The Ross seal (Ommatophoca rossii) is one of four true seal species in Antarctic waters. It remains the least studied, primarily residing in remote, dense pack ice, which makes observation exceptionally difficult. Its secretive nature contributes to its mysterious reputation in one of the planet’s most extreme environments.
Physical Characteristics and Habitat
The Ross seal is comparatively small among Antarctic seals, reaching lengths between 1.68 and 2.09 meters and weighing 129 to 216 kilograms; females are often slightly larger. It has a unique appearance, characterized by a short, wide snout and disproportionately large eyes, up to 7 centimeters in diameter. Its fur is dark brown dorsally and silvery-white ventrally, often adorned with spots or streaks on its head, neck, and flanks. It also has notably short hair and vibrissae compared to other phocids. It can retract its head into its body, giving it a stout appearance.
The species was named after British explorer Sir James Clark Ross, who first described it during his expedition in 1841. Ross seals exhibit a strong preference for the densest, most inaccessible pack ice surrounding the Antarctic continent, making their distribution circumpolar but sparse. Their preference for remote, hard-to-navigate ice explains their infrequent sightings and limited understanding of their habitat use. While primarily restricted to Antarctic seas, rare instances of individuals venturing to subantarctic islands or even off the coast of Australia have been recorded.
Diet and Foraging Behavior
The diet of the Ross seal consists predominantly of cephalopods, particularly squid, which account for approximately 47% of its intake. Fish, such as lanternfish (myctophids) and Antarctic silverfish, make up about 34% of its diet, while crustaceans like Antarctic krill and other invertebrates constitute the remaining 19%. This specialized diet distinguishes the Ross seal ecologically from other Antarctic seals, which often rely more heavily on krill or larger fish.
Ross seals are deep-diving hunters, able to descend to nearly 300 meters (1000 feet) and remain submerged for over 20 minutes, though most dives are shallower and shorter. They spend a considerable amount of time foraging in open water, even while considered ice-dependent. Their large eyes aid their vision in the dim light of deeper waters, assisting in the pursuit of pelagic prey.
Unique Vocalizations and Social Structure
The Ross seal is widely recognized for its distinctive and complex vocalizations, often described as siren-like, trilling, or a combination of chugging and chirping sounds. These sounds can be produced both in and out of the water and are unique because they are emitted with a closed mouth, releasing no air. The calls can travel long distances, potentially several kilometers, a notable trait given the seal’s largely solitary nature.
The exact purpose of these vocalizations remains unclear, but they may serve various functions such as territorial displays, underwater navigation, or long-distance communication between individuals. While typically observed alone or in very small groups, the consistent calling might facilitate encounters or avoidance, especially since they do not form large colonies. Some researchers suggest that these sounds might indicate their presence to other seals that are diving beneath the ice, hinting at a more complex social dynamic than their solitary surface appearances suggest.
Reproduction and Conservation Status
Ross seal pupping typically occurs on the pack ice during November. Females give birth to a single pup, which is nursed for a relatively short period, possibly as brief as 13 days, though historical estimates suggested up to six weeks. Pups are born weighing around 16 to 27 kilograms and measure about 1 to 1.2 meters in length. Mating likely happens underwater shortly after the pups are weaned, but direct observations are scarce.
The conservation status of the Ross seal is currently listed as “Least Concern” by the IUCN Red List. This designation is largely attributed to its remote and inaccessible habitat within the dense Antarctic pack ice, which historically protected it from extensive commercial hunting and direct human disturbance. While the total population estimate is uncertain, with figures ranging from 20,000 to 227,000, genetic studies do not indicate a recent, significant decline. The primary long-term concern for the Ross seal population is the potential impact of climate change on its pack ice habitat, which could reduce its preferred breeding and foraging grounds.