CCAMLR

Net sampling during annual field season activities of the U.S. Antarctic Marine Living Resources (AMLR) Program yielded about average concentrations of postlarval krill during January and February-March surveys. Overall length-frequency distributions and maturity stage composition reflected good recruitment of the 1990/00, 2000/01 and 2001/02 year classes and little contribution from the 2002/03 season. Although little reproductive activity and unusually large proportions of immature individuals occurred in the Elephant Island Area during January, larval concentrations and maturity stage composition indicated a very early onset of seasonal spawning activity. Krill demographics during February-March indicated an influx of large spawning individuals; these along with greatly increased concentrations of larval stages suggested potentially good recruitment success from the 2003/04 year class.
The 2004 survey period was marked by a rapid and large-scale change in overall zooplankton abundance, composition and species abundance relations. This was similar to marked “transition periods” observed in 1994 and 1997 and, like those, was believed to result from hydrographic rather than biological processes. Qualitative differences between this and previous transition periods highlighted significant changes in zooplankton abundance and abundance relations, frequency of krill recruitment success and sea ice development that coincided with an oceanic-atmospheric “regime shift” affecting the Pacific Ocean basin.

In December 2003-January 2004 four synoptical surveys have been made in CCAMLR Division 88.1 (Ross Sea): acoustic survey on two krill species (E. superba and E. crystallorophias), net samplings on krill and other pelagic species, visual samplings on krill predators, CTD and XBT samplings on the water masses. The paper describes aim and carrying out of the project, instruments and methods used and presents some preliminary results.

This paper reports on the discussions that occurred among individuals tasked by the WG-EMM to continue review of the CEMP Standard Methods and their delivery to the CEMP database. The discussions were diverse in covering a wide range of parameters, methods and issues, but in the limited time available it was not possible to discuss all aspects of CEMP. The issues considered are presented under broad themes with some historical background to the development of those themes provided as context. Issues relating to each theme that were discussed by the group are summarised, and recommendations for any work or action are provided.

In comparison to other homeotherms, young recently weaned marine mammals in high latitudes face exceptional energetic demands when foraging and thermoregulating. Lipids are an important source of energy and a major component of insulation that allow them to meet these demands. To examine the role of lipid stores in a high-latitude pinniped, the body composition and thermoregulatory capabilities of Antarctic fur seal (Arctocephalus gazella) pups and yearlings were measured via flow-through respirometry and hydrogen isotope dilution. From these data we constructed a model to examine the importance of post-weaning fasting capability in free-ranging, young fur seals. Resting metabolic rates were different for pups and yearlings measured in 0.6 ºC water, 10.3 ºC water, and ambient air; however, mass and percent lipid as covariates accounted for the different metabolic responses in pups and yearlings for all treatments. The estimated lower critical temperature for combined pups and yearlings was 14.4 ºC, 10 to 15 ºC above water temperatures normally experienced by Antarctic fur seals. Modeling predicted that a weaned fur seal pup would survive at-sea from 9.8 to 36.2 days before succumbing to starvation. The most likely maximum travel distance within this time constraint suggests food resources close to the natal rookery are important to first year survival for this species.

The cephalopod diet of the Gentoo penguin, Pygoscelis papua and the Antarctic fur seal, Arctocephalus gazella was comparatively analyzed at Laurie Island, South Orkney Islands. A total of 125 stomach samples were collected by the water off-loading method from Gentoo penguins during the autumns of 1993, 1995 and 1996, and 39 fur seal scats were collected from mid March to April 1988. Cephalopods preyed upon by Gentoo penguins were represented by 1974 beaks (1628 lower, 346 upper) which occurred in 50.4% of the samples. Lower beaks identified belonged exclusively to the squid Psychroteuthis glacialis. The mean lower rostral length (LRL) of these beaks was 1.1 mm (range 0.4 - 1.8 mm). From the Antarctic fur seal scats 103 beaks (41 lower, 62 upper) were removed from 60.6% of scats which contained prey remains. The cephalopod species identified were Slosarczykovia circumantarctica and P. glacialis which constituted 78.8% and 21.1% in terms of numbers, respectively. The mean lower rostral length for S. circumantarctica was 2.7 mm (range 2.0 - 3.5 mm), while that of P. glacialis was 1.6 mm (range 1.0 - 2.5 mm). The foraging behaviour of the two top predators was analyzed and discussed according to the composition and size of their cephalopod prey.

An ecosystem approach for the management of human activities in the Southern Ocean is enshrined in the principles of the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). The implementation of such an approach requires an understanding of the wider dynamics of the ecosystem, which is best achieved through the development of ecosystem models. However, not all models will be suitable for developing an ecosystem approach to management. To facilitate the development of ecosystem models appropriate for CCAMLR, we review the existing models of Southern Ocean ecosystems that include krill and the higher trophic levels. We also briefly consider modelling approaches from elsewhere in the world. The main categories we consider are models of krill populations and life cycles, predator-prey models and models of ecosystems. A range of approaches has been developed in each of these categories and we review the major results of each approach. Finally, we discuss the issues highlighted by the studies that are still relevant today, and we note where major requirements for model development were identified.

Results of acoustic surveys carried out in winter months of 2000 and 2002 demonstrate significant distinctions in spatial distribution patterns of krill in the northwestern and the northeastern parts of South Georgia area. The boundary between two areas is located at about 37°30/ W. It is shown that in winter months in the northwestern part where foraging areas of dependent predators are located is non-attractive to fishery . The observed grounds with krill density exceeding the threshold value 100 g/m2 determined as potential fishing grounds were located in the northeastern part of South Georgia.
Comparison of krill aggregations structure in the northwestern and the northeastern parts of South Georgia area allows to assume that dispersed aggregation (layer and irregular forms) much more suits to the foraging tactics of dependent predators than krill distribution in the form of dense swarms or patches, which on the contrary are attractive to the fishing fleet. The considered results show that not only krill biomass density, but also its availability determined by krill aggregations distribution, will be very important both to fishery and to dependent species,

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). This paper describes properties for two groups of marine mammals that may be included in future ecosystem models of the Southern Ocean: cetaceans and pack-ice breeding seals. Important ecological differences exist among and between these groups, which should be considered in the development such models.