Weddell seal Leptonychotes weddellii

The Weddell seal Leptonychotes weddellii commonly occurs on fast ice and nearshore pack ice along the Antarctic coast and Peninsula and in small populations in the South Shetland Islands, South Orkney Islands, and South Georgia Island [7,8,9,10]. Wandering Weddell seals have been sighted in the Falkland Islands, Argentina, Uruguay, Chile, Juan Fernandex Island, Bouvet Island, Marion Island, Kerguelen Island, Heard Island, Macquarie Island, Auckland Islands, New Zealand, and southern Australia, [7,8,9,10]. The McMurdo diver will see them around sea ice cracks. The Weddell seal can be over three meters in length and 400 - 450 kilograms in weight. Its population is estimated at 800,000 individuals. Weddell seals move around the sea ice, are not gregarious, and are spaced apart when seen hauled out on the sea ice. Weddell seals are commonly found at 8 - 12 years of age with individuals 18 and 22 years old noted in the literature. Half or more of the Weddell seal diet is fish (Dissostichus mawsoni, Notothenia, Trematomus, Gymnodraco including G. acuticeps, Pleuragramma antarcticum, Cryodraco antarcticus, Pagetopsis macropterus) with the rest being cephalopods (squid and Pareledone octopus), krill, mysids, isopods, amphipods, and decapods [3,4]. Weddell seals hunt fish in the slushy platelet ice on the underside of the sea ice ceiling, by blowing out air to flush fish from their refuge; they hunt the Antarctic cod Dissostichus mawsoni in midwater by silhouetting it against the sea ice ceiling while remaining hidden from sight [12]. Due to the Weddell seal's preference for fast sea ice, the impact of predators such as leopard seals upon the Weddell seal population is minimal.

The Weddell seal dives beneath stable contiguous sea ice and can store a large amount of oxygen in their bodies mostly in their blood and muscles. This enables them to stay underwater for a usual dive to 300-400 meters for fifteen minutes [5]. Weddell seals have been observed staying underwater for 82 minutes and diving down to 700 meters [5]. Weddell seals glide a lot in deep dives rather than swim continuously [2]. The lungs of the Weddell seal collapse during a dive from water pressure thus decreasing the seal's buoyancy on descent [2]. The Weddell seals' limited oxygen storage is thus conserved by taking advantage of this physical change during a deep dive and reducing the amount of swimming during deep dives looking for fish [2]. After several dives, they can be observed coughing up a foamy white lung surfactant [6]. Their underwater swimming speed is estimated at 4- 7 knots [5].


The Weddell seal keeps breathing and entry/exit ice holes open year round using its teeth. Shown here at Granite Harbor are holes running along a sea ice crack that are being kept open by Weddell seals, for their use getting in and out of the water, as well as breathing while in the water. The inner edges of the ice crack would ordinarily run straight, but the Weddell seals round out holes in the crack using their teeth.


The strong upper teeth of the Weddell seal project forward and are dragged from side to side on the edge of an ice hole to keep it open. These teeth may be critical to survival. As the seal ages and its teeth wear down, they seals may lose their ability to maintain breathing holes and die at an earlier age than other seals.

Weddell seals are restless when breathing at a hole when other seals are nearby. They peer down and if a hole fits only one seal, the seal will either dive as another seal comes up or reverse and face down to prevent the intruding seal from surfacing. Weddell seals adopt a head-down fighting posture with eyes looking forward, foreflippers extended and sometimes their jaw open. If a hole is large enough for two seals and the breathing seal refuses to leave, the arriving seal may surface with a fight usually ensuing. It has been suggested that a Weddell seal does not defend an area to the complete exclusion of other seals but to the discouragement of other seals. An intruding seal may be physiologically forced to take a breath which would override territorial aggression.

Here a Weddell sea mother and pup float in shallow water under a sea ice crack; their entry/exit/breathing holes are visible as bright lights above them. Breeding and pupping occur in the summer months. Breeding Weddell sea bulls set up under-ice territories of twenty meters diameter and tend to remain in the water where breeding takes place. Female Weddell seals move freely through the territories of the bulls. Subordinate males have their activity restricted by the dominant bull when moving through a territory. Females claim less well defined territories, individually or jointly with other females. The mother gives birth to her newborn on the sea ice and stays with it for the first twelve days; after that, the mother will spend 30-40% of her time in the water while the pup remains on the sea ice. The pup is born at 29 kilograms and gains 10-15 kilograms per week. By seven weeks of age, the pups can remain submerged for five minutes and dive down to 92 meters. The moulting of the pup's fur is complete in thirty days. The pup nurses for 45 days and, when weaned, the pup weighs 113 kilograms. Weddell seals have high juvenile survival due to a lack of predation in fast sea ice.

The Weddell seal vocalizes underwater and the diver is very aware of their presence even when they cannot be seen. Their calls make an eerie symphony for the diver. Weddell seals produce a wide range of calls: lengthy buzzes descending from a higher pitch to a lower pitch called "trills", whistles, and chirps. Certain vocalizations are associated with aggressive displays and have been characterized as a trill, a rapid chi-chi-chi, an eeeyo, and a chirrup. A teeth clacking sound was observed as seals passed one another entering and leaving breathing holes. A trill is used by mature males to establish and mark their underwater territory; it is associated with tense situations. When a trill isn't heeded, a fight may ensue.

Here's a mother and pup. Weddell seals are highly vocal during the peak of breeding season at the Hutton Cliffs colony; researchers recorded almost twenty underwater calls per minute [1]. In mid-December when mating is almost over, the pups are being weaned, and adults dispersing, the underwater calls of Weddell seals at Hutton Cliffs decreased to two per minute [1]. Why? Their predators, leopard seals and killer whales, showed up at the fast ice edge about twenty kilometers away [1]. Weddell seals are no longer so isolated from their predators by distance from the fast ice edge since the edge shifts south as summer progresses [1]. Killer whales prowl the fast ice edge for prey and leopard seals can swim long distances under ice seeking out Weddell seals and their breathing holes [1]. Leopard seals and killer whales vocalize underwater and Weddell seals hear them [1]. Sounds are important for Weddell seals to communicate with their species but they also need to avoid detection by predators [1]. Absence of sound from Weddell seals is an anti-predation strategy when the risk of predation by leopard seals and killer whales is increased [1].

WAV sound file (886K) of Weddell seals underwater *** click on the ear to listen ***

AU sound file (443K) of Weddell seals underwater *** click on the ear to listen ***

The sonagram below corresponds to this sound file of Weddell seals

Text ©Peter Brueggeman. Photographs ©Rob Robbins & Norbert Wu. Photographs may not be used in any form without the express written permission of Rob Robbins & Norbert Wu. Norbert Wu no longer grants permission for uncompensated use of his photos under any circumstances whatsoever; want more info?