The Ross seal (Ommatophoca rossii) is one of nineteen species of marine mammals in the family of True seals. Together with the families of Eared seals and Walruses, True seals form the group of marine mammals known as pinnipeds. The Ross seal is the only member of genus Ommatophoca, which is therefore monotypic.
Ross seal. Source: Collection Georges Declercq
Kingdom: Animalia (Animals)
The Ross seal is the smallest seal within the Antarctic region, with a thick neck and a slender body. Members of this species have abbreviated length body hair, with the shortest hair and vibrissae of any phocid. The species manifests a dark brown colour on the dorsal surface, with a silvery ventral surface; spots and streaks frequently mark the head, neck and flank. During the summer, unmoulted Ross seals are tan to brownish, with moult occurring in January.
Males average dimensions smaller than females, from 168 to 208 centimeters (cm) long and body mass ranging from 129 to 216 kilograms (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 (70 millimeters in diameter). The large eye sockets in the skull are a suitable diagnostic by which a Ross seal can be identified in the field.
Relatively little is known about mating habits of Ross seals. Females become sexually mature at two to four years of age, while males can reproduce initially with attainment of an age of three to four. Ross Seals mate in early December, but implantation is delayed until early March. Pupping season occurs in early November, after a nine month gestation period. A typical male weighs 16.5 kg at birth and nurses for four to six weeks. Weaning is complete around mid-December, approximately six weeks after birth. After 15 days of nursing, pups reach a weight of about 75 kg.
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. </div></div>
Male Ross seals male have been known to reach 21 years, while the oldest female known achieved an age of 19 years.
The Ross seal is thought to be solitary and sparsely distributed across pack ice habitats. Field observations reveal that only three to nine percent of Ross Seal sightings involve a concomitant sighting of a second seal. However, it is thought that O. rossii may be more social than they appear terrestrially, because lone seals on ice are often associated with diving seals beneath the ice surface. In fact, Ross Seals can establish territories underwater through vocalisations.
Distribution and habitat
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. 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
Ross seals are associated with habitat areas of medium to dense pack ice. The areas in which they dwell are often remote and difficult to navigate. This results to a paucity of scientific information regarding the specific habitats they are prone to utilise.
Predators and prey
Prey of the Ross seal can be deciphered from stomach content analysis. Squid beaks and fish remains have been found in the guts of Ross seals. Studies have thus shown the diet to consist of approximately 64% Cephalopoda, 22% fish, and 14% other invertebrates.
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 are estimates, since so much is presently 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; moreover. Ross seals are protected under the Convention for the Conservation of Antarctic Seals.
Economic importance for humans
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 an unlikely potential tourist attraction.
- Ommatophoca rossii Gray, 1844 Encyclopedia of Life (accessed April 17, 2009)
- Ommatophoca rossii, Lundrigan, B. and A. Kamarainen, 2003, Animal Diversity Web (accessed April , 2009)
- Ross Seal, Seal Conservation Society (accessed April 17, 2009)
- Ommatophoca rossii, IUCN Red List of Threatened Species (accessed April 17, 2009)
- The Pinnipeds: Seals, Sea Lions, and Walruses, Marianne Riedman, University of California Press, 1991 ISBN: 0520064984
- Encyclopedia of Marine Mammals, Bernd Wursig, Academic Press, 2002 ISBN: 0125513402
- Marine Mammal Research: Conservation beyond Crisis, edited by John E. Reynolds III, William F. Perrin, Randall R. Reeves, Suzanne Montgomery and Timothy J. Ragen, Johns Hopkins University Press, 2005 ISBN: 0801882559
- Walker's Mammals of the World, Ronald M. Nowak, Johns Hopkins University Press, 1999 ISBN: 0801857899
- Ross Seal, MarineBio.org (accessed April 17, 2009)