Ross seals are typically countershaded, dark above, blending along the sides, to lighter below. The dark coloration is described as ranging from dark brown to dark gray and black. Most striking are a series of brown to reddish brown streaks, unique to this pinniped, extending from the face and lower jaw parallel to each other and following the long axis of the back posteriorally along the neck, chest, and sides. The face may appear masked, as a result of the merging of streaks at the eyes and on the lower jaw. There may also be spots, particularly on the sides, where the dark coloration of the back merges with the light color of the undersides.
Coloration becomes duller with more brown and tan tones in late summer before the molt. The epidermal molt occurs in January and possibly February, and involves shedding small pieces of skin with the fur. Scars are often seen on the neck, possibly from intraspecific fighting, and a small percentage of animals have scars from wounds believed to be from leopard seal or killer whale attacks. Pups are born in a two-toned lanugo that is dark brown to blackish above and lighter gray, yellowish to silver below.
The head and neck are thick and wide, while the rest of the body appears proportionately short and slender. The muzzle and mouth are short, giving the end of the head a blunt appearance, and the vibrissae are sparse, short, and inconspicuous. While the eyes are proportionately larger than in any other seal, they appear smallish due to the thick head and neck.
The fore flippers are proportionately long, with short claws as is typical of all four Antarctic phocid species. The first phalange is very long and robust and the rest of the digits are successively shorter, the length tapering rapidly to create a pointed flipper that is similar in profile to the fore flipper of a sea lion. The rear flippers are long, to 1/5 or more of the standard length and are proportionately the longest of any phocid seal. The first and fifth digits of the hind flippers are very long, and much thicker than the other digits.
When disturbed, Ross seals lift their head and neck to the position of the fore flippers, and point the muzzle skyward in a characteristic and unique pose. This position is also used for in air vocalizations.
At maturity, Ross seals are the smallest of the four Antarctic phocids. Based on a small sample of measured animals, Ross seals reach at least 2.4 m and 204 kg. Females are slightly larger than males. It is estimated that pups are about 1 m and 16 kg at birth.
The dental formula is I 2/2, C 1/1, PC 5/5.
Can be Confused With
Of the four other phocids that share the Ross seal's range: Weddell, crabeater, leopard, and southern elephant seals, the Weddell is most similar in appearance. When compared to Weddell seals, Ross seals are shorter, and much smaller in the torso, but have a proportionately wider neck and head, and have streaks on the side of the neck and body. Ross seals also tend to be found in more highly concentrated pack ice than any other Antarctic phocid.
Ross seals have a circumpolar distribution in the Antarctic. They are usually found in dense consolidated pack ice, but can also be found on smooth ice floes in more open areas. Results of recent tagging efforts have revealed that Ross seals migrate north out of the pack ice zone into open water for extended periods of time to forage. Vagrants have been reported from Kerguelen, Heard Island, and South Australia.
Ecology and Behavior
Pups are born in November and December, with a peak from early to mid-November. Weaning takes place at about one month, although little is known of the relationship between mother and pup. Nursing-age pups have been seen swimming between ice floes. Mating is thought to occur in the water, but has not been observed. When hauled-out, Ross seals are generally encountered alone. Occasionally, a small number of individuals may be found in the same area, but they are usually widely-spaced. They may haul-out more from morning to late afternoon. During the period of the molt, they may be out of the water for longer periods.
Few behaviors have been noted, except for the interesting habit of raising up the head and neck and opening the mouth when approached by a human. This has been described as the “singing posture,” but seems to more often serve as an aggressive or defensive posture, from which chugging and trill vocalizations are produced when an animal is approached. Vocalizations are also made from other positions, and while they are in the water, and the species’ repertoire includes many calls that have been variously described to include pulsed chugs, clucks, loud cries, trills, and tonal siren calls.
Little is known of the activities of Ross seals in the water, although recent work has revealed that dives average 100 m in depth and 6 minutes in duration.
Feeding and Prey
The diet of Ross seals consists primarily of cephalopods, but also includes fish and krill.
Threats and Status
Ross seals typically haul-out in dense consolidated pack ice, and can usually only be reached by ice breakers. Small numbers have been collected for commercial purposes, and scientific studies and museums, but otherwise interactions with humans have been few. Ross seals are protected by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals. When wandering outside the pack ice zone, they could come in contact with commercial fishing operations, but there are no reports of interactions to date.