Ross Seal

Observations: The period of pre-implantation usually takes 3.5 to 4.5 months, increasing the gestation time up to 1 year. In the wild, these animals are believed to live up to 21 years (David Macdonald 1985). Their longevity in captivity has not been studied in detail and hence maximum longevity remains unknown.

Ross seals use vocalizations to communicate with other seals.

Communication Channels: acoustic

Perception Channels: visual ; tactile ; acoustic ; chemical

Ross seals are thought to be the least abundant seal in Antarctica and recent estimates suggest that the population may be approximately 220,000. However, these estimates are little more than guesses since so much is still unknown about Ross seal distribution and behavioral patterns. Exploitation of this rare seal species is not likely due to the remoteness of its preferred habitat, yet Ross seals are protected under the Convention for the Conservation of Antarctic Seals (King 1990).

IUCN Red List of Threatened Species: least concern

Habitat occupied by Ross seals is accessible only by ice breaker or aircraft, therefore they have little direct economic importance. Also, the remote location of their habitat makes them a poor potential tourist attraction.

Aside from their role in healthy Antarctic ecosystems, there is no established positive economic importance for humans.

The role of Ross seals in the ecosystem has not yet been determined, however, they are important predators on fish and cephalopods.

Squid beaks and fish remains have been found in the guts of Ross seals (Skinner 1984). Studies have shown the diet to consist of approximately 64% cephalopods, 22% fish, and 14% other invertebrates (Oritsland 1977).

Animal Foods: fish; mollusks; aquatic crustaceans

Primary Diet: carnivore (Molluscivore )

Ross Seals are unique in that they are the only Antarctic seal whose range is restricted to the Antarctic seas, and they have never been documented in extra-polar regions (Allen 1942). These seals are circumpolar, with most individuals found on the pack ice off the shores of Antarctica, with their range extending no farther than 60° S latitude (King 1990).

Biogeographic Regions: antarctica (Native ); atlantic ocean (Native ); pacific ocean (Native )

Ross seals are associated with areas of medium to dense pack ice (Spettstoesser et al. 2000). The areas in which they dwell are often remote and hard to navigate. This leads to a lack of information about the specific habitats they are prone to utilize. Observational accounts recorded in Spettstoesser et al. (2000) make an initial attempt to determine specific habitat use, however data remain vague and anecdotal.

Habitat Regions: polar ; saltwater or marine

Terrestrial Biomes: icecap

Ross seal males have been known to reach 21 years, while the oldest female known was 19 years old (King 1990).

Range lifespan
Status: wild: 21 (high) years.

Ross seals are the smallest seals of the Antarctic region, with a thick neck and a slender body. Members of this species have short body hairs, with the shortest hair and vibrissae of any phocid. They are dark brown on their dorsal surface and their ventral surface is silvery; spots and streaks frequently mark the head, neck, and flank. During the summer, unmoulted seals are tan to brownish, with moult occurring in January. Males average smaller than females, from 168 to 208 cm long and weighting 129 to 216 kg. Females measure from 190 to 250 cm long and weigh between 159 and 204 kg. Ross seals can easily be distinguished from closely related seals by their disproportionately large eyes (70mm in diameter). The large eye sockets in the skull are a good character by which a Ross seal can be identified (King 1990).

Range mass: 150 to 215 kg.

Range length: 168 to 250 cm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: female larger

Ross seals are thought to have no predators since typical seal predators, such as killer whales and leopard seals, are rarely found in habitats utilized by Ross seals (Skinner 1984).

Little is known about mating in Ross seals.

Females become sexually mature at 2 to 4 years of age, while males can reproduce for the first time between ages 3 and 4. Ross seals mate in early December, but implantation is delayed until early March. Pupping season occurs in early November, after a 9 month gestation period. A typical male weighs 16.5 kg at birth and nurses for 4 to 6 weeks. Weaning is complete around mid-December, approximately 6 weeks after birth (Skinner 1984). After 15 days of nursing pups reach a weight of about 75 kg.

Breeding season: Breeding occurs in December, pups are born in early November.

Average number of offspring: 1.

Average gestation period: 9 months.

Range weaning age: 4 to 6 weeks.

Range age at sexual or reproductive maturity (female): 2 to 4 years.

Range age at sexual or reproductive maturity (male): 2 to 4 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (Internal ); viviparous ; delayed implantation

Average birth mass: 20000 g.

Average gestation period: 228 days.

Average number of offspring: 1.

Young Ross seals develop quickly once born, gaining weight rapidly from their mother's rich milk. Once they are weaned they become independent from their mother.

Parental Investment: precocial ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female); pre-weaning/fledging (Provisioning: Female)

The Ross seal was described during James Clark Ross' British Antarctic Expedition in 1841,lives on and around the pack ice of Antarctica. The seal has a circumpolar distribution in the Southern Ocean surrounding Antarctica, with individuals found in low densities - usually singly - in areas of medium to dense, consolidated pack ice in all regions of the continent in summer, when the seals haul out to breed, moult and rest (10). The seal almost never leaves the Antarctic Ocean; stray animals are occasionally found around sub-Antarctic islands and off the south coast of Australia (8,9). It may move north to the open ocean in autumn (7). The male is 168-209 cm long and weighs 129-216 kg; females are slightly larger at 190-250 cm long and weighing 159-204 kg. The seal has disproportionately large eyes, up to 7 cm in diameter; Ommato- means "eye" and phoca means "seal". It has a thick neck and slender body with the shortest hair and whiskers of any seal. The coat is dark-brown in the dorsal area and silvery-white beneath; spots and streaks frequently mark the head, neck, and flank. In summer, unmoulted seals are tan to brownish, with the moult occurring in January. At the onset of winter, the coat fades gradually to become light brown. Moulting probably occurs in January, when many Ross seals seem to fast (6). In summer most Ross seals are hauled out on the ice at midday (11-13). Some seals may move north to the open ocean in autumn (7). When a female was in the water, she dived continuously with dives averaging 110 m deep and 6.4 minutes long, with a maximum of 212 m and up to 9.8 minutes. The dives were deepest at twilight and shallowest at night and it hauled out by day (13). Ross seals are usually found singly on the ice. The seal can produce a variety of complex twittering, trilling and siren-like sounds on ice and underwater; these can carry for long distances (4). The underwater siren sound can be composed of two harmonically unrelated superimposed tones that are pulsed with the same rhythm. The vocalizations, whether on ice or in water, are made with a closed mouth - emitting no air. Their distinctive nature and long range are likely to facilitate encounters or avoidance of individuals (4). The Ross seal feeds primarily on squid and fish, primarily Antarctic silverfish, in the pelagic zone (6,14,15), but it also eats other invertebrates including some krill (11). Seals may fast during the post-breeding moulting period. Their predators probably include killer whales and leopard seals , but these are rarely found in habitats utilized by Ross seals (14). The seals probably mate in the water in early December, soon after the pup is weaned. Females give birth to their precocial young on the ice in early November, with a peak from early to mid-November (12). The period of pre-implantation usually takes 3.5 to 4.5 months, increasing the gestation time up to 1 year; the usual gestation is @ 9 months. Pups are @ 100-139 cm long and weigh @ 16-20 kg at birth, with some males weighting 16.5 kg. They develop quickly, gaining weight rapidly from their mother's rich milk. After 15 days of nursing pups weigh @ 75 kg. They are nursed for 4-6 weeks before weaning around mid-December (14), when the pups become independent. Nursing pups may swim between ice floes. The seals mature sexually at about 2-4 years old for females and 2-7 years for males; males reproduce for the first time at 3-4 years old. The average age of reproducing seals should be at least 10 years old. The seal reaches physical maturity at @ 9 years and is thought to live around 20 years in the wild (6,16); the oldest known male was 21 years old and the oldest female known was 19 years old (10). The Ross seal shares a recent common ancestor with the other Antarctic lobodontine seals (tribe Lobodontini): the crabeater, leopard and Weddell seals (2). These species 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 sister clade, Mirounga (elephant seals) in the late Miocene to early Pliocene, when they migrated southward and diversified rapidly in relative isolation around Antarctica (2). The only fossil Ross seals known date from the early Pleistocene of New Zealand (3) The total Ross seal population is estimated at around 130,000 individuals, but reported 95% confidence intervals range from 20,000 to 227,000 (5). The seal has had limited interactions with humans, including being collected for scientific collections. Its range does not generally overlap with commercial fishing. The Red List Category is Least Concern due to the seal's widespread occurrence and large population size (1). A population reduction could occur if sea ice habitats decline due to continued climate warming (17). Ross seals are protected under the Convention for the Conservation of Antarctic Seals

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 seal, crabeater seal, leopard seal, and southern elephant seal), 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.

Breeding is thought to occur from November through December. When hauledout, 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. IUCN: Insufficiently known.

The Ross seal (Ommatophoca rossii) is a true seal (family Phocidae) with a range confined entirely to the pack ice of Antarctica. It is the only species of the genus Ommatophoca. First described during the Ross 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", and phoca meaning "seal"), and complex, trilling and siren-like vocalizations. Ross seals are brachycephalic, as they have a short broad muzzle and have shorter fur than any other seal.

circumpolar in the Antarctic

in pack ice areas