CCAMLR

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.

Conservation Measure 91/02 (2004) affords protection of the Cape Shirreff CCAMLR Ecosystem Monitoring Program (CEMP) site. Cape Shirreff is also protected as ASPA 149 through the Antarctic Treaty. The management plans for Cape Shirreff are due for review by CCAMLR in 2009 and by the ATCM in 2010. Both plans recognize the importance of the CEMP site and associated scientific research and afford area protection.

A multidisciplinary survey was conducted with the RV ‘G.O. Sars’ as part of the Antarctic Krill and Ecosystem Studies (AKES) from January to March 2008. Acoustical data were sampled continuously on six frequencies along one west-east and two south-north transects between latitudes 50 and 66.4 S in the sparsely studied CCAMLR subarea 48.6. The mean density of Antarctic krill, integrated to 270 m depth was 4.42 g/m2. The krill were mainly found in strong aggregations and were patchily distributed. The majority of the detected krill was distributed between 40 and 80 m depth, and approximately 14 % was distributed within a 100 x 100 km core area centered around the Bouvetøya.

of mean krill density in Subarea 48.4 there are premises for formation of the zones with increased density. These zones are located within the near-shore shelf-based SSMU and associated with meanders and eddy favorable for krill concentration. Here, in the cold water of the Weddell Sea, the main part of biomass of Subarea 48.4, are concentrated. In January-February, 2000, almost 60% of total biomass was concentrated here, the mean krill density was 65 g/m2, and on local grounds – greater than 150 g/m2.. Properties of the zones with increased density: these zones are associated with meanders and eddies favorable for krill concentration; observed quasistationary character of these eddies and meanders, caused by water dynamics; location of significant biomass that is formed by swarms fields, distributed in a rather narrow depth range, - obviously may promote above said zones, firstly, southern part of near-shore shelf based SSMU as an interesting to krill fishery in some seasons.

Generalized linear and additive models suggest that large proportions of inter-annual variability in the reproductive success of Adélie, gentoo, and chinstrap penguins can be explained by simple linear predictors based on local weather conditions and winter sea ice extent. Local weather variables selected by step-wise model fitting procedures corresponded to the incubation periods for each species. Sea ice extent measured during the winter prior to breeding also appears to be an important predictor of reproductive success in all species. Biological variables measured during the chick-rearing phase, like krill size, krill density at sea, and chlorophyll a concentrations appear less important, except for chinstrap penguins which breed later in the season than gentoo and Adélie penguins. In most cases, the final predictor variables detected in this analysis have exhibited directional trends, implying important effects of directional climate change on the future of reproductive success in monitored populations.

We present a quantitative food web of the Ross Sea as a step towards investigating ecosystem effects of the fishery for Antarctic toothfish (Dissostichus mawsoni). The model consolidates quantitative information on trophic links across all the major biota of the Ross Sea and tests for data consistency. The model has 38 trophic groups and is balanced in terms of annual flows of organic carbon in an average, recent year (1990–2000). The focus of the model is on the role of Antarctic toothfish in the food web, which means that the model has greater taxonomic resolution towards the top of the food web than the base. A survey of the available literature and both published and unpublished data provided an initial set of parameters describing the annual average abundance, imports, exports, energetics (growth, reproduction, consumption), and trophic linkages (diets, key predators) for each model group. We also estimated the relative level of uncertainty on these parameters. This set of parameters was not self consistent, and a method is described to adjust the initial parameter set to give a balanced model taking into account the estimates of parameter uncertainty and the large range of magnitude (>6 orders of magnitude) in trophic flows between groups. Parameters for biomass, production rate, growth efficiency, diet fractions, and other transfers of biomass between groups were adjusted simultaneously. We found that changes to the initial set of parameters needed to obtain balance were reasonably small for most groups and most parameters. The mean absolute change for all key parameters (biomass, production rate, growth efficiency) and all groups together was 1.7%, and for diet fractions was 0.6%. Large but not implausible changes in biomass, production/biomass, and production/consumption parameters were needed to balance the microzooplankton (34–47%), ice bacteria (61–72%), and ice protozoa (24–54%), components of the model. Trophic levels are in close agreement with those derived from isotopic analyses and other ecosystems. In the balanced model, there is only enough large (>100 cm) toothfish production to satisfy 6.6% of the diet of Weddell seals, 5.9% of the diet of orca, and 2.8% of the diet of sperm whales. The model does not support the hypothesis that depletion of Antarctic toothfish by fishing would change the diet of predators of toothfish (Weddell seals, orca, sperm whales) by large amounts throughout the Ross Sea, though the importance of toothfish as prey items to these predators is not tested. The model shows that large toothfish consume 61% of the annual production of medium sized demersal fishes and 14% of the annual production of small demersal fishes, implying a potential for the fishery to affect these prey through trophic cascades. There is a need to establish monitoring of medium and small demersal fishes in the Ross Sea, and to model potential changes to these groups due to the fishery.

The circulation in the Ross Sea sector of the Southern Ocean is examined in three numberical models of intermediate to high resolution. Despite the model differences (including physics, forcing) the circulation representation is relatively consistent, both in terms of the mean and some aspects of monthly variability. This could point to strong bathymetric constraints on the circulation. In particular, the models sugges a pair of cyclonic gyres separated by shallow bathymetry around 180º E that redistribute water from the wider Southern Ocean into and out of the Ross Sea. The southermost gyre boundaries comprise the Antarctic Shelf Front and the Antarctic Coastal Current. To the north the gyres are bounded by the Antarctic Circumpolar Current. The model solutions also suggest that as the model Antarctic Circumpolar Current transport reduces, the gyral transport within the Ross Sea increases. Model flows at around 900 metres compare favourably with float data. Further, model depth-averaged flow on the Ross Sea shelf is relatively consistent with that reconstructed from longline fishing records.