The Weddell seal (Leptonychotes weddellii) is a true seal and one of the largest members of the Phocidae family, with adults measuring 2.5 to 3.5 m (8 ft 2 in–11 ft 6 in) in length and weighing from 400 to 600 kg (880–1,320 lb). The species has a circumpolar distribution around Antarctica. Unlike the three other Antarctic seal species (leopard, crabeater, and Ross seals) that inhabit the broken and circulating pack ice extending northward from the continent into the southern ocean, Weddell seals are associated with the fast ice frozen to the continent. They are predators near the top of the food chain and are exceptional divers, capable of holding their breath for up to an hour and diving to depths up to 600 m. Their primary prey are the herring-like Antarctic silverfish, the large Antarctic toothfish, cephalopods, and a variety of smaller fishes. Leopard seals prey on their pups as do Orcas that also prey on adults.
During the Austral spring, Weddell seals are found in colonies hauled out on the ice in localized areas where cracks due to tides and glacier pressures provide ready access to the ice surface. The females give birth to a single pup and closely attend the pup, with nursing lasting for 30-40 days. Mothers feed very little, if at all, while nursing and lose up to 40% of their body mass. Pups are actively encouraged by mothers to enter the water, with most pups beginning to swim at 10-12 days of age. During the pup-rearing period, adult males establish underwater territories associated with the colonies and compete aggressively to breed females when they become receptive at about the time pups are weaned. Copulation occurs underwater. Maximum life span is approximately 30 years.
Weddell seals are docile when hauled out on the sea ice, with no fear of man, and were exploited for food and fuel during the era of exploration in the late 1800s and early 1900s, with local populations depleted in areas where expeditions were concentrated. All Antarctic seals are currently protected by the international Antarctic Treaty (1961) and the Convention for the Conservation of Antarctic Seals (1978). Weddell seals are the most studied of the Antarctic seal species due to their mild temperament and because researchers have ready access to the animals when the seals are hauled out on the fast ice. The species is considered secure, but there is no reliable estimate of their abundance. Because Weddell seals are closely associated with sea ice and their primary prey are ice-obligates there is concern that global climate change may impact the distribution and abundance of the species in the future. The recent development of commercial fisheries in some portions of the seal’s range also has the potential to impact food resources.
Today, we release the genome assembly for the Weddell seal, Leptonychotes weddellii! The sample used for this experiment was provided by Robert Garrott, Montana State University. Field work for the project was supported by the National Science Foundation, Division of Polar Programs under grant numbers ANT 1141326 and ANT 1640481 to Jay J. Rotella, Robert A. Garrott, and Donald B. Siniff and prior NSF Grants to Robert A. Garrott, Jay J. Rotella, D. B. Siniff, and J. Ward Testa. Browse the 17 chromosomes of the Weddell seal below in the interactive Juicebox.js session below, and visit the assembly page for more data and links.
This is our 7th Phocidae genome assembly, check out the rest here!
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