Population size and trends within the two populations of Southern Buller's Albatross Diomedea bulleri bulleri P.M. Sagar a, *, J.C. Stahl b , J. Molloy c , G.A. Taylor c , A.J.D. Tennyson b a National Institute of Water and Atmospheric Research, PO Box 8602, Christchurch, New Zealand b Museum of New Zealand Te Papa Tongarewa, PO Box 467, Wellington, New Zealand c Biodiversity Recovery Unit, Department of Conservation, PO Box 10420, Wellington, New Zealand Received 7 July 1998; received in revised form 7 October 1998; accepted 15 October 1998 Abstract The abundance and distribution of Southern Buller's Albatross (Diomedea bulleri bulleri) were investigated at the Solander Islands in February 1996 and at The Snares in March 1997. The total breeding population of this endemic subspecies was estimated at 11 502 breeding pairs. At the Solander Islands, a total of 2625 occupied nests was estimated from aerial and ground counts in the ®rst accurate census that included all islands in the group. Comparisons with the number of chicks counted on Little Solander Island in 1985 indicated a possible decrease of 18.7% or no change in the numbers of breeding pairs during the period 1985±1996. At The Snares, a total of 8242 occupied nests was counted and a further 635 were estimated on North East Island, Broughton Island, and associated islets and stacks. A comparison with the numbers of occupied nests counted on North East Island, The Snares, during 1969 and 1992 indicated population increases of 78% and 8% during the periods 1969±1992 and 1992±1997, respec- tively. Dierences in the rates of change within The Snares population demonstrate the complexity of population parameters within a single seabird species, thus emphasising the need for careful formulation of conservation measures. # 1999 Elsevier Science Ltd. All rights reserved. Keywords: Southern Buller's Albatross; Diomedea bulleri; Solander Islands; The Snares; Population status 1. Introduction There are 14 extant species of albatross worldwide; ten are con®ned to the Southern Ocean, three to the North Paci®c, and one to the tropics (Warham, 1990). In recent decades, factors in¯uencing albatross survival have changed markedly, particularly as a result of a dramatic rise in commercial ®shing operations (Gales, 1993). These operations have both bene®cial and detri- mental eects on albatrosses. For example, Black- browed Albatrosses (Diomedea melanophrys) breeding at the Falkland Islands have been shown to obtain about 15% of the food fed to chicks as oal discharged from the squid trawl ®shery (Thompson, 1992). In con- trast, incidental mortality as a result of longline opera- tions is thought to have been a major contributing factor in the declines of Wandering Albatross (D. exulans) (Weimerskirch and Jouventin, 1987; Croxall et al., 1990; Weimerskirch et al., 1997) and Grey-headed Albatross (D. chrysostoma) (Prince et al., 1994) populations. In the New Zealand region, albatross mortality has been documented for the hoki (Macruronus novaeze- landiae) trawl (Bartle, 1991), squid trawl (Bartle, 1991), and southern blue®n tuna (Thunnus maccoyii) longline (Murray et al., 1993) ®sheries. Southern Buller's Alba- tross (D. bulleri bulleri) is one of the species most fre- quently reported of the endemic New Zealand albatrosses in this incidental mortality. Southern Bul- ler's Albatrosses are endemic to New Zealand, where breeding colonies are con®ned to the Solander Islands and The Snares. The ®rst estimates of the breeding population at the Solander Islands were 2000 pairs (Robertson, 1985) and 4300 to 5300 pairs from an aerial survey (Cooper et al., 1986). However, neither estimate is based on empirical data (C.J.R. Robertson and C.M. Miskelly, pers. comms.). At The Snares, counts of nesting albatrosses were completed in February 1969 (Warham and Bennington, 1983) and March 1992 (Sagar et al., 1994), when 4750 and 8460 pairs were estimated, respectively. In a review of the past and present population 0006-3207/99/$Ðsee front matter # 1999 Elsevier Science Ltd. All rights reserved. PII: S0006-3207(98)00129-3 Biological Conservation 89 (1999) 11±19 * Corresponding author. Tel.: +64-3-348-8987; fax: +64-3-348- 5548; e-mail: p.sagar@niwa.cri.nz