CCAMLR

Life-history theory predicts that adults of long-lived species such as seabirds should optimally balance investment in current and future offspring. However, when trying to optimize investment in offspring provisioning, the most energetically costly component of seabird parental care, adults need to contend with large interannual fluctuations in prey availability and hence the cost of chick provisioning. Adults faced with this uncertainty can mechanistically balance parental care by adopting a strategy somewhere along the continuum between maintaining constant investment in foraging effort between years and letting chick provisioning fluctuate or holding chick provisioning constant and varying investment in foraging effort. Using ship-based hydroacoustic assessment of prey, time-depth recorders attached to penguins and land-based observations at the breeding colony, we examined how foraging and reproductive effort in breeding chinstrap penguins Pygoscelis antarctica responded to interannual variation in the abundance of Antarctic krill Euphausia superba in the vicinity of Seal Island, South Shetland Islands, 1990–1992. Regional measures of krill density varied by a factor of 2.5 (47.0, 23.8 and 61.2 gm–2 in 1990, 1991 and 1992, respectively) and was correlated with annual measures of breeding adult body weight and reproductive performance (breeding population size, duration of chick rearing, chick growth, breeding success and fledgling weight). In contrast, measures of penguin foraging effort (dive depth, dive duration, number of trips day–1, trip duration, number of dives trip–1 and dive rate) did not differ between years. We conclude that chinstrap penguins reduce reproductive success rather than increase foraging effort in response to decreases in prey abundance in a manner consistent with predictions of life-history strategies for long-lived seabirds.

The spatial and temporal variability in the fish component of the diet of Antarctic fur seals Arctocephalus gazella (Peters 1975) in the Atlantic sector of the Southern Ocean was examined using diet data from ten sites in the region including a 13 year time-series from South Georgia. The fish species composition in the diet at each site showed a strong relationship with the local marine habitat/topography. The absence of formerly harvested fish species indicates a lack of recovery of stocks of Notothenia rossii (Richardson 1844) at South Georgia and Champsocephalus gunnari (Lönnberg 1905) at the South Orkney Islands. At South Georgia Protomyctophum choriodon (Hulley 1981), Lepidonotothen larseni (Lönnberg 1905) and C.gunnari were the most important species in the diet between 1991 and 2004. Variability in the occurrence of the C. gunnari was driven mainly by annual scale processes, particularly those that influence the availability of Antarctic krill Euphausia superba (Dana 1852). The occurrence of the pelagic P. choriodon was primarily influenced by shorter-term water mass changes within the foraging range of the seals. The fish composition in the diet reflects differences in marine habitat/topography as well as variability at a range of time-scales that reflect environmental variability and harvesting.

We used satellite telemetry methods to study macaroni penguins at South Georgia to determine how they ranged from their colonies during the early part of their breeding season at a time when they are constrained to return to their chick on a near-daily basis. The principal objectives of this study were to examine whether animals exploit major oceanographic features where prey may be more predictable; whether animals from one colony forage in separate locations to those from nearby colonies; or, whether animals range evenly over the available area. Results show that animals did not range evenly, that animals from one colony tended to forage in locations separate to those used by animals from nearby colonies (or at least overlap was restricted), and that though birds from some colonies foraged within waters influenced by major oceanographic features such as the southern Antarctic Circumpolar Current front, not all birds in the region focused on such areas as some birds foraged in other oceanographic contexts. The results from this study highlight the complexity of foraging dynamics for colonially nesting seabirds; they also help inform management models currently being developed for Antarctic krill fisheries, a potential competitor for the main prey of macaroni penguins.

Climate warming and associated sea ice reductions in Antarctica have modified habitat conditions for some species. These include the congeneric Adélie, chinstrap and gentoo penguins, which now demonstrate remarkable population responses to regional warming. However, inconsistencies in the direction of population changes between species at different study sites complicate the understanding of causal processes. Here, we show that at the South Orkney Islands where the three species breed sympatrically, the less ice adapted gentoo penguins increased significantly in numbers over the last 26 years, whereas chinstrap and Adélie penguins both declined. These trends occurred in parallel with regional long-term warming and significant reduction in sea ice extent. Periodical warm events, with teleconnections to the tropical Pacific, caused cycles in sea ice leading to reduced prey biomass, and simultaneous inter-annual population decreases in the three penguin species. With the loss of sea ice, Adélie penguins were less buffered against the environment, their numbers fluctuated greatly and their population response was strong and linear. Chinstrap penguins, considered to be better adapted to ice-free conditions, were affected by discrete events of locally increased ice cover, but showed less variable, nonlinear responses to sea ice loss. Gentoo penguins were temporarily affected by negative anomalies in regional sea ice, but persistent sea ice reductions were likely to increase their available niche, which is likely to be substantially segregated from that of their more abundant congeners. Thus, the regional consequences of global climate perturbations on the sea ice phenology affect the marine ecosystem, with repercussions for penguin food supply and competition for resources. Ultimately, variability in penguin populations with warming reflects the local balance between penguin adaptation to ice conditions and trophic-mediated changes cascading from global climate forcing.

Climate variability has strong effects on marine ecosystems, with repercussions that range in scale from those that impact individuals to those that impact the entire food web. Climate-induced changes in the abundance of species in lower trophic levels can cascade up to apex predators by depressing vital rates. However, the characteristics and predictability of predator demographic responses remain largely unexplored. We investigated the delectability, limits, and nonlinearity of changes in Antarctic fur seal pup production at South Georgia over a 20-year period in response to environmental autocorrelation created by global climate perturbations; these were identified in time series of monthly averaged sea surface temperature (SST). Environmental autocorrelation at South Georgia was evident with frequent SST anomalies between 1990 and 1999, during a decade of warm background (time-averaged) conditions. SST anomalies were preceded by, and cross-correlated with, frequent El Niño-La Niña events between 1987 and 1998, which was also a decade of warm background conditions in the tropical Pacific Ocean. Nonlinear mixed effects models indicated that positive anomalies at South Georgia explained extreme reductions in Antarctic fur seal pup production over 20 years of study. Simulated environmental time series suggested that the effect of anomalies on Antarctic fur seals was only detectable within a narrow range of positive SST, regardless of the distribution, variance, and autocorrelation structure in SST; this explained the observed nonlinearity in responses in pup production, which were observed only under persistent high SST levels. Such anomalies at South Georgia were likely associated with low availability of prey, largely krill, which affected Antarctic fur seal females over time scales longer than their breeding cycle. Reductions in Antarctic fur seal pup production could thus be predicted in advance by the detection of large-scale anomalies, which appeared to be driven by trends in global climate perturbation.

Our ninth complete consecutive season of seabird research at Cape Shirreff allowed us to assess trends in penguin population size, as well as inter-annual variation in reproductive success, diet and foraging behaviour. The gentoo penguin breeding population declined marginally from the previous season and is the third lowest population size in the 10 years of census data. The chinstrap penguin breeding population has been declining for the Past eight years and is at its lowest size in the 10 years of study. Gentoo penguin fledging Success was the highest recorded in all the years of study. The fledging success for chinstrap penguins was noticeably higher during the 2005/06 season than in the previous season and was slightly higher than the previous eight year mean. Gentoo penguin fledge weights for this season was the highest recorded in all the years of study. Chinstrap penguins fledge weights increased slightly from the 2004-05 season and were close to the previous eight year mean. Both gentoo and chinstrap penguin diets were comprised mainly of adult female Antarctic krill, the majority of which were 51-55mm in length. This is a continuation of a four year trend with increasing proportions of female krill and increasingly larger krill. Chinstrap penguin total chick meal mass was lower than almost all of the previous eight years of diet sampling; however, foraging trip durations were shorter than during the 2004/05 season. This may indicate that the provisioning rate of chicks by adults may have been higher, which would account for this difference. This interpretation may be aided by analysis of foraging location and diving behaviour data to be done at a later date.