CCAMLR

Numbers of gentoo penguins Pygoscelis papua, macaroni penguins Eudyptes chrysolophus, eastern rockhopper penguins E. chrysocome filholi and Crozet shags Phalacrocorax [atriceps] melanogenis continued to decrease at Marion Island in 2003/04. The decreases are thought to be due to a reduced availability of prey to birds foraging near island. Numbers of wandering albatrosses Diomedea exulans, grey-headed albatrosses Thalassarche chrysostoma, light-mantled sooty albatrosses Phoebetria palpebrata, northern giant petrels Macronectes halli, Antarctic terns Sterna vittata and Kerguelen terns S. virgata appear stable at the island, but often with large fluctuations in numbers breeding. Numbers of dark-mantled sooty albatrosses P. fusca, southern giant petrels M. giganteus and kelp gulls Larus dominicanus have shown a long-term decrease, although the count for dark-mantled sooty albatrosses was higher in 2003/04 than for several seasons.

In South Africa, four seabirds that feed mainly on sardine Sardinops sagax and anchovy Engraulis encrasicolus all have an unfavourable conservation status or a small population: African penguin Spheniscus demersus, Cape gannet Morus capensis, Cape cormorant Phalacrocorax capensis and swift tern Sterna bergii. Availability of prey is thought to influence the populations of these species, but their food requirements have not been accounted for in management of the purse-seine fishery on sardine and anchovy. Means of identifying and attaining target populations of predators that are dependent on forage fish prey are discussed. It is suggested that criteria used by The World Conservation Union to assess the conservation status of a species may prove useful in determining minimum viable populations, and that the use of functional relationships in coupled models of predators and their prey may enable quantification of levels of escapement of prey that are necessary to maintain or rebuild populations of predators.

Three basic length groupings of krill were identified with the clustering analysis on the basis of the data of two complex surveys carried out in the western Atlantic sector of Antarctic in summer 1984 and 1988. The large-length grouping is biotopically associated with the waters of the southern branch of the Antarctic Circumpolar Current (ACC). The middle-length grouping and the small-length grouping are associated with the Weddell Sea waters. Besides, the additional fourth grouping with bimodal length structure was revealed in the survey 1988. It is assumed that the first grouping is transported into the area from the Pacific sector, while the second and the third groupings are of local origin and the forth one is formed as a result of mixing of the groupings inhabiting different biotopes under the impact of the secondary frontal zone dynamic conditions. Hydrometeorological conditions in summer 1988 complied with the climatic norm and seemed to stipulate the typical pattern of krill spatial distribution. The different distribution pattern observed during the survey 1984 was related to intensification of ACC and reduction of the Weddell waters intrusion into the eastern Scotia Sea. The comparative analysis of the survey results in 1984, 1988 and CCMLR-2000 showed that krill population structure in the western Atlantic sector of Antarctic has not actually changed.

The Convention for the Conservation of Antarctic Marine Living Resources (CCAMLR) is currently considering plausible models of the Southern Ocean ecosystem within the Working Group on Ecosystem Monitoring and Management (WG-EMM). While recognised to be an important component of this ecosystem, particularly with regard to food-web structure and function, squid have rarely been included in previous ecosystem models except perhaps to assess their potential impact as predators of Antarctic krill. This paper describes properties for three groups of squid that may be included in future ecosystem models of the Southern Ocean: onychoteuthids, ommastrephids and small – medium nektonic squids. Important ecological differences are considered to exist among these three groups (e.g. spatial and depth distribution, ontogenetic and vertical migrations). Furthermore, this paper reiterates findings from previous studies that squid should no longer be modelled as specialist predators on Antarctic krill.

This paper reports on the intersessional activities of the Steering Committee of the “Workshop on plausible ecosystem models for testing approaches to krill management” in preparation for the workshop at WG-EMM 2004. The overarching Terms of Reference are (i) to review the approaches used to model marine ecosystems, (ii) to consider plausible operating models for the Antarctic marine ecosystem, and to advance a program of work to develop and implement operating models to investigate the robustness of different management approaches to underlying uncertainties in the ecological, fishery, monitoring and assessment systems. As agreed at WG-EMM in 2003, intersessional activities have included (i) provision of advice on the potential contributions from experts in preparation for the workshop and in participating in the development of models at the workshop, (ii) a review of relevant literature and information on the development of ecosystem models elsewhere as per the first term of reference, (iii) compilation of a catalogue of available software and other simulation environments for ecosystem modelling, (iv) preliminary consideration of the requirements for datasets, estimates of parameters and other aspects related to the second term of reference, and (v) preliminary outline of the aims and specifications for ecosystem modelling as it relates to the development of management procedures for krill. The results of this work are outlined. Also provided in this report is a draft agenda for the workshop.

CCAMLR requires an assessment method for recommending a subdivision of the krill catch limit in Area 48 that will be highly likely to achieve the objectives of the convention despite the uncertainties in knowledge. This will be part of the management procedure governing the krill fishery. The agreed workplan for developing a management procedure includes the evaluation of candidate management procedures in a simulation framework, using plausible models of the Antarctic marine ecosystem. This paper develops a framework for erecting such models. It is divided into three main parts, addressing different aspects of model development. Part 1 outlines the issues to consider in assessing the requirements of plausible models. Part 2 discusses the general model requirements while Part 3 presents a possible framework for developing ecosystem models to evaluate krill management procedures. The first section of this part outlines a conceptual approach to the taxonomic/biological elements of a model and the manner in which linkages between those elements might be considered. The second section details a model framework for characterising (i) the different taxa depending on the status of knowledge and their importance for understanding the ecosystem effects of fishing, (ii) important physical processes that will influence the system and (iii) the fisheries. In developing these parts, the paper highlights areas that may be necessary to be considered by WG-EMM in the development of plausible models.

Standardized krill net sampling surveys were conducted in the Lazarev Sea (Subarea 48.6) in April 2004 and in the Elephant Island area (Subarea 48.1) in January and February/March 2004. Krill densities in the Elephant Island area were below the long-term average which mark a substantial decline after the good krill years in 2001 and 2002. Krill density was lower in the Lazarev Sea, even after taking substantial day/night differences in the catches into account. Recruitment indices of one-year- old (R1) and two-year-old krill (R2) were calculated for both areas, showing low values for R1 and high, but different values for R2. Spatial distribution of krill density and size/age classes is discussed for the Lazarev Sea. Information are given on the development of maturity stages and “re-juvenation processes” after the spawning season. Distribution and density of krill calyptopis and furcilia larvae are provided for the Lazarev Sea.

During the 1995/96 and 1996/97 summer seasons the foraging pattern of the Antarctic Shag Phalacrocorax bransfieldensis was studied by direct observation on individuals breeding at Harmony Point, Nelson Island, South Shetland Islands. During pre-laying and incubation individuals of both sexes usually foraged once a day; females early in the morning and males when their partners returned to the nests. During the rearing period the parents incremented the number of daily foraging trips usually alternating the time at sea. Compared to the incubating period, when rearing chicks individuals of both sexes reduce the extension of the foraging trips which in years of scarce food availability may no result in reducing the daily total time spent foraging due to the marked increment in the number of trips required to cover the demands at the nest. Rearing individuals respond to increasing energy requirements at the nest (i.e. as chick grew older or at increasing number of chicks at the nests) by incrementing the number of daily foraging trips and the time spent foraging. The information obtained suggest that the Antarctic Shag display mechanisms tending to buffer variable food abundance or energy requirements at the nest. The possibility of using the foraging parameters considered in this study in monitoring programmes is discussed.

The rationale for the proposed main review of the Scientific Observer Manual and a plan of intersessional work on the subject during 2004 are presented.

The Ross Sea Shelf Ecosystem (RSShelfE) offers the last chance to understand ecological processes in a system where both top-down and bottom-up forcing are still intact. Elsewhere in Earth’s oceans the systems used for understanding ecological processes and fishery effects all have lacked significant, natural top-down forcing for such a long time that it is a concept rarely considered by researchers who currently investigate open-ocean systems. Herein, the importance of top-down forcing in pelagic and neritic marine ecosystems is reviewed with concrete evidence given for its existence in the current functioning of the RSShelfE. In spite of this unique evidence for the Antarctic region, much remains to be learned about cross-component interactions in the Ross Sea system. Should the RSShelfE be un-naturally altered, an easy accomplishment given increasing fishery pressure, we will have lost the last opportunity to understand the processes that take place in a healthy, complete marine ecosystem.