John P. Croxall

Reproductive performance of female Antarctic fur seals: the influence of age, breeding experience, environmental variation and individual quality

1. The reproductive performance of female Antarctic fur seals was examined in relation to age, reproductive experience and environmental variation over 10 consecutive years (1983-92) at Bird Island, South Georgia. 2. The age at which females first gave birth varied from 3 to 6 years; over 90% of these females were 3 or 4 years of age. We found no evidence to suggest that age at primiparity had significant effects on subsequent reproduction; however, 3-year-old primiparae were less likely to be seen in subsequent years than 4-year-old primparae which may indicate a cost, in terms of survival, for females that first give birth at an early age. 3. Age-specific reproductive rates increased rapidly from ages 2 to 6 years, reached a peak of 0.80 at 7-9 years, remained above 0.75 until 11 years and then began to decline with increasing age. 4. The mean duration of foraging trips in the current year (which was used as a measure of the availability of food resources) consistently improved models of the likelihood of pupping and of weaning success. When these trips were long (indicating reduced local food resources), females returned to the breeding beaches later, fewer females pupped, they gave birth to lighter pups and weaning success was reduced. 5. The reproductive performance of older, experienced Antarctic fur seals was greater than that of younger, inexperienced animals because they had higher natality rates, gave birth to heavier pups earlier in the season, had greater weaning success and were more likely to pup the next season.

Fur seal diving behaviour in relation to vertical distribution of krill

(1) Quantitative studies of predator-prey interactions depend on a knowledge of their spatial dynamics and behaviour. Studies on marine vertebrates have hitherto been precluded by the difficulty of acquiring the relevant data. (2) Continuous records of diving depths of female Antarctic fur seals on 3-8 day feeding trips to sea from South Georgia were analysed in conjunction with data on diel changes in the abundance and distribution of their main prey, krill. (3) In 36 complete days foraging by seven seals, 75% of 4273 dives were at night. Dives then were consistently shallower (dive depth < 30 m) than in daytime (mostly 40-75 m). (4) This closely matched changes in the vertical distribution of krill, nearly all of which was below a depth of 50 m from 09.00-15.00 h, with substantial quantities above 40 m only between 21.00-06.00 h. (5) Although over 40% of krill in the water column at any time of day was below 75 m, only 3% of dives exceeded this depth. We suggest that because krill migrate vertically fur seals are able to exploit them most efficiently during shallow dives at night.

Population demography of Antarctic fur seals : the costs of reproduction and implications for life-histories

1. This study examined the costs of reproduction in terms of future survival and reproduction in female Antarctic fur seals from Bird Island, South Georgia. It used mark-recapture data from 11 consecutive years, including 3 years when several indices showed that food availability was well below average. 2. Population age structures were used, in conjunction with the measured age-specific survival rates, to estimate the rate of increase of the population as 10.7% per annum. 3. The average annual survival rate was 0.83 (SD = 0.10) with a range from 0.65 to 0.93. Survival rate showed no trend through time but was weakly correlated with pup growth rate, suggesting that it may be influenced by availability of food. Survival rate was unrelated to any other environmental or demographic parameter including population size. 4. There was no evidence of senescence. Survival rate was not related to year of birth or age, after accounting for variation due to pregnancy and calendar year. Survival was reduced as a result of pregnancy which accounted for 40-50% of adult female mortality. This effect was greatest in the age classes with the highest reproductive output (ages 5-8 years). 5. Mean pregnancy rate was 0.70 (SD = 0.11) with an interannual range of 0.59-0.88. Although females normally produced their first pups at age 3-4 years, pregnancy rate peaked at age 8 years and declined thereafter. Otherwise pregnancy rate was unrelated to the environmental or demographic variables we tested. Food availability during the pup-rearing period had no effect on pregnancy rate. 40-50% of failures to become pregnant related to animals having been pregnant in the previous year. 6. Reproduction incurs costs to females, in terms of reduced survival and future fecundity, and consequently, on average, females which survive longest tend to do so because they have lower fecundity.

Management of Southern Ocean fisheries: global forces and future sustainability

The marine resources of the Antarctic region are of global significance. In managing Southern Ocean marine resources, especially fisheries, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has adopted principles that aim: to balance harvesting and conservation; to protect the needs of dependent species, and to avoid changes that are irreversible in 20–30 years. CCAMLR has pioneered ecosystem approaches to fishery and environmental management, through the incorporation of precaution and uncertainty into its management procedures and by establishing an ecosystem monitoring programme using indicator species and processes. This pioneering application of precautionary and ecosystem approaches in the management of harvesting has met with some success, notably in applying conservative yield models for toothfish and krill stocks and in establishing strict rules for undertaking new and exploratory fisheries. However, toothfish management has been recently compromised by Illegal, Unreported and Unregulated (IUU) fishing which is driven by forces outside the Southern Ocean. Southern Ocean harvestable resources are also subject to other global forces such as environmental changes, and their management systems remain very vulnerable to rapid shifts in worldwide fishery economics, and to inadequate management in adjacent areas, particularly high seas. CCAMLR needs quickly to develop the basis of more flexible and effective management to cater for rapid shifts in capacity and demand. The complementary task, however, is to raise the management standard of other Regional Fisheries Management Organisations (RFMOs) to those of CCAMLR if global high seas marine resources are to be sustainable for the rest of this century.

Foraging white-chinned petrels Procellaria aequinoctialis at risk: from the tropics to Antarctica

In the Southern Ocean white-chinned petrels Procellaria aequinoctialis form the majority of the bird bycatch in longline fisheries. Satellite tracking of breeding birds from the Crozet islands and from South Georgia indicates that during incubation they have the longest mean foraging ranges ever recorded for a seabird, 2390 and 2190 km. Crozet birds travel to the coast of South Africa at 3495 km, into subtropical waters as well as to Antarctic waters. South Georgia birds reach the northern Patagonian shelf. In all these areas birds are potentially in contact with fisheries. These results indicate that conservation measures limited to Antarctic waters are insufficient to protect seabirds with such extensive foraging ranges.

Data on the adult marine and migratory phases in the life cycle of the southern hemisphere lamprey, Geotria australis Gray

SynopsisLarge numbers of the Southern Hemisphere lamprey, Geotria australis, have been found in the regurgitated food of albatrosses breeding on South Georgia. This finding suggests that this lamprey is found in large groups at sea, presumably associated with its host, and can travel very large distances from its natal streams. The length and morphology of the individuals from South Georgia, which almost certainly represent a South American stock, were compared with those of representatives of the immediately pre- and post-marine trophic stages of G. australis caught in Western Australia. No significant differences could be detected either in the number of trunk myomeres or in the number and arrangement of the teeth. The mean length of the animals (± 95% confidence limits) from South Georgia was 45.9 ± 0.90 cm compared with 10.0 ± 0.23 cm and 62.5 ± 0.85 cm in G. australis collected from Western Australia just before they had entered and returned from the sea respectively.

Status of white-chinned petrels Procellaria aequinoctialis Linnaeus 1758, at Bird Island, South Georgia

The white-chinned petrel (Procellaria aequinoctialis) is an abundant, widespread petrel breeding in tussock grassland at sub-Antarctic islands. Over the last decade it has been killed in large numbers in temperate and sub-tropical longline fisheries. However no data are available on the global population status. We assessed the status of white-chinned petrels at Bird Island, South Georgia by comparing the distribution and density of occupied burrows in 1981 and 1998. In both surveys white-chinned petrel burrows occurred in one-quarter of the 460–477 36-m2 quadrats surveyed. The total number of burrows in each quadrat was consistent between each survey but we estimate an overall decrease of 28% in those occupied (with considerable variation between sites). Concurrent data on breeding frequency and success showed that white-chinned petrels are essentially annual breeders at Bird Island; breeding success was consistent at around 44%. Significant factors determining densities of occupied burrows were crown height and percent tussock cover (accounting for 77% of variance). The former has decreased significantly, the latter increased significantly between 1981 and 1998 but there was no relationship between white-chinned petrel occupancy rate and habitat modification due to the presence of fur seals (Arctocephalus gazella). This suggests that any population decline is due to factors operating away from the breeding colony, such as those attributed to fishing.

The diet of white-chinned petrels Procellaria aequinoctialis , Linnaeus 1758, in years of contrasting prey availability at South Georgia

The diet of breeding white-chinned petrels was studied during the summers of 1996 and 1998 at South Georgia. Krill abundance/availability was high throughout 1996 but apparently low at the beginning of the 1998 breeding season. The diet of white-chinned petrels was similar between years and consistent with previous studies. Krill Euphausia superba (4142% by weight) was the single most important prey item followed by fish (39-29%) and squid (19-25%). Meal mass was consistent (1 10 g in 1996, 119 g in 1998) between years but a significant decrease (46%) in feeding frequency in 1998 (0.54 meals day- compared to 0.75 meals day- in 1996) resulted in 19% less food delivered to chicks in 1998 than in 1996. Breeding success, however, was consistent between years at 44% and similar to that recorded previously at Bird Island. This is in contrast to black-browed and grey-headed albatrosses, both of which experienced almost total breeding failure in 1998. It is suggested that their varied and versatile feeding methods, together with their greater diving ability, capacity to feed at night and extensive foraging range, help white-chinned petrels minimise the effects of krill shortage.

Paradigm misplaced? Antarctic marine ecosystems are affected by climate change as well as biological processes and harvesting

Abstract A recent review by Ainley et al. has suggested that recent investigations of the ecological structure and processes of the Southern Ocean have “almost exclusively taken a bottom-up, forcing-by-physical-processes approach relating individual species population trends to climate change”. We examine this suggestion and conclude that, in fact, there has been considerable research effort into ecosystem interactions over the last 25 years, particularly through research associated with management of the living resources of the Southern Ocean. Future Southern Ocean research will make progress only when integrated studies are planned around well structured hypotheses that incorporate both the physical and biological drivers of ecosystem processes.

PROVISIONING RATE AND ATTENDANCE PATTERNS OF WANDERING ALBATROSSES AT BIRD ISLAND, SOUTH GEORGIA

Abstract We investigated foraging behavior of Wandering Albatrosses (Diomedea exulans) breeding at South Georgia to assess how sex and season-specific foraging patterns relate to provisioning performance. We estimated Wandering Albatross chicks require 60–65 kg of food over the chick-rearing period; males deliver 54% of this total. Meal size delivered by both sexes remained essentially constant throughout the post-brooding chick-rearing period, but foraging trip duration varied considerably. Females made consistently longer foraging trips and delivered smaller meals but transported an average load that was 20% heavier in proportion to their body mass than males. We suggest that chick-rearing places greater demands on females compared with males and Wandering Albatrosses work hard to deliver food during the first half of chick rearing (at the expense of their own condition), thereafter reduce their work rate, presumably so as not to compromise their survival.