By Omari J. Bayi
Geographic Range
Weddell seals are found throughout the Antarctic continent as well as on fifteen small neighboring islands (Stirling 1971).
Biogeographic Regions:
antarctica 
(native ); oceanic islands (native ); atlantic ocean (native ); pacific ocean (native ).
Habitat
Leptonychotes weddellii live in Antarctic regions on fast ice areas and in the sea. They don't migrate and local movements are caused by changes in ice conditions. Underwater swimming occurs under natural ice cracks or under ice areas thin enough so that the seals can chew breathing holes using canine teeth. Ice areas where these seals dwell are usually flat icy plains (Stirling, 1970).
These animals are found in the following types of habitat:
polar ; saltwater or marine .
Terrestrial Biomes:
icecap.
Physical Description
(880 to 1320 lbs)
(8.2 to 11.48 ft)
Adult Weddell seals have a dark gray coat that is marked with black and lighter gray areas. Males are 2.5 to 2.9 meter in length and females reach up to 3.5 meters. They weigh between 400 and 600 kg.
Some key physical features:
endothermic ; homoiothermic; bilateral symmetry .
Sexual dimorphism: female larger.
Reproduction
In late November to mid-December females are impregnated and about mid-January implantation occurs.
Reproductive behavior occurs underwater. The female is mounted by the male from behind while her sides are held by his foreflippers. Quite often she is bitten on her neck while copulation occurs. Male-male fighting occurs, which suggests that mating systems are polygynous.
Mating systems:
polygynous .
From mid-September to late December active spermatogenesis occurs. In late November to mid-December females are impregnated and about mid-January implantation occurs (Stirling 1971). Gestation last 9 to 10 months. Young pups are born with their permanent dentition. Birth occurs onto the sea ice, which often results in a change of external temperature in newborn pups. Pups are usually born singly, and the time of birth usually varies with latitude from early September at latitude 60 degrees south to late October at latitude 78 degrees south (Stirling 1971). Weddell seal pups weigh about 29 kg at birth. They have a gray lanugo, which after 3 to 4 weeks turns to a dark coat. Weaning takes place at 6 weeks of age and maturity at 3 years. First breeding of females may be denied for 1 or 2 years under some population conditions and males usually don't mate until 6 to 8 years of age because of social pressures (Stirling 1971).
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous ; delayed implantation .
Behavior
The majority of the behavior occurs under water during the night. Weddell seals move in slow humping motion on land as well as on ice. They swim at a speed of about 5 to 7 knots, using their fore and hind flippers. Diving has been measured at depths of 600 m, and they can remain under for up to an hour (Stirling 1971). Drinking sea water as well as eating snow helps this seal meet its water consumption requirements. Eating occurs underwater. Fighting consists of continual chest contact, but is ceased when striking of chest, neck, or other areas occurs. Weddell seals sleep in the same position on the stomach or back for hours, but lying on their sides is most common. To maximize the sun's thermal benefits, seals often lie perpendicular to the sun (Stirling 1971). Play fighting occurs commonly with subadults. The nails of the foreflipper are used for grooming the head, neck, upper sides, and chest. Other areas are groomed by rubbing back and forth against the ice.
Key behaviors:
natatorial ; motile ; nomadic ; solitary .
Communication and Perception
The eyes of Leptonychotes weddellii are well developed for low light visibility. This is an adaptive feature of this creature which assists it in locating breathing holes in the ice (Stirling 1971). Vocalization occurs underwater for communication. Overlapped calls are longer than solitary calls, which constitute the varied repertoire of vocal communication in the Weddell seal (Terhume 1994).
Communicates with:
acoustic .
Food Habits
The diet of Leptonychotes weddellii consists of notothenid fishes, squids, and crustaceans, although they have been witnessed attacking Dissostichus mawsoni (Antarctic toothfish) as large as 54 kg in weight (Stirling 1971). These seals can dive up to 600 meters in search of food and are stealthy hunters, able to sneak attack fish from close range. They also use a method of disturbing fish from ice cracks by blowing bubbles into them and preying on the fish that emerge.
Primary Diet:
carnivore (piscivore , molluscivore ).
Animal Foods:
fish; mollusks.
Predation
- orcas (Orca orcinus)
- leopard seals (Hydrurga leptonyx)
Weddell's seals can be preyed on by orcas (Orca orcinus) or, occasionally, leopard seals (Hydrurga leptonyx).
Ecosystem Roles
These seals are heavily infested with worms and often reguritate them as a means of expulsion. The louse, Antarctophthirus ogmorhini, attacks the hind quarters as well as the penile orifice of these seals. Lice also infest subadults.
- louse (Antarctophthirus ogmorhini)
Economic Importance for Humans: Positive
Leptonychotes weddellii are often killed and used as dog food. Their dead bodies are also of benefit to those studying worms and parasite infestation since these occur so often in this species. Study of their vocal abilities has advanced our attempt to communicate with animals, similar to the vocal communication studies performed with dolphins (Terhune 1994).
Other Comments
These seals are named after Sir James Weddell, commander of British sealing expeditions into the sea which is also named after him, the Weddell Sea.
For More Information
Find Leptonychotes weddellii information at
Contributors
Omari J. Bayi (author), University of Michigan.
