Scientific Name: Leptonychotes weddellii (Lesson, 1826)
English – Weddell Seal
Otaria weddellii Lesson, 1826
Taxonomic Notes: Rice (1998) notes that the specific name was frequently misspelled (weddelli) prior to Bonner (1988).
Assessment Information [top]
Red List Category & Criteria: Least Concern ver 3.1
Year Published: 2015
Date Assessed: 2014-12-02
Assessor(s): Hückstädt, L.
Reviewer(s): Boveng, P.
Facilitator/Compiler(s): Lowry, L., Ahonen, H., Pollock, C.M., Chiozza, F. & Battistoni, A.
Due to its widespread occurrence, large population size and lack of major threats, the Weddell Seal is classified by IUCN as Least Concern.
Previously published Red List assessments:
2008 – Least Concern (LC)
1996 – Lower Risk/least concern (LR/lc)
Geographic Range [top]
Circumpolar and widespread in the Southern Ocean, Weddell Seals are the world’s southern-most breeding mammal and occur in large numbers on fast ice, right up to the shoreline of the Antarctic continent. They also occur offshore in the pack ice zone north to the seasonally shifting limits of the Antarctic Convergence. A small population lives all year on South Georgia. Weddell Seals are present at many islands along the Antarctic Peninsula that are seasonally ice-free. Vagrants have been recorded in many areas north of the Antarctic in South America, New Zealand and southern Australia (Kooyman 1981, Rice 1998).
Antarctica; South Georgia and the South Sandwich Islands (South Georgia, South Sandwich Is.)
Argentina; Australia (South Australia); Bouvet Island; Chile (Juan Fernández Is.); Falkland Islands (Malvinas); French Southern Territories (Kerguelen); Heard Island and McDonald Islands; New Zealand (Antipodean Is., North Is.); South Africa; Uruguay
FAO Marine Fishing Areas:
Atlantic – southwest; Atlantic – southeast; Atlantic – Antarctic; Indian Ocean – eastern; Indian Ocean – Antarctic; Pacific – southeast; Pacific – Antarctic; Pacific – southwest
Estimated area of occupancy (AOO) - km2: 21547648 Continuing decline in area of occupancy (AOO): No
Extreme fluctuations in area of occupancy (AOO): No Estimated extent of occurrence (EOO) - km2: 33454727
Continuing decline in extent of occurrence (EOO): No Extreme fluctuations in extent of occurrence (EOO): No
Continuing decline in number of locations: No
Extreme fluctuations in the number of locations: No
Upper elevation limit (metres): 3 Lower depth limit (metres): 600
Range Map: Click here to open the map viewer and explore range.
The global population of Weddell Seals has been variously estimated at 200,000 to 1,000,000 individuals (Erickson and Hanson 1990, Southwell et al. 2012), although there is large uncertainty in these figures. Weddell Seals are a widespread species and population assessments are very difficult and expensive to conduct, and are therefore infrequently undertaken. Southwell et al. (2012) reported on results from the Antarctic Pack-Ice Seals program which conducted extensive surveys during 1996-2001. They estimated 633,000 Weddell Seals in two of their survey sectors. In the third sector fast ice was not surveyed and Weddell Seal abundance was not estimated.
Current Population Trend: Unknown
Number of mature individuals: 300000 Continuing decline of mature individuals: Unknown
Extreme fluctuations: No Population severely fragmented: No
Habitat and Ecology [top]
Habitat and Ecology: Adult male Weddell Seals reach 2.9 m in length, while females reach 3.3 m. Adults in their prime weigh 400-450 kg, with females being somewhat heavier than males, sometimes reaching over 500 kg (Stirling 1971). Adult female weight fluctuates dramatically during the year with significant weight loss occurring after birth and during lactation. Newborns are about 1.5 m long and average 29 kg. Females become mature at three to six years of age and males at seven to eight years. The annual pregnancy rate of mature females is 70-80%. Gestation lasts 11 months, including a delay of implantation of two months. Longevity is approximately 25 years (Stirling 1971, Reijnders et al. 1990).
Weddell Seals breed in areas of predictable stable fast ice or on land, allowing them to form loose aggregations (or breeding colonies) at specific sites (Siniff 1981, Testa et al. 1990). Weddell Seal pups are born from October through November. Adult females nurse their pups for a prolonged period (seven to eight weeks), and although they fast during the first one to two weeks, adult females do forage during lactation (Stirling 1971). Pups are born earlier at lower latitudes than at higher latitudes (Testa et al. 1990). Females enter oestrus approximately one week before weaning their pup, and copulation occurs underwater, where males maintain territories by controlling access to breathing holes and cracks. Adult Weddell Seals display strong site fidelity, with both males and females returning to the same breeding colony. When in the shore-fast ice habitat, Weddell Seals tend to congregate in loose groups along recurrent cracks, leads, and near access holes to the water (Siniff 1981). The behaviour of animals breeding in the pack ice or in the Sub-Antarctic islands is not well known.
Satellite data on movement patterns of Weddell Seals have increased during the last decade, providing a clearer picture of their distribution patterns. Weddell Seals habitat utilization and habitat patterns vary largely at a regional scale, showing large differences in the scale of their movements (tens to hundreds of km) depending on the area they inhabit (K. T. Goetz pers. comm., Heerah et al. 2013). Further, there seems to be large individual variability in their patterns of habitat usage, with some individuals staying in close proximity to their breeding colonies (e.g., McMurdo Sound), whereas others venture into the pack ice, likely exploiting polynyas and areas of thinner sea ice. The data available on newly weaned and subadult animals seem to indicate that younger animals move north from the continent and spend the winter in the pack ice.
The diving behaviour of Weddell Seals has been well studied, particularly at McMurdo Sound. They can reach depths of over 600 m, and can undertake dives of at least 82 minutes, feeding primarily feed at depths of 100–350 m, with a diurnal feeding pattern (Testa 1994). Weddell Seals are generalist predators, and their diet likely varies at a regional scale. Their diet primarily consists of notothenoid fish (Icefishes), particularly the Antarctic Silverfish which largely dominates in the diet in certain areas (Burns et al. 1998), but also includes Antarctic Toothfish, Myctophids and Cephalopods. Although Weddell Seals in fast ice areas are relatively protected, animals in the pack ice are vulnerable to predation by Killer Whales and Leopard Seals (Stirling 1969a, Visser et al. 2008).
Weddell Seals that remain in fast ice areas abrade and grind the ice to maintain access to and from the water. They bite at the ice and then rapidly swing the head from side to side to grind away the ice with their teeth (Stirling 1969ab). Such behaviour, though, comes at a cost, as Seals living in areas where extensive grinding of ice is necessary have accelerated wearing down of their teeth and decreased life expectancy (Stirling 1969b).
Systems: Terrestrial; Marine
Continuing decline in area, extent and/or quality of habitat: No
Generation Length (years): 10.8
Movement patterns: Not a Migrant
Congregatory: Congregatory (and dispersive)
Use and Trade [top]
Use and Trade: Weddell Seals served as an important source of food for men and dogs throughout the early periods of Antarctic exploration (Stirling 1971) until the final removal of dogs from the continent in the 1990s. Local populations no doubt suffered declines from these harvests, but the Murdo Sound population has recovered in the 30 years since harvests ended in the 1980s (Testa and Siniff 1987).
Major Threat(s): At present, there are no immediate or significant threats to the Weddell Seal.
The potential effects of global climate change on Antarctic seals are largely unknown. Sea ice provides habitat used for pupping, resting, avoidance of predators and access to preferred foraging areas. Learmonth et al. (2006) suggest that Weddell Seal numbers may decline with increasing temperatures if Antarctic sea ice is significantly reduced. In contrast, Proffit et al. (2007), reported that the localized cooling and increased sea ice extent in the Ross Sea was associated with decreased reproduction and lower weaning mass of Weddell Seals in McMurdo Sound. Further, the fact that some populations breed on land (e.g., at South Georgia), could demonstrate an ability in the species to colonize different environments, although the extent of such plasticity is uncertain. Thus, the overall effects of global climate change on Weddell Seals are unknown.
Seasonal tourism in the Antarctic and Sub-Antarctic has increased steadily in the last 30 plus years, and is currently at all-time high levels. The effects of increased vessel noise, disturbance from vessels passage, and close approach by people in small boats and on land or ice, on Weddell Seal behaviour, distribution and foraging are unknown. There is also a risk of injury to a small number of animals from collision with boats or crushing from large vessel passage through ice fields. Currently there are no reports of significant fisheries interactions. However, the development of new fisheries in Antarctic waters, particularly one targeting the Antarctic Toothfish, could have an impact on Weddell Seal nutrition, and potential operational interactions should be considered in the management plans.
Conservation Actions [top]
The Weddell Seal is not listed as endangered or threatened under any national Red List. They are protected by the Antarctic Treaty and the Convention for the Conservation of Antarctic Seals, and any future commercial harvest would be regulated by those international agreements.