CCAMLR

Penguins are adapted to live in extreme environments, but they can be highly sensitive to climate change, which disrupts penguin life history strategies when it alters the weather, oceanography and critical habitats. For example, in the southwest Atlantic, the distributional range of the ice-obligate emperor and Ade´lie penguins has shifted poleward and contracted, while the ice-intolerant gentoo and chinstrap penguins have expanded their range southward. In the Southern Ocean, the El Niño-Southern Oscillation and the Southern Annular Mode are the main modes of climate variability that drive changes in the marine ecosystem, ultimately affecting penguins. The interaction between these modes is complex and changes over time, so that penguin responses to climate change are expected to vary accordingly, complicating our understanding of their future population processes. Penguins have long life spans, which slow microevolution, and which is unlikely to increase their tolerance to rapid warming. Therefore, in order that penguins may continue to exploit their transformed ecological niche and maintain their current distributional ranges, they must possess adequate phenotypic plasticity. However, past species-specific adaptations also constrain potential changes in phenology, and are unlikely to be adaptive for altered climatic conditions. Thus, the paleoecological record suggests that penguins are more likely to respond by dispersal rather than adaptation. Ecosystem changes are potentially most important at the borders of current geographic distributions, where penguins operate at the limits of their tolerance; species with low adaptability, particularly the ice-obligates, may therefore be more affected by their need to disperse in response to climate and may struggle to colonize new habitats. While future sea-ice contraction around Antarctica is likely to continue affecting the iceobligate penguins, understanding the responses of the ice-intolerant penguins also depends on changes in climate mode periodicities and interactions, which to date remain difficult to reproduce in general circulation models.

Correctly quantifying the impacts of rare apex marine predators is essential to ecosystem-based approaches to fisheries management, where harvesting must be sustainable for targeted species and their dependent predators. This requires modelling the uncertainty in such processes as predator life history, seasonal abundance and movement, size-based predation, energetic requirements, and prey vulnerability. We combined these uncertainties to evaluate the predatory impact of transient leopard seals on a community of mesopredators (seals and penguins) and their prey at South Georgia, and assess the implications for an ecosystem-based management. The mesopredators are highly dependent on Antarctic krill and icefish, which are targeted by regional fisheries. We used a state-space formulation to combine (1) a mark-recapture open-population model and individual identification data to assess seasonally variable leopard seal arrival and departure dates, numbers, and residency times; (2) a size-based bioenergetic model; and (3) a size-based prey choice model from a diet analysis. Our models indicated that prey choice and consumption reflected seasonal changes in leopard seal population size and structure, size-selective predation and prey vulnerability. A population of 104 (90–125) leopard seals, of which 64%were juveniles, consumed less than 2% of the Antarctic fur seal pup production of the area (50% of total ingested energy, IE), but ca. 12–16% of the local gentoo penguin population (20% IE). Antarctic krill (28% IE) were the only observed food of leopard seal pups and supplemented the diet of older individuals. Direct impacts on krill and fish were negligible, but the “escapement” due to leopard seal predation on fur seal pups and penguins could be significant for the mackerel icefish fishery at South Georgia. These results suggest that: (1) rare apex predators like leopard seals may control, and may depend on, populations of mesopredators dependent on prey species targeted by fisheries; and (2) predatory impacts and community control may vary throughout the predator’s geographic range, and differ across ecosystems and management areas, depending on the seasonal abundance of the prey and the predator’s dispersal movements. This understanding is important to integrate the predator needs as natural mortality of its prey in models to set prey catch limits for fisheries. Reliable estimates of the variability of these needs are essential for a precautionary interpretation in the context of an ecosystem-based management.

Goudier Island is located in the Palmer Archipelago, to the west of the Antarctic Peninsula; it is one of the most frequently visited tourist sites in Antarctica. A number of gentoo penguin (Pygoscelis papua) breeding colonies are located on the island and these have been the focus of one of the longest running experiments to examine the impacts of tourist numbers upon penguin breeding performance anywhere in the Antarctic. In this paper we describe the population trends and breeding productivity (chicks per nest) of the 10 colonies on Goudier Island, all of which have now been monitored for 12 consecutive years beginning in the 1996/1997 breeding season. Our results demonstrate that all colonies show considerable inter-annual variability for both the number of breeding pairs and breeding productivity. Of the six visited colonies, two showed an important and significant statistical decline in the number of breeding pairs. One of these declining colonies is used to determine the breeding chronology dates for all other colonies, an important part of the monitoring procedure used to assess breeding success. Our results suggest that in the future, it would be useful to control for this additional disturbance. Our results further suggest that understanding all of the many subtle influences that impact upon gentoo penguin breeding numbers is complex and that some factors may never be completely identified.

Climate change is predicted to affect marine fisheries but these effects are usually thought of as being indirect, for example through distributional changes of fish populations, changes in marine biodiversity or changes in oceanic productivity. We show that in Antarctic waters there is already evidence of direct effects of the changing physical environment – the duration of sea ice cover - on the seasonal behaviour of the region’s largest fishery, that for Antarctic krill. Declining sea ice cover in the main krill fishing grounds has resulted in greater accessibility of krill stocks to the fishing fleets, particularly during winter, and this change in fishing behaviour will need careful management in an era of rapid ecological change.

Ten years of recent finescale haul-by-haul krill data were used to characterize the behaviour of the krill fishery. Analysis of distance between hauls in relation to their catch level revealed a distinct pattern. Mean between-haul distances were generally longer when catch levels fell below 10 t per haul, and the travel distance decreased as the catch level increased; this pattern was most obvious for operations by Japanese fishing vessels. There were differences between statistical areas with longer distances moved between hauls in Area 48.1 compared to 48.2 and 48.3 reflecting the large number of fishing grounds within this area. The same patterns were observed for vessels from other nations, but were less clear. The study suggests the movement trends for Japanese vessels could form the basis for describing a generalised fishery model. Updates for some of the parameters for the krill fishery model suggested in late 1980s are proposed based on the results from this study. These analyses demonstrate the need for high quality year-round data on all vessels participating in the krill fishery to assist in interpreting the annual fishing patterns, which can best be collected by scientific observers.

Here we present three scenarios that demonstrate how cetaceans may influence the structure and dynamics of the Southern Ocean food web. These should be considered in addition to several other examples recently identified, and reviewed herein. Marine trophic cascades resulting from top-predator removal are not a novel concept. While we acknowledge the correlative nature of our examples, we nonetheless contend that they indicate fruitful directions for current and future research in the Southern Ocean. Data from the Southern Ocean are most easily attained by remote sensing, which sheds light on why, in part, researchers are preoccupied with physical factors as ecosystem drivers, i.e. climate, that lend themselves to this technology. While much of what we relate cannot be easily resolved using remote sensing, and instead requires direct observation, we hope our perspectives will enable the establishment of a broader scientific basis for management of Antarctic marine resources, which are increasingly coming under the pressure of cumulative impacts from climate change, fishing and other anthropogenic factors.

Recent analyses of anthropogenic impacts to marine systems have shown the Ross Sea to be the least affected stretch of ocean on Earth, although historical effects were not included in the study. Herein the literature is reviewed to quantify the extent of extraction of biological resources from the Ross Sea continental shelf and slope beginning at the start of the 20th century; none preceded that. An intense extraction of Weddell seals Leptonychotes weddellii by the heroic expeditions and then by New Zealand to feed sled dogs in the 1950-80s caused the McMurdo Sound population to permanently decrease; otherwise no other sealing occurred. Blue whales Balaenoptera musculus intermedia were extirpated from waters of the Shelf Break Front during the 1920s, and have not reappeared. Minke whales B. bonaerensis likely expanded into their vacated habitat, but were then hunted during the 1970-80s; their population has since recovered. Some minke whales are now taken in “scientific whaling”, twice more from the slope compared to the shelf. Other hunted cetaceans never occurred over the shelf and very few ever occurred in slope waters, and therefore their demise from whaling does not apply to the Ross Sea. No industrial fishing occurred in the Ross Sea until the 1996-97 austral summer, when a fishery for Antarctic toothfish Dissostichus mawsoni was initiated, especially along the slope. This fishery has grown since then with effects on the ecosystem recently becoming evident. There is probably no other ocean area where the details of biological exploitation can be so elucidated. It does appear that the Ross Sea continental shelf remains the least affected of any on the globe; the same can not be said of the slope.

Uncertainty exists over the importance of Antarctic toothfish (Dissostichus mawsoni) as prey of top predators in the Ross Sea. We herein assess relative weight given to direct, observational evidence of prey taken, as opposed to indirect evidence from scat and biochemical analysis, and conclude that toothfish are important to Weddell seals (Leptonychotes weddellii). The seals eat only the flesh of large toothfish and therefore they are not detected in scat or stomach samples; biochemical samples have been taken from seal sub-populations where toothfish seldom occur. Using direct observations of non-breeding seals away from breeding haulouts in McMurdo Sound, 0.8-1.3 toothfish were taken per day. Based on these and other data, the non-breeding portion of the McMurdo Sound seal population, during spring and summer, consume about 52 tonnes of toothfish. Too many unknowns exist to estimate the non-trivial amount consumed by breeders. We discuss why reduced toothfish availability to Weddell seals, for energetic reasons, can not be compensated by a switch to silverfish (Pleuragramma antarcticum) or squid. The Ross Sea toothfish fishery should be reduced including greater spatial management, with monitoring of Weddell seal populations by CCAMLR. Otherwise, likely cascades will lead to dramatic changes in the populations of toothfish dependent species.

Killer whales (Orcinus orca), both ecotype-B and -C, are important to the Ross Sea, Antarctic ecosystem; the type-C is referred to as “Ross Sea [RS] killer whale”. Herein, we review data on occurrence patterns and diet of RS killer whales, and present new information on numbers observed in the southwestern Ross Sea, 2002 - 2008. These “resident” whales appear to feed principally on fish, including the large Antarctic toothfish (Dissostichus mawsoni), as the review herein demonstrates. On the basis of sea watches from Cape Crozier, Ross Island, sighting frequency and average group size appears to have decreased; prevalence as indicated by casual observations from helicopter pilots flying over the area on a daily basis has also decreased in nearby McMurdo Sound. Consistent with a decrease in the catch-per-unit-effort of scientific fishing for toothfish in McMurdo Sound, we suggest and review evidence that the change in Ross Sea killer whale numbers in the southern Ross Sea is related to a industrial fishery-driven, density-dependent northward contraction of the toothfish stock, and not to changes in the physical (and in turn biological) environment. We surmise that in this closely-coupled foodweb, composed of very abundant penguin, seal and whale components, loss of the toothfish option for Ross Sea killer whales would force more direct competition with other predators for capture of the smaller-fish prey. Therefore, we propose, the Ross Sea killer whales have opted to move elsewhere in a scenario consistent with that of the Pacific coast of Canada, where numbers of resident killer whales have decreased following the loss of large fish as a prey choice.

This presentation addresses the need to incorporate recent studies aimed to identify different climate oceanographic regimes and its influence on krill biomass into the discussion of krill fishery management issues. Krill catch data in Subareas 48.1, 48.2 and 48.3 are compared to the AMLR Programme findings as described by Loeb et al. (2009). It is shown that krill fisheries statistics may be used to analyze the influence of the El-Niňo – Southern Oscillation (ENSO) related processes on the inter-annual variation of krill biomass distribution between the major statistical subareas. The analysis suggest that the dynamics of krill biomass in fishable aggregations in Subareas 48.1 and 48.2 is not synchronized while there are more connections between Subareas 48.1 and 48.3. Particularly strong negative anomalies of catches in the important Subarea 48.2 are seen in the year of oceanographical regime associated with La Niňa event in the South Pacific. The mechanisms for these phenomena associated with the role of the southern part of the Antarctic Circumpolar Current and the Weddell Gyre waters are discussed. In order to reach better understanding of the risks of different options for allocation of krill available catch to SSMUs the models should incorporate subarea specific krill biomass dynamics in the years with different oceanographical regime governed by ENSO.