CCAMLR

Antarctic krill, Euphausia superba Dana, has a heterogeneous circumpolar distribution in the Southern Ocean. Krill have a close association with sea ice which provides access to a critical food source and shelter, particularly in the early life stages. Advective modelling of transport pathways of krill have until now been on regional scales and have not taken explicit account of sea ice. Here we present Lagrangian modelling studies at the circumpolar scale that include interaction with sea ice. The advection scheme uses ocean velocity output from the Ocean Circulation and Climate Advanced Modelling (OCCAM) project model together with satellite-derived sea ice motion vectors to examine the potential roles of the ocean and sea ice in maintaining the observed circumpolar krill distribution. We show that the Antarctic Coastal Current is likely to be important in generating the large-scale distribution and that sea ice motion can substantially modify the ocean transport pathways, enhancing retention or dispersal depending upon location. Within the major krill region of the Scotia Sea, the effect of temporal variability in both the ocean and sea ice velocity fields is examined. Variability in sea ice motion increases variability of influx to South Georgia, at times concentrating the influx into pulses of arrival. This variability has implications for the ecosystem around the island. The inclusion of sea ice motion leads to the identification of source regions for the South Georgia krill populations additional to those identified when only ocean motion is considered. This study indicates that the circumpolar oceanic circulation and interaction with sea ice is important in determining the large-scale distribution of krill and its associated variability.

Management of human impacts in the Antarctic requires an effective system of monitoring to provide information about the process being managed and the effectiveness of management actions. Human impacts arise as a result of processes that originate in the region (endogenous) and those that originate outside the region (exogenous). A number of monitoring programmes have been established in both terrestrial and marine systems to measure impacts that arise as a result of endogenous process such as fishing, tourism and research. However, most of this monitoring is surveillance monitoring, which is not linked to a specific management objective, and does not produce quantitative metrics that can be assessed and compared to agreed targets. However, defining such target levels for the Antarctic, where the aim is to minimise human impacts, is a complex process. Although potential analogues for target setting exist in other parts of the world these are generally insufficiently precautionary to be applied in the Antarctic. The challenge for scientists and policymakers working in the Antarctic is to provide quantitative measures, with agreed trigger levels, and to develop appropriate monitoring schemes to manage human impacts in the future.

The Scotia Sea ecosystem is a major component of the circumpolar Southern Ocean system, where productivity and predator demand for prey are high. The eastward-flowing Antarctic Circumpolar Current (ACC) and waters from the Weddell–Scotia Confluence dominate the physics of the Scotia Sea, leading to a strong advective flow, intense eddy activity and mixing. There is also strong seasonality, manifest by the changing irradiance and sea ice cover, which leads to shorter summers in the south. Summer phytoplankton blooms, which at times can cover an area of more than 0.5 million km2, probably result from the mixing of micronutrients into surface waters through the flow of the ACC over the Scotia Arc. This production is consumed by a range of species including Antarctic krill, which are the major prey item of large seabird and marine mammal populations. The flow of the ACC is steered north by the Scotia Arc, pushing polar water to lower latitudes, carrying with it krill during spring and summer, which subsidize food webs around South Georgia and the northern Scotia Arc. There is also marked interannual variability in winter sea ice distribution and sea surface temperatures that is linked to southern hemisphere-scale climate processes such as the El Niño– Southern Oscillation. This variation affects regional primary and secondary production and influences biogeochemical cycles. It also affects krill population dynamics and dispersal, which in turn impacts higher trophic level predator foraging, breeding performance and population dynamics. The ecosystem has also been highly perturbed as a result of harvesting over the last two centuries and significant ecological changes have also occurred in response to rapid regional warming during the second half of the twentieth century. This combination of historical perturbation and rapid regional change highlights that the Scotia Sea ecosystem is likely to show significant change over the next two to three decades, which may result in major ecological shifts.

This paper is a published book chapter examining how goals and reference points might be set for higher trophic levels – such as marine mammals, birds and fish. It briefly explores the general characteristics of objectives for higher trophic levels within the context of ecosystem-based management, noting that the emphasis for managing the effects of human activities on higher trophic levels is biased towards fisheries-based approaches rather than approaches that take into account the maintenance of ecosystem structure and function. Following this, the precautionary approach developed in the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) for taking account of higher trophic levels in setting catch limits for target prey species is described. The last section considers indicators of the status of predators with respect to establishing target and limit/threshold reference points that can be used directly for making decisions. These indicators include univariate indices summarising many multivariate parameters from predators, known as composite standardized indices, as well as an index of predator productivity directly related to lower trophic species affected by human activities.

The size-differentiated sex ratio (proportion of males: POM) of Antarctic krill was examined with an extensive dataset derived from scientific surveys in the Indian Ocean sector and the southwest Atlantic sector, and from the krill fishery in the Southern Ocean. The percentage of males in size classes of adult krill was generally high in krill of 30-35 mm total length, always low in 38-42 mm krill, sometimes showed higher values in 45-50 mm krill, but always decreased in the largest krill (>50 mm). This pattern was reproduced by a model simulation that assumed faster growth and a shorter life span for males when compared to females. These results suggest that the numbers of males should decline with time unless new recruits enter the population. Indeed, inter-annual variations in the proportion of males from the field (net collected data and penguin diet data) showed a decline in proportion of males when several years of low recruitment followed a recruitment pulse. These results lead us to conclude that male krill grow faster and have a shorter lifespan than females in the natural environment.

Antarctic krill has been studied for many decades, but we are still long way from understanding their biology to be able to make reliable predictions about the reaction of their populations to environmental change. This is partly due to certain difficulties in relation to logistics, operations and survey design associated with scientific surveys that have been obstacles for us to better understand krill biology. The krill fishery is the largest fishery in the Southern Ocean, continuously operating since early 1970s. Recent studies revealed its potential to be used as a unique source for scientific discussions to understand krill biology. In this paper, after a brief overview of krill fishery operation and krill biology, we examine how current data collection through the fishery operation could contribute to a greater understanding of krill biology, and then suggest future priorities for fisheries-related research in relation to recent changes in the Southern Ocean environment.

Reported herein are observations of Weddell seals (Leptonychotes weddellii) feeding on Antarctic toothfish (Dissostichus mawsoni) in McMurdo Sound, Antarctica, during 2001-2003 austral summers. In addition to past reports of isolated toothfish captures, the frequency of these observations and the quantity of toothfish captured lead us to suggest that this species is a significant prey item for Weddell seals, and that the recent development of a toothfish fishery in the Ross Sea may have broader impacts than expected. This is especially important in the McMurdo Sound region as toothfish are probably common (as evidenced by more than 30 years of sustained research projects on that toothfish population).