Changing circumpolar distributions and isoscapes of Antarctic krill: Indo‐Pacific habitat refuges counter long‐term degradation of the Atlantic sector

The Southern Ocean provides strong contrasts in rates and directions of change in temperature and sea ice between its sectors, but it is unknown how these affect plankton species that are distributed right around Antarctica. Here, we quantify the changing circumpolar distributions of Antarctic krill, based on the CHINARE 2013/14 circum-Antarctic expedition, plus independent analyses of compiled abundance data (KRILLBASE:1926–2016). In the 1920s–1930s, average krill densities in the Atlantic-Bellingshausen sector were eight times those in the other sectors. More recently, however, the concentration factor has dropped to only about twofold. This reflects a rebalancing broadly commensurate with climatic forcing: krill densities declined in the Atlantic Bellingshausen sector which has warmed and lost sea ice, densities may have increased in the Ross-Pacific sector which showed the opposite climatic trend, while densities showed no significant changes in the more stable Lazarev-Indian sectors. Such changes would impact circumpolar food webs, so to better define these we examined circumpolar trends of isotopic values in krill and other zooplankton based on the CHINARE cruise and a literature meta-analysis. Krill δ15N values ranged significantly between sectors from 2.21‰ (Indian) to 3.59‰ (Ross-Pacific), about half a trophic level lower than another key euphausiid, Thysanoessa macrura. These isoscapes form a baseline for interpreting the reliance of predators on euphausiids, within the varying food webs around the continent. Overall, we suggest that the Indo-Pacific sector has acted as a refuge for the circumpolar krill stock while conditions for them deteriorated rapidly in the Atlantic sector

Using habitat models for chinstrap penguins Pygoscelis antarctica to advise krill fisheries management during the penguin breeding season

Aim: To predict the at‐sea distribution of chinstrap penguins across the South Orkney Islands and to quantify the overlap with the Southern Ocean krill fishery. Location: South Orkney Islands, Antarctica. Methods: Penguins from four colonies across the South Orkney Islands were tracked using global positioning systems (GPSs) and time depth recorders (TDRs). Relationships between a variety of environmental and geometric variables and the at‐sea distribution of penguins were investigated using general additive models for the three main phases of the breeding season. Subsequently, the final models were extrapolated across the South Orkney archipelago to predict the at‐sea distribution of penguins from colonies where no tracking data are available. Finally, the overlap between areas used by chinstrap penguins and the krill fishery was quantified. Results: The foraging distribution of chinstrap penguins can be predicted using two simple and static variables: the distance from the colony and the direction of travel towards the shelf‐edge, while avoiding high densities of Pygoscelis penguins from other colonies. Additionally, we find that the chinstrap penguins breeding on the South Orkney Islands use areas which overlap with frequently used krill fishing areas and that this overlap is most prominent during the brood and crèche phases of the breeding season. Main conclusions: This is the first step in understanding the potential impacts of the krill fishery, for all colonies including those where no empirical tracking data are available. However, with the available data, it is not currently possible to infer an impact of the krill fisheries on penguins. With this in mind, we recommend the implementation of monitoring schemes to investigate the effects of prey depletion on predator populations and to ensure that management continues to follow a precautionary approach and is addressed at spatial and temporal scales relevant to ecosystem operation

Prospects for a sustainable increase in the availability of long chain omega 3s: lessons from the Antarctic krill fishery.

• The global summit on nutrition, health and human behaviour (GSNHHB) identified the objective of increasing “the availability of long chain Omega‐3 (especially docosahexaenoic acid) for human consumption in a sustainable, environmentally responsible way”. • The objectives of management for sustainability include maintaining continuity of supply and limiting negative impacts. These objectives have associated challenges which are best illustrated using a case study. • Marine fisheries are likely to remain the main source of docosahexaenoic acid (DHA) for the foreseeable future. I use the example of the Antarctic krill fishery, which is a minor but high value source of DHA, to illustrate the issues, processes, actors and risks involved in attempting to manage natural resources in a sustainable, environmentally responsible way. • One of the key issues is uncertainty: The natural state of ecosystems, how they respond to exploitation, and how these responses will be affected by environmental change are not clearly understood. The solution is to use “precautionary” measures, which often means catching less than is theoretically possible, and additional restrictions on where the fishery can operate. • The “sustainability” of the Antarctic krill fishery has been questioned in a way that has impacted the delivery of Antarctic krill products to consumers. In reality, the fishery is one of only 3% of fisheries worldwide that the Food and Agriculture Organisation of the United Nations considers “under-exploited” and one of the few that have a management approach committed to limiting impacts on the both the target stock and the wider ecosystem. Disagreement arises partly because there is no universal agreement about the definitions of “sustainable” and “environmentally responsible” or about the standards of evidence required to support a claim. A potential solution is to identify the different objectives that people have for the ecosystem, and to agree acceptable trade-offs, levels of risk, and standards of evidence. This approach is compatible with the ecosystem approach to fisheries recommended by the 2002 World Summit on Sustainable Development. • The GSNHHB’s commitment to sustainability is a positive step which should be followed by engagement with suppliers to support the appropriate management and recovery of fished ecosystems. • GSNHHB’s objectives imply an increase in supply beyond the capacity of marine fisheries and therefore the development of alternative sources. • The steps towards sustainability are similar for all sources. They include identifying the different objectives that people have for the source ecosystem, evaluating the risks of not achieving these objectives, establishing trade-offs between objectives, and ensuring appropriate monitoring. It is essential for groups with an interest in source ecosystems to work with each other, and with scientists and managers, to achieve these steps