CCAMLR

At its meeting in 2007 CCAMLR endorsed the proposal from the Scientific Committee for a joint CEP/SC-CAMLR workshop. The CEP discussed this at its meeting in June 2008 and suggested a theme of ‘Opportunities for collaboration and practical cooperation between the CEP and SC-CAMLR’. The CEP suggested that areas of common interest might include, though may not be limited to: • climate change research • ecosystem and environmental monitoring • protected areas and spatial management measures • species requiring special protection • marine pollution • biodiversity and non-native species. WG-EMM is invited to consider CCAMLR input into the Workshop agenda and work plan to inform SC-CAMLR at its meeting in October 2008.

We apply Foosa at the scale of interactions among the 3 breeding penguin colonies, krill, and environmental variability at the long-term research site in Admiralty Bay, King George Island. This work-in-progress serves 2 purposes: 1) to use historical data to estimate parameters in a model-fitting framework for the purpose of model validation, and 2) to add and explore functionality in Foosa to investigate alternative, competing hypotheses about juvenile penguin survival. Our preliminary results suggest that Foosa capably captures the general trends in adult abundance at Admiralty Bay with minimal formal estimation. Preliminary examination of top-down and bottom-up forcing on juvenile penguin survival further helps to explain trends in adult abundance. From a bottom-up perspective, there appears to be a trade-off between per-capita productivity at low adult abundance and the sensitivity of juvenile survival to foraging conditions during the first winter of life. From a top-down perspective, strong depensatory stock-recruitment dynamics suggest that understanding predatory effects on juveniles may be fundamental for understanding penguin dynamics at our study colony. To better capture the inter-annual variability in the adult abundance data, we propose future work that includes, inter alia, expanding the spatial scope to account for seasonal movement of the penguins, incorporating alternative environmental drivers, and continued hypothesis testing to make strong inference about the dominant drivers of the penguins at Admiralty Bay.

Gentoo penguins Pygoscelis papua show considerable plasticity in their diet, diving and foraging behaviors among colonies; we expected that they might exhibit similar variability over time, at a single site, since flexible foraging habits would provide a buffer against changes in prey availability. We examined inter-annual changes in the foraging strategies and diet of gentoo penguins in the South Shetland Islands, Antarctica, over five years. Antarctic krill Euphausia superba was the primary diet item, and fish the secondary, though the importance of these items varied among years. Diving behavior also varied over time; different dive depth-distributions were observed in each year. Nonetheless, chick-rearing success remained relatively constant, indicating that gentoo penguins were able to cope with differences in prey availability by altering their foraging strategy among years. We suggest that this flexibility may contribute to why gentoo penguin populations have remained stable in the region, while their congeners with less flexible foraging strategies have declined.

We provide a worked example of how a systematic conservation planning methodology (Margules & Pressey, 2000) might be used to identify important areas for conservation of biodiversity in the pelagic environment, using Subarea 48.2 (South Orkney Islands) as a pilot study area. The aim of the worked example is not to identify areas for protection or management at this stage, but rather to test the utility of this methodology, and to demonstrate the types of data and the range of decisions that would be required to undertake such an analysis. ‘MARXAN’ software (Ball & Possingham, 2000; Game & Grantham, 2008) is used to objectively determine the possible contribution of individual areas towards meeting conservation targets, using example datasets for pelagic species, bioregions and other environmental characteristics. It is concluded that this methodology could be used to provide meaningful results with those datasets currently available. With further refinement, the results from this type of analysis could be used to inform the implementation of a range of actions to conserve marine biodiversity.

The South Georgia region supports a high biomass of krill that is the subject to high inter-annual variability. The lack of a self-sustaining krill population at South Georgia means that understanding the mechanism underlying these observed population characteristics is essential to a successful ecosystem-based management of any krill fishery in the region. Krill acoustic density data from surveys conducted in the early, middle and late period of the summers of 2001 to 2005, together with krill population size structure over the same period from predator diet data, were used with a krill population dynamics model to evaluate potential mechanisms behind the observed changes in krill biomass. Krill abundance was highest during the middle of the summer in 3 years and in the late period in 2 years; in the latter there was evidence that krill recruitment was delayed by several months. A model scenario with empirically derived estimates of both the magnitude and timing of recruitment in each year showed the greatest correlation with the acoustic series. The results are consistent with a krill population with allochthonous recruitment entering a retained adult population; i.e. oceanic transport of adult krill does not appear to be the major factor determining the dynamics of the adult population. The results highlight the importance of the timing of recruitment, especially where this could introduce a mismatch between the peak of krill abundance and the peak demand from predators which may exacerbate the effects of changes in krill populations arising from climate change.

This document summarises progress by expert groups towards having manuscripts ready for the CCAMLR-IWC Workshop to review input data for Antarctic marine ecosystem models: update on progress 2008. Data collation is progressing well for all groups, except for flying birds. Draft manuscripts will be available for review at WG-EMM or from the convenors on request.

Catch uncertainty is a component of uncertainty that is not routinely considered by CCAMLR. However, given the currently reported variability in conversion factors for krill, a nominal reported catch of 600 000t could actually represent a catch in ‘green weight’ of 2.5 million tonnes. Quantifying the level of uncertainty in reported catches of krill would require information on product specific conversion factors (including the time-scale over which those conversion factors were produced) as well as the product composition of catches.

CCAMLR has agreed that there is a requirement for systematic observation from the krill fishery, however, current levels of observer coverage are not distributed evenly across years, regions or vessels. The number of observer days as a proportion of the number of days fished varied between c10% (Subareas 48.1 and 48.2) and c30% (in Subarea 48.3). 13 of the 16 vessels that have fished for krill in 48.3 have carried observers at some time, compared to 6 of 15 in 48.1 and 4 of 15 in 48.2. An analysis of existing observer data submitted to the Secretariat indicates that measuring 200 krill from 5 hauls should produce a sufficiently precise length frequency distribution and would free up time for other priority tasks of observers. Suggestions are provided for a revision of the Scientific Observer Manual for consideration by the Working Group.

The updated version of the Spatial Multi-species Operating Model (SMOM) of krill-predator-fishery dynamics described in an accompanying paper is conditioned using the WG-SAM set of reference observations for Area 48 (the SAM calendar). Results are presented for two implementations of SMOM, one with the time series of krill abundance fixed on input, and the other incorporating an explicit model of krill dynamics. Additional versions of SMOM that may need to be conditioned are discussed. In general the two SMOM implementations are broadly successful in reproducing the direction and timing of observed changes in predator abundance. The main method of conditioning involved estimating a shape parameter (the “steepness”) of the predator-prey interaction formulation. The steepness values estimated suggest that penguins respond sooner than other predators to decreasing levels of krill abundance. Given data on fish catches, the model estimates the starting (1970) fish abundance level, with results suggesting that fish populations in several of the SSMUs are much reduced compared to their 1970 levels. The conditioned operating models presented here constitute a further step towards the development of a spatially-structured Management Procedure (MP) for the krill fishery by contributing to the set of such operating models to be used to simulation test candidate MPs for robust performance. The next step involves agreeing the relative plausibilities (weights) for the different operating models. An outline of suggested future steps in the MP development process is discussed.

We present information to investigate the significance of Antarctic toothfish as a prey item for Weddell seals in the Ross Sea. • We summarise the life history of Weddell seals to provide an overview of their use of the Ross Sea. As consumption of prey by Weddell seals (both the amount and type of prey) will vary between different life history stages at different times of the year in different areas, this is relevant to the question of whether seals predate significantly on toothfish. • There is evidence that Antarctic toothfish have lower densities near to seal breeding colonies in McMurdo Sound than further away (Testa et al. 1985). • Direct information on diet of the Weddell seals, including diver observations, animal-mounted camera information, and observations from field scientists in the McMurdo Sound region suggest that toothfish are a significant prey item for Weddell seals. • In contrast, research using seal stomach contents, vomit and scats provides no evidence that Weddell seals consume toothfish at all. Diver observations suggest that seals may feed selectively on only parts of toothfish so that otoliths and vertebrae may be under-represented in remains. • Indirect information using stable isotopes of carbon and nitrogen, even including recent analyses that have not been previously reported, remains inconclusive. We recommend further research using stable isotope analysis of blood samples from seals not at the breeding colonies, and samples of muscle or other slower-turnover tissue of seals at the breeding colonies. • Information from fatty acids or other biomarkers could potentially be used to investigate the importance of toothfish as a prey item for seals, but no results are available. • We have compared mortality of Antarctic toothfish in McMurdo Sound to consumption by Weddell seals. The estimates, although preliminary and subject to uncertainty, indicate that it is possible that toothfish comprise a substantial proportion of the diet of seals in McMurdo Sound between October and January. We conclude that while there is strong evidence that toothfish are a prey item for Weddell seals in McMurdo Sound between October and January, it is plausible but unproven that they are an important prey item.