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Pelagic Antarctic krill dominate the invertebrate community in the seas around South Georgia; these small shrimp-like crustaceans feed on the abundant phytoplankton, in turn, they form the diet of many of South Georgia's whales, squid, fish, seals and sea birds. The abundance of krill may be linked to average annual temperatures and the dynamics of the southern ocean currents. Warmer winters result in less sea ice development and in turn low krill abundance.
The bottom dwelling community include particle-feeding organisms such as sponges, tubeworms and molluscs. Predatory groups such as starfish, brittle-stars and sea urchins together with populations of crabs are found around the island. Demersal fish in the main belong to the Notothenioidei group, a perch-type fish living on the continental shelf around the island. These include icefish with no hemoglobin in their blood, rock cods and the larger Patagonian toothfish.
In the early 1900s, whales (blue, fin, sei, humpback and southern right whales) were abundant in South Georgia's waters during the austral summers feeding on the large quantities of krill found on the edge of the island's continental shelf. Intensive commercial hunting of whales removed hundreds of thousands of whales in 60 years and reduced the Southern Ocean stock, once the largest in the world, to less than 10 % of their original numbers and some species to less than 1%. (see graph below)
The International whaling Convention agreed protection of the few remaining species in the Southern Ocean in 1974. GSGSSI's legislation protects marine mammals within South Georgia's waters and thus it can be viewed as a whale sanctuary. Some whales are now seen close inshore as they make a slow recovery in particular southern right whales and humpbacks have been seen in Cumberland Bay and large groups of fin whales have been seen feeding off Shag Rocks. Sightings of the large blue whales remain infrequent. Pods of sperm and killer whales are seen, interacting with the longline fisheries. They can strip Patagonian toothfish off the long line before it is hauled on deck. The southern bottlenose whale, long finned pilot whales and hourglass dolphins also frequent South Georgia's waters.
To view a plot of cetacean sightings at South Georgia from 1991 click here. The sightings came from records at South Georgia Museum.
The plot was prepared by Jessica Richardson of Duke University in collaboration with Woods Hole Oceanographic Institution. Details of a paper published on the whale research from South Georgia Museum and Bird Island records can be found in the last article here.
Seals & Sealing:
Four species of seal are seen regularly at South Georgia. Both the southern elephant seal and Antarctic fur seal breed in significant numbers on the island's beaches. A small colony of Weddell seals breed in Larsen Harbour, Drygalski fjord. Leopard seals can be seen all year around, particularly in winter. The sealing industry from the late 1700s had a significant impact on both the southern elephant seal and the Antarctic Fur seal.
The southern elephant seal was taken for oil; a large male of about 6m can weigh 4,000kg. In 1909 the elephant seal industry on South Georgia, where around 54% of the world's population of southern elephant seals breed, was regulated to avoid excessive population loss. (see graph) The southern elephant seal breed from September to December. Territorial males can defend a harem of up to 100 females. Females stay with their pup for a 28 days lactation period and mate during this period. Adults return to sea to return later in the austral summer to moult.
The hunting of the Antarctic fur seal, taken for its fur, was unregulated and by the early 1900 the species was close to extinction. Since then the species has made a remarkable recovery with over 3 million breeding fur seals now on South Georgia. (see graph). The Antarctic fur seal pup between November and December with the peak of births in December. Mature males (7 to 13 years of age) establish territories on the beaches before the females arrive ashore in a male's territory to pup and then mate.