(Gray, 1844) - Ross seal
Ross seals are poorly known. They are the smallest of the Antarctic phocids. The head is relatively wide and short. The muzzle is likewise short, wide, and comes to a blunt end. The small number of short, slender vibrissae are possibly the shortest of any pinniped. The eyes are set widely apart and are average in size, despite the huge orbits in the skull. The throat and neck are quite thick, but the rest of the body is of average build for a phocid. The coat is the shortest of any phocid. The hindflippers are very long, just over one-fifth of the standard length.
Ross seals are typically countershaded, dark grey above, blending along the sides, and becoming silvery below. Most striking are the beautiful brown to reddish brown streaks, unique to this pinniped, extending parallel to the long axis 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. Ross seals may have something like an epidermal moult that involves shedding small pieces of skin. Small scars are often seen on the neck, possibly from intraspecific fighting, and some adults bear larger scars, probably from leopard seal or killer whale attacks.
The dental formula is I 2/2, C 1/1, PC 5/5.
Can be confused with
Of the 4 other phocids that share the Ross seal's range (Weddell, crabeater, leopard, and southern elephant seals), the Weddell is most similar in appearance. However, Ross seals are much smaller and have a wider head, and relatively thicker neck (with streaks). Ross seals also tend to be found deeper into the thick pack ice than any other Antarctic phocid.
Based on a small sample of measured animals, Ross seals reach at least 2.4 m and 204 kg. Females are slighlty larger than males. It is estimated that newborn pups are about 1 m and 16 kg.
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.
Biology and Behaviour
Breeding is thought to occur from November through December. 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. However, during the period of the moult, they may be out of the water for longer periods.
Few behaviours have been noted, except for the interesting habit of raising up the head and neck when approached by a human. The seal either stays on its belly or rolls onto its side, keeping the belly towards the person. In this “singing” posture, it opens the mouth to produce trilling, siren-like calls, or chugging vocalizations.
Little is known of the activities of Ross seals in the water, although recent work has revealed that dives average 100 m and 6 minutes. The diet of Ross seals consists primarily of cephalopods, but also includes fishes and krill in some areas.
Ross seals have never been the target of anything but small scale and incidental sealing. Very few have ever been taken for research, and they are poorly represented in scientific collections. This is arguably the most inaccessible seal to humans, and explains the limited exploitation and paucity of knowledge available.