ice. The name Ross originates from an explorer of the same name who discovered the seal while leading an Antarctic expedition, and the scientific portion derives from the Greek word for eye (ommato), to mean ‘eyed seal’, owing to the species’ conspicuous large eyes. O. rossii are an elusive seal, but seemingly abundant and widespread, therefore the IUCN considers them Least Concern. Estimated population size = 130,000.
O. rossii are a medium sized true seal (males up to 2.1 m long/ 216 kg, females up to 2.6 m/ 225 kg). Flippers at the rear and front are relatively long and slender, and the fore ones are further forward than they may be on other species. The head is very small but rounded, and they have a blunt little muzzle with a small mouth. Eyes, however, as eluded to in the name, are large and black, reaching up to 7 cm in diameter. The head joins directly to the body with seemingly little to no neck and this gives the overall profile of the seal an almost tapered look, from a point at the nose, widening across the body, to a tapered end at the rear. The coat is usually a dark brown or dark grey in colour with a paler underside, and they have characteristic strips that run down the front of their necks from the head to the chest.
Feeding behaviour:
Studies have indicated that O. rossii may spend months offshore foraging, diving for over 30 minutes at a time, and frequently reaching depths of 100-300 m. They appear to mostly consume squid, and to be a specialist at hunting these, although evidence of fish including icefish, and invertebrates including krill have also been found in stomach analyses. It is thought that when the seals return to land to breed and moult, they may have extended periods of fasting.
Breeding behaviour:
Sexual maturity – males 3-7 years old/ females 3-4 years old.
Mating is presumed to take place underwater, though little is known about this secretive and solitary species. It is thought that like many other pinnipeds, there is a delayed implantation period of 2-3 months after copulation to allow the female to gain and replenish fat from nursing her recent offspring, before the new foetus starts developing. Genetic studies have indicated that O. rossii have a monogamous breeding structure, with females hauling out to give birth on the pack ice in November, and nursing the newborn pups for approximately 4 weeks. The pups, born with a warm, dark brown coat that is buff to yellowish on the underside, are aquatic fairly early on, entering the water and learning to swim whilst they are still drinking milk. The moult for the adult seals takes place in January. O. rossii are known to live for up to 20 years, but being based on only a small sample, this figure may well be higher.
There are no subspecies of O. rossii.

Photo: NOAA

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