Population biology and ecology of albatrosses on Macquarie Island : implications for conservation status

Four species of albatross breed on Macquarie Island, a small subantarctic island located halfway between Australia and Antarctica. Three of these species (Wandering albatrosses (Diomedea exulans), Black-browed albatrosses (Thalassarche melanophrys) and Grey-headed albatrosses (Thalassarche chrysostoma)) are particularly at risk from elevated mortality levels due to the small size of the breeding populations. Wandering albatrosses have the smallest breeding population of approximately ten breeding pairs each year (total breeding population estimated as 19 breeding pairs), followed by Black-browed albatrosses with approximately 40 breeding pairs each year (total breeding population 38-45 pairs) and Grey-headed albatrosses, with 65-75 breeding pairs each year (total breeding population 100-120 breeding pairs). Light-mantled sooty albatrosses (Phoebetria palpebrata) are more abundant on Macquarie Island (total breeding population estimated at 1500-1800 breeding pairs) and this population represents around 5-10% of the global population. Worldwide declines of many albatross populations were documented in the late 1980's and 1990's and in most cases this was attributable to elevated mortality due to interactions with long-line fisheries. Jn response these concerns, and in an attempt to address the paucity of data on albatrosses breeding on Macquarie Island, a long-term study into the four species was initiated in 1994. The main aims of this study were to determine the conservation status of each species on Macquarie Island, identify -long-term population trends and determine the factors responsible for these trends. To achieve these aims three main aspects were investigated: 1) Population dynamics - involving censuses and identification of breeding birds and collation of historical data to examine longer-term population trends and survivorship; 2) Breeding biology - where breeding success, breeding frequency and attendance patterns were investigated and 3) Foraging ecology- involving satellite tracking ofBlack-browed and Greyheaded albatrosses and a more intensive investigation of the provisioning regime of Lightmantled sooty albatrosses using automatic weighing nests and VHF transmitters. Oceanographic data (Chlorophyll A, Sea Surface Temperature and Sea Surface Height Anomaly) were also obtained and utilised in the analyses of trends in breeding success and satellite tracking. This thesis describes and synthesises data collected from 1994 to 2001 (seven field seasons). These data are discussed both in the context of the threat of long-line fishing and also in the global context. Macquarie Island is the only Australian breeding site of these four albatross species and prior to the current study very limited information was available on these breeding populations. The current study enabled comparisons to be made with other breeding populations of these species at other subantarctic locations (e.g. Iles Crozet and Kerguelen, South Georgia, New Zealand and Marion Island) where long-term studies of these species and close conspecifics have been conducted. The entire breeding populations of the Wandering, Black-browed and Grey-headed albatrosses on Macquarie Island were monitored each year, while a sub-sample of the Lightmantled sooty albatrosses was investigated. All breeding populations were relatively stable between 1994/95 and 2000/01. Prior to this, Wandering albatrosses showed the most variation in both breeding numbers and survivorship. This population was nearly extirpated by 'sealers' at the turn of the century and following their departure from Macquarie Island, breeding numbers slowly increased to peak in the mid 1960's at around 45-50 breeding pairs . .-i Following this increase, breeding numbers started to decline again, reaching a low of 2-3 breeding pairs in the mid-1980's and slowly rising to its current level of 19 breeding pairs in the mid-1990's. The major decline from the 1960's to the 1980's was largely attributable to a sharp decrease in fledgling survivorship and low adult survivorship. These survivorship declines coincided with the advent and proliferation of long-line fisheries, particularly in the Indian Ocean. The Black-browed and Grey-headed albatross breeding populations appeared relatively stable between the late 1970's and the advent of the current study, with some evidence of an increase in breeding numbers. Survivorship of these two species did not vary significantly over this time period. There are limited data on breeding numbers of these two species prior to the 1970's; however a small Black-browed breeding population in the north of the island did decline significantly throughout the 1960's and 1970's and was extinct by the early 1980's. Between 1994/95 and 2000/01 Wandering albatrosses had the highest and most variable breeding success of all albatrosses on Macquarie Island (59.7 ± 6.9 (s.e) %) followed by Grey-headed albatrosses (55.3 ± 4.0 %), Light-mantled sooty albatrosses (50.8 ± 1.9 %) and Black-browed albatrosses (46.1 ± 3.6 %). Chick mortality was generally low for all species, and most variation in overall breeding success could be attributed to variation in hatching success. The inter-annual variation in breeding success of Black-browed albatrosses was correlated with chlorophyll A levels, breeding success of Light-mantled sooty albatrosses was correlated with sea surface temperature and the breeding success of Grey-headed albatrosses was correlated with the intensity and location of sea surface height anomalies. Breeding birds were also classified into 'top' (successful > 65% breeding attempts) and 'bottom' breeders (successful < 35% breeding attempts) and used to further examine variation in breeding frequency and attendance patterns. The breeding frequencies of albatrosses on Macquarie Island are consistent with those found in other studies on the same species breeding at different locations. Wandering albatrosses showed the strictest adherence to the biennial pattern and most Grey-headed and Lightmantled sooty albatrosses also followed this pattern of breeding frequency. Approximately 16-20% of the successful breeders from the latter two species deferred breeding for more than two years with most of this deferral attributable to birds not attaining adequate 'condition' in the non-breeding season. Black-browed albatrosses followed an annual breeding pattern and most deferral of breeding in this species (approximately 6% successful birds) was also likely to be related to the attainment of breeding condition in the lion-breeding period. The mean shift lengths of the four species during incubation were significantly different and reflected the primary foraging strategy of each species. Black-browed albatrosses had the shortest shift length (3.1 ± 0.27 (s.e) days), followed by Grey-headed albatrosses (5.0 ± 0.19 days), Wandering albatrosses (8.8 ± 0.44 days) and Light-mantled sooty albatrosses (10.5 ± 0.4 days). Shift length during this time period was variable, particularly for Black-browed albatrosses, indicating that breeders were foraging different distances away from Macquarie Island, or that some were foraging more efficiently than others. Wandering albatrosses and Light-mantled sooty albatrosses had the most similar mean shift lengths during incubation and it is likely that these two species forage mostly in distant pelagic waters during this period. Shift lengths of the four species during the brood-guard period were significantly shorter and less variable suggesting that all species utilise resources close to Macquarie Island during this stage of the breeding cycle. The foraging distributions of five Grey-headed and three Black-browed albatrosses were examined during incubation and the brood-guard stage via satellite telemetry. Most foraging trips of Black-browed albatrosses were within 100 km of Macquarie Island and concentrated over the ridge system to the north and south of the island. However, one breeding bird travelled over 1 OOO km to the south to forage suggesting that this species does utilise oceanic resources distant from the breeding colony. Grey-headed albatrosses foraged primarily in oceanic waters in the Polar Frontal Zone. Most foraging activity of this species occurred 1000-1500 km east south-east of Macquarie Island, south-east of the Campbell Plateau and was usually concentrated around the edges of Sea-Surface Height Anomalies. The provisioning strategies of Light-mantled sooty albatross were also examined. Provisioning regimes were investigated at two locations over two breeding seasons. There were no significant differences between years with adults generally undertaking a long foraging trip (5-11 days) followed by 3-4 daily feeding trips. As a result the chicks were fed on average every 1.4 days to 1.6 day. Chicks fasted for up to 10 days at a time if the foraging trips of both parents were synchronised and chicks were often fed 2-3 times in one day when both parents were foraging close to Macquarie Island. The total amount of feed each chick received during its unattended life on the nest averaged 37.5 kg and the mean meal size was 518 grams and ranged from 160 g to 1.05 kg feeds in a single feed. This study has significantly increased our understanding of the conservation status and biology of these breeding populations on Macquarie Island. Factors that are likely to contribute to population changes in the future have been identified and differences between these breeding populations and populations at other subantarctic locations were documented. In general, the Macquarie Island albatross populations appeared more similar to Indian Ocean populations (e.g. Iles Crozet, Kerguelen and Marion Island) and New Zealand than those in the Atlantic Ocean (eg South Georgia). The monitoring carried out as part of this study is integral in focusing effort, both national and international, on the formulation of effective cons...