The terrestrial environment of Signy Island, South Orkney Islands, maritime Antarctic, is undergoing rapid and possibly irreversible change caused by a natural biological agent. During the past decade there has been a dramatic increase in the number of Antarctic fur seals Arctocephalus gazella coming ashore on the island during the short summers. It is not known whether significant numbers of seals were present on the island prior to the initiation of commercial hunting in the early 1820s. The impact that the continuing increase of these seals had made on the island's terrestrial and freshwater environments has been sudden and locally devastating. The fragile cryptogam-dominated vegetation has suffered physical damage from which it may be impossible to recover. These seals are also frequenting several of the island's freshtwater lakes which are becoming increasingly eutrophic. The long-term implications of this impact are causing serious concern for the future of the lowland terrestrial and freshwater ecosystems on Signy Island if the fur seal population continues to increase
Abstract:
The fish diet (45% of total diet by weight) of Wandering Albatrosses rearing chicks at South Georgia during the austral winters of 1983 and 1984 was investigated using otoliths retrieved from regurgitations. These provide the first quantitative data for this species and for any albatross. By number of identified otoliths (32% could be identified only as ?Macrouridae and ?Moridae), Pseudochaenichthys georgianus (35%), Muraenolepis microps (33 %) and Chaenocephalus acemtus (20%) predominated, with Notothenia gibberifrons, Pagothenia hansoni and Champsocephalus gunnari (together 12%) also present. Composition by weight (estimated from otolith length) of the main species was Pseudochaenichthys 51%, Muraenolepis 14%, Chaenocephalus 27%; if digestion and wear had reduced otoliths by 10% the values would be Pseudochaenichthys 54%, Chaenocephalus 25%, Muraenolepis 13%. Com- position by weight (actual or corrected values) was almost identical between years but epipelagic fish were significantly more abundant in +I983 than 1984. All identified fish eaten by Wandering Albatrosses are common on the South Georgia continental shelf and most of them are caught in the commercial fishery there. However, two of the three main target species of this fishery in 1983 - 1984, Notothenia rossii and Champsocephalus were not, or rarely, caught by Wandering Albatrosses. It seems unlikely, therefore, that the albatrosses depend . greatly on the fishery for acquisition of fish prey but how they catch several species, including Muraenolepis, which are mainly benthic in habit is unknown.
