CCAMLR

The numbers of gentoo penguins Pygoscelis papua breeding at subantarctic Marion Island fell by 40%, from 1994/95 to 2002/03 from 1 352 pairs to 806 pairs. Apart from a slight increase in 1998/99, there was a steady decrease in numbers breeding between 1995/96 and 2000/01, when the population stabilized. There is indication that in some years not all breeders nested and that some birds relocated to another colony after disturbance. From first clutches, pairs on average fledged between 0.01 chicks in 1997/98 and 0.58 chicks in 2002/03 (mean 0.38 ± 0.21). In 1994/95, replacement clutches increased the overall production of fledged chicks by 11%. Based on demographic parameters measured at other localities, the production of chicks at Marion Island was inadequate to maintain the population during the period 1995/96–2000/01. Consistency in trends in breeding success at five colonies suggests that factors operating at a mesoscale, rather than those specific to particular colonies, often influenced breeding success. Laying was later than normal in 1997/98, when there was almost total breeding failure with large losses of eggs and small chicks to returning Subantarctic skuas Catharacta antarctica. Future research on this Near Threatened species at Marion Island must take full account of its susceptibility to human disturbance.

There is indication that numbers of macaroni penguins Eudyptes chrysolophus at subantarctic Marion Island have decreased since the early 1980s. Estimates of the population at the island fell from about 405 000 pairs in 1983/84 and 434 000 pairs in 1994/95 to about 356 000 pairs in 2002/03. Two large colonies, at Bullard Beach and Kildalkey Bay, account for about 85% of the overall population. At both these colonies the area occupied by breeders showed no trend between 1983/84 and 2002/03, but the mean density of nests decreased. However, error on estimates of abundance at these colonies precludes demonstration of a significant decrease in the overall population. Numbers of occupied nests at other colonies decreased from 79 000 in 1994/95 to 31 000 in 2002/03. At three small colonies there was a significant decrease of 88% between 1979/80 and 2002/03, most of the decrease occurring after 1983/84. At Marion Island, macaroni penguins usually breed for the first time when aged about three years. From 1994/95–2002/03, pairs fledged on average 0.46 chicks per year, an amount thought insufficient to maintain the population. However, during this period there was a significant increase in reproductive success with time. In the same period, the masses of males and females on arrival at breeding colonies were significantly correlated. Both showed a marked decrease in 1998/99, after the El Niño of 1997/98. In most seasons from 1994/95–2001/02 crustaceans dominated the food, but the mass of chicks at fledging was significantly related to the contribution of fish to the diet.

South Africa’s subantarctic Prince Edward Islands support substantial proportions of the global populations of a number of surface-nesting seabirds. Populations of most of these have decreased at the islands since the 1980s and 12 of 16 species are regarded as Threatened or Near Threatened regionally or internationally. The main causes of population decreases are thought to be by-catch mortality of albatrosses and giant petrels in longline fisheries, and environmental change influencing availability of prey to penguins and the Crozet shag Phalacrocorax [atriceps] melanogenis. It is proposed that the Prince Edward Islands Special Nature Reserve be expanded to include surrounding territorial waters so as to afford additional protection for seabirds breeding there, especially those species feeding near to the islands. Consideration needs also to be given to listing species as threatened or protected in terms of planned new legislation in South Africa and then developing management plans for them, preferably linked closely with the Agreement on the Conservation of Albatrosses and Petrels and the National Plan of Action (NPOA) – Seabirds. The islands should also be nominated as a Ramsar Wetland of International Importance in recognition of their importance to seabirds, with 13 of the 16 species exceeding the 1% of the global population criterion. A combination of research, monitoring and legislation will help conserve the surface-nesting seabirds of the Prince Edward Islands into the 21st century, but only providing the effects of climate change can somehow be addressed.

In 1997/98, breeding at subantarctic Marion Island was exceptionally good for five species of seabirds capable of foraging over wide areas and for a tern. The number of king penguin Aptenodytes patagonicus chicks surviving to the start of spring in 1997 was considerably more than previously recorded. Greater numbers of wandering Diomedea exulans and grey-headed Thalassarche chrysostoma albatrosses, northern giant petrels Macronectes halli and Kerguelen terns Sterna virgata bred than previously recorded, and more southern giant petrels M. giganteus did so than in any other year since 1994. For southern giant petrels, reproductive success was higher than in any other year, as was survival of chicks of northern giant petrels. Conversely, for two seabirds that feed close to the island, gentoo penguin Pygoscelis papua and Crozet shag Phalacrocorax [atriceps] melanogenis, 1997/98 was a particularly poor breeding season. Gentoo penguins initiated breeding later than usual and fledged few chicks. The number of Crozet shags that bred decreased; probably about 25% of the adult population did not breed. For two species with an intermediate foraging range that eat mainly crustaceans, macaroni Eudyptes chrysolophus and rockhopper E. chrysocome penguins, breeding was not noticeably different from normal except that chicks of rockhopper penguins fledged with a slightly heavier mass than in other years. However, for both these penguins, the mass of adults on arrival at colonies decreased substantially in the following (1998/99) breeding season. The unusual breeding by most of the seabirds coincided with the El Niño Southern Oscillation (ENSO) event of 1997/98. This synchrony contrasts with lagged responses to ENSO events of seabirds that breed farther south in the Southern Ocean. Continued monitoring of seabirds over well-separated sites in the Southern Ocean may elucidate how climatic perturbations operating at a global scale impact seabirds in the region.

The oldest known wandering albatross Diomedea exulans at the Prince Edward Islands is estimated to have been approximately half a century old when last recaptured in 2001. Demographic studies need to continue for several more decades before the true maximum longevity of the species becomes evident.

The subantarctic Prince Edward Islands (Marion and Prince Edward) support the largest breeding population of the Vulnerable wandering albatross Diomedea exulans. The numbers of birds breeding in the Marion Island population has fluctuated over the past three decades and appears to be the result of both real changes in the size of the population and changes in the proportion of the population that attempts to breed in a given year. Changes in several demographic parameters that appear to be influenced by both environmental and anthropogenic effects are described. The proportion of first-time breeders in the population was positively correlated with the maximum ENSO index, whereas the annual survival rates of breeding adults were negatively correlated with Japanese pelagic longline fishing effort in the southern Indian Ocean. Adult survival rates were significantly correlated with those recorded on neighbouring Possession Island (Crozet Islands) but differed from those at South Georgia, suggesting common factors operating at an ocean-basin scale. The average survival rate of adult females was lower than that of males. Males who lost partners took 40% longer than females to find a new mate, suggesting a male-biased population. Survival rates of juvenile males and females did not differ. The age distribution of first-time breeders has shifted progressively towards younger birds during the 1990s. Higher than expected survival rates of breeding adults during the late 1990s may be linked to large amounts of supplementary food being made available by the initiation of a longline fishery for Patagonian toothfish Dissostichus eleginoides close to the islands during this time. Overall, breeding success was better than recorded at other localities, indicating that breeding conditions at Marion Island were comparatively favourable. The early implementation of both international and national conservation initiatives to reduce the impact of longline fishing on this species and improve its conservation status is strongly encouraged.

Numbers of rockhopper penguins Eudyptes chrysocome breeding at Marion Island decreased from about 173 000 pairs in 1994/95 to about 67 000 pairs in 2001/02. During 1994/95-2002/03 pairs fledged on average 0.40 chicks per annum, an amount thought insufficient to balance mortality of breeding adults, and there was a decrease in the mass at arrival at breeding colonies of both males and females. Except in 1997/98, the mass of chicks at fledging was less than that recorded at two other localities. These factors suggest an inadequate supply of food for rockhopper penguins at Marion Island. Decreases of rockhopper penguins at several other localities also have been attributed to inadequate food. Rockhopper penguins at Marion Island continued to feed mainly on crustaceans during chick rearing. There was a marked increase in the contribution of fish to the diet in 1999/00 that coincided with an increase in mass at arrival at colonies of both males and females. Trends in numbers of pairs breeding in different sections of Marion Island were not always consistent, indicating the need of wide-scale monitoring to establish the overall trend.

The first midsummer survey of surface-nesting seabirds at Prince Edward Island was conducted during December 2001. It was also the first census for most species since the early 1980s. Despite concerns about the impacts of longline fishing mortality on various albatrosses and giant petrels, there was no evidence that populations of these species had decreased. Indeed, the estimate of wandering albatrosses Diomedea exulans (Vulnerable) has increased significantly, making Prince Edward Island equal with Marion Island as supporting the largest single-island populations of this species. Species that underwent significant decreases were macaroni penguins Eudyptes chrysolophus (Vulnerable), Crozet shags Phalacrocorax [atriceps] melanogenis and Kerguelen terns Sterna virgata (Near-Threatened). The reasons for these decreases are unclear, but for macaroni penguins may be partly a consequence of competition for space with the burgeoning population of fur seals Arctocephalus spp. The 2001 survey increased the population estimates for Subantarctic skuas Catharacta antarctica, lightmantled sooty albatrosses Phoebetria palpebrata (Vulnerable) and southern giant petrels Macronectes giganteus (Vulnerable), mostly as a result of greater coverage than for previous counts. The 2001 survey confirms that Prince Edward Island remains a globally important breeding site for seabirds.

During the 1990s and early 2000s, populations of surface-nesting seabirds at Marion Island showed different trends, but for the majority of species numbers decreased. Reduced numbers of gentoo penguins Pygoscelis papua, eastern rockhopper penguins Eudyptes chrysocome filholi, Crozet shags Phalacrocorax [atriceps] melanogenis and probably macaroni penguins E. chrysolophus are most plausibly attributed to an altered availability of food. Decreases in numbers of dark-mantled sooty albatrosses Phoebetria fusca, light-mantled sooty albatrosses P. palpebrata, southern giant petrels Macronectes giganteus and possibly northern giant petrels M. halli may have resulted from mortality of birds in longline fisheries. However, populations of wandering Diomedea exulans and grey-headed Thalassarche chrysostoma albatrosses fluctuated around a stable level. Numbers of Subantarctic skuas Catharacta antarctica and kelp gulls Larus dominicanus breeding at Marion Island also decreased. Kerguelen Sterna virgata and Antarctic S. vittata terns remain scarce at the island. Trends for king penguins Aptenodytes patagonicus were not reliably gauged, but numbers probably remained stable or increased. There were large fluctuations in numbers of king penguin chicks surviving to the end of winter.

Mackerel icefish, Champsocephalus gunnari (Lönnberg), at South Georgia and Shag Rocks in the Southern Ocean have supported a fishery since the 1970s. This study has analysed the length-frequency distribution of C. gunnari from 10 bottom trawl surveys at South Georgia and 9 at Shag Rocks between 1987 and 2002. Most surveys were between December and February (summer), with one in September (Spring). Mean total lengths (TL) of age-classes were determined for each year by examining length frequency plots and tables, and by using CMIX. These methods were only applied where there was distinct modality in the length-frequency distributions. Lengths of age-classes derived by these two methods were not statistically different. Age-class 1 was found for all surveys at South Georgia but was absent for 3 years at Shag Rocks, potentially indicating greater recruitment variability at Shag Rocks. Age-class 4 was found for 8 surveys at South Georgia but for only 1 survey at Shag Rocks, indicating likely differences in mortality between localities. To compensate for variation in the time of surveys, the mean TL of age-classes were standardized to a common day of the year (16 January) based on the Bertalanffy growth curve. The CMIX estimated mean TL of age-classes 1, 2 and 3 were, respectively, 14.5, 23.8 and 30.2 cm at South Georgia, and 18.6, 26.8 and 33.6 cm at Shag Rocks. The mean TL of each age-class of C. gunnari at Shag Rocks was significantly larger than at South Georgia, although the annual growth increment at each locality was similar. This is further evidence that C. gunnari probably hatch earlier at Shag Rocks. A difference in hatching period between the two localities and differences in recruitment and mortality indicates that the mackerel icefish populations at South Georgia and Shag Rocks should be managed as two different stocks. At South Georgia, the mean TL of age-class 1 decreased significantly between 1987 and 1994, and this change was negatively correlated with summer sea surface temperatures during the previous year. Summer maximum sea surface temperatures at South Georgia have increased significantly between 1950 and 2000, and this shift in temperatures is likely to have changed the seasonal timing and level of primary production. The decreased size of C. gunnari may be the result of reduced nearshore food availability linked to climate variability.