CCAMLR

To assess large whale stocks following the cessation of land-based South Georgia whaling in 1965, we report three independent sighting databases: a cruise in 1997, observations from Bird Island (NW of South Georgia) between 1979 and 1998, and mariner sightings between 1992 and 1997. All species were rare, with southern right whale sightings being the most common event. Two right whales photographed off South Georgia matched animals known from Peninsula Valdes, Argentina, a population known to be growing at 7% per annum. In contrast, blue and fin whales appear to be less abundant. A single blue whale mother-calf pair was observed off the Shag Rocks in February 1997. Extirpation of animals from this particular feeding ground is the most likely reason for ongoing low numbers of all species. Other factors may include: competition for krill by traditional predators such as penguins and seals and more recently by humans, an unusually high rate of natural mortality, habitat change such as alteration in sea ice coverage, and/or the impact of ongoing whaling. The history of this critical area of large-whale habitat and this report demonstrate the need for improved, consistent long-term monitoring of population trends for these depleted stocks.

There is a high degree of spatial and temporal variability in the population of Antarctic krill Euphausia superba across the Scotia Sea. Resolution of the spatial component of this variability requires a 'snapshot' of the krill population over the region (eg the CCAMLR B0 survey) whereas temporal changes have been addressed using time-series of samples from the diet of predators. At South Georgia krill in the diet of Antarctic fur seal Arctocephalus gazella show a good level of concordance with scientific net samples. In order to examine the potential of using krill in the diet of predators to examine both the temporal and spatial variability across the Scotia Sea it is essential to determine the level of concordance at other sites. Samples of krill from South Georgia, the South Orkney Islands and the South Shetland Islands, where predator foraging ranges overlap with intensive krill sampling areas within the CCAMLR B0 survey, will he collected from Antarctic fur sea scats between December and March using a standard methodology. This data will he used to example the level of concordance between krill in the diet or predators and from net hauls, to compare the timing of temporal changes in krill population between sites and to create a basis upon which to assess how the population structure during the CCAMLR B0 survey fits into a longer a longer time frame.

This study examined three competing hypotheses to explain how lactating Antarctic fur seals (Arctocephalus gazella) respond to changes in the level of resource availability. Antarctic fur seals have episodic bouts of suckling 0-3 days) , alternating with foraging trips (3-10 days). Foraging time budgets varied significantly (P

A discriminant function using simple carapace measurements corretly determined the sex of 87% of male and 89% of female Antarctic krill Euphausia superba. This facilitated the use of sex-specific regression models which increased the accuracy of total length estimates.

The distribution of whales and krill in two survey boxes north of South Georgia was examined by comparing sightings and underway acoustic data collected as part of a multidisciplinary research cruise during January/February 1998. A total of 222 cetaceans of 10 species was recorded with southern right whale (Eubalaena glacialis) and humpback whale (Megaptera novaeangliae) the two most frequent. The largest aggregation of cetaceans (21 southern right whales, 18 fin whales (Balaenoptera physalus), 4 sei whales (B. borealis), 1 humpback whale and 8 hourglass dolphins (Lagenorhynchus cruciger)) occurred close to the, largest single aggregation of krill. The level of association between baleen whales and krill was examined at a number of spatial scales. There was a positive relationship between whale abundance and mean krill density at the largest spatial scale examined (80 x 100km ). At progressively smaller scales the relationship weakened, due mainly to the increased frequency of areas of high krill density where whales were not recorded. In particular whales were absent from inshore areas (up to 300 m depth) that had higher mean krill densities compared with areas where whales were recorded. To compare krill and whale distribution, particularly at smaller scales, may require information on krill swarm structure and density. Such information may also be crucial to understanding the role of scale-dependence in potential interspecies competition among krill-feeding marine predators.

The influence of two sampling protocols on diet determination of two marine predators, the Gentoo penguin Pygoscelis papua and Antarctic fur seal Arctocephalus gazella, was investigated. The collection of diet samples on three occasions over a two week period was compared with collecting all samples during a single session, as current CEMP monitoring protocols recommend. Some differences in the mass of food recovered from penguins were found but this was attributed to the mass of penguin sampled. There were no differences in diet composition between protocols and although body mass was a significant determinant of the mean length of krill Euphausia superba recovered from penguins, there were no differences between sampling protocols. This study has shown that differences between sampling frequencies are small and a variety of sampling protocols can produce results acceptable for inter-annual monitoring. Mass of sampled individuals can account for significant variation and should be recorded, especially if sampling frequencies and sizes are low.

This study examined the feasibility of using time depth recorders (TDRs) to measure light levels experienced by a diving marine mammal. TDRs were deployed on 10 female Antarctic fur seals (Arctocephalus gazella) at Bird Island, South Georgia (54° 00' S 38° 02' W) in the 1994/5 austral summer. Depth and light measurements were made during 11 foraging trips which lasted on average (± SE) 7.1 ± 0.7 d. A total of 25657 dives were recorded with a mean dive depth and duration of 18.0 ± 3.6 m and 49.5 ± 6.9 s, respectively. Depending on time of day, fur seals experienced between 6 and 57 % of the surface illumination when diving. Illuminance ranged from full sunlight (102 lux) at the surface to minimum starlight (10-6 lux) at night and during deep daytime dives. The change in il1uminance with depth did not follow a simple exponential decrease as recorded in clear oceanic waters. TDRs recorded strong light attenuation in the top 50 m of the water column. The mean attenuation coefficient was 0.140 ± 0.014 m-1 which was in the upper range of values measured by ship surveys at South Georgia. When fur seals made shorter and shallower dives TDRs also recorded greater light attenuation. These findings suggest that Antarctic fur seals forage in relatively turbid waters containing large concentrations of phytoplankton and 1 or dense aggregations of krill. Night-time foraging and deep daytime diving indicates that fur seals are well adapted to locating prey in low illumination.

After almost a ten-year gap in fishing for Champsocephalus gunnari in the area of South Georgia and Shag Rocks, the Russian large-sized trawler ZAKHAR SOROKIN (the MOONZUND-type) attempted a short-time fishing operation in February-March, 1999. Overall, 85 pelagic trawlings yielded 264 tons of C. gunnari. Search for the fish stocks covered all the traditional sites; this allowed observers to determine a clear correlation between concentrations of adult fish and krill on the north-western shelf of South Georgia. At the same time, lasting of the feeding stocks of C. gunnari depended on weather conditions. Comparison of the obtained results with data of trawl-and-sonar surveys revealed regular occurrence of dense concentrations of C. gunnari on the north-western shelf of South Georgia.