ORIGINAL PAPER G. J. G. Hofmeyr Æ B. A. Krafft Æ S. P. Kirkman M. N. Bester Æ C. Lydersen Æ K. M. Kovacs Population changes of Antarctic fur seals at Nyrøysa, Bouvetøya Received: 3 November 2004 / Revised: 10 March 2005 / Accepted: 12 March 2005 / Published online: 19 May 2005 Ó Springer-Verlag 2005 Abstract Antarctic fur seal Arctocephalus gazella pup production at Nyrøysa, Bouvetøya was estimated to be approximately 15,000 per annum during each of four summers from 1996 to 2002, indicating a total popula- tion of about 66,000. While the Bouvetøya population is the second largest for this species, pup production at this site still accounts for only 2.4% of the global total. This population experienced a mean annual rate of increase of 30.6% for the period 1989–1996, perhaps due, in part, to significant immigration, but has been stable since 1996. Historical accounts of significant numbers of animals being present towards the end of the period of sealing (C.1800–1930), indicate that the geographic iso- lation and inaccessibility of this site may have resulted in the Bouvetøya population being one of three popula- tions that survived a series of periods of extreme exploitation of this species. Introduction Uncontrolled harvesting of seals in the Southern Ocean during the late Eighteenth and early Nineteenth Centu- ries severely reduced all populations of Antarctic fur seals, Arctocephalus gazella (Bonner 1968). This was followed by a partial recovery in the mid Nineteenth Century. A further period of intensive sealing took place during the 1870s, again bringing partially recovered populations close to extinction (Bonner 1968). Sub- sequent to the cessation of exploitation in the early Twentieth Century, the species has experienced consid- erable population growth (Bonner 1968; Laws 1973; Payne 1977; Boyd 1993; Shaughnessy et al. 1998), and currently numbers well over a million animals (Boyd 1993). Antarctic fur seals have now recolonised many of their former haulout sites and breed at some ten islands or island groups (McCann and Doidge 1987; Boyd 1993). Antarctic fur seals were noted on Bouvetøya (54°25¢S, 3°20¢E) at the time of the island’s discovery in 1739. Harvesting was initiated during the first landing in 1822, when sealers under the command of Capt. Ben- jamin Morrel killed 196 animals. Sealing vessels con- tinued to harvest fur seals during subsequent infrequent visits to the island during the Nineteenth Century (Christensen 1935). The last recorded harvest took place in 1927 (Christensen 1935). The main breeding site at the time was Larsøya, a small offshore island. A few breeding seals were also present at this time on Bou- vetøya itself at Kapp Norvegia (Olstad 1929). Little other suitable breeding space was available since the rest of the coastline consisted of narrow beaches backed by high cliffs. This situation changed in the 1950s when a landslide on the west coast of Bouvetøya created the coastal platform, Nyrøysa (Prestvik and Wisnes 1981). This platform is approximately 2 km long and 500 m wide, and provides extensive breeding space for Ant- arctic fur seals. Nyrøysa has become the main breeding site for the Bouvetøya population. The first assessment of pup production at this site was reported in Holdgate et al. (1968), who estimated that 150–180 pups were present on Nyrøysa in April 1964. Haftorn et al. (1981) counted some 950 pups during the 1978/79 season. The number of pups present had grown to approximately 2,000 by 1990/91 (Bakken 1991). With the inception of a CCAMLR (Commission for the Conservation of Antarctic Marine Living Resources) Environmental Monitoring Programme at Bouvetøya, estimates of fur seal pup production were made during four austral summers from 1996 to 2002. These data are G. J. G. Hofmeyr (&) Æ S. P. Kirkman Æ M. N. Bester Mammal Research Institute, Department of Zoology & Entomology, University of Pretoria, Pretoria, 0002, South Africa E-mail: ghofmeyr@zoology.up.ac.za Tel.: +27-12-4204608 Fax: +27-12-4202534 B. A. Krafft Æ C. Lydersen Æ K. M. Kovacs Norwegian Polar Institute, Polar Environmental Centre, 9296 Tromsø, Norway Polar Biol (2005) 28: 725–731 DOI 10.1007/s00300-005-0732-7