CCAMLR

One hundred and thirty nine stomach contents of the blue-eyed shag Phalacrocorax atriceps were sampled at Nelson Island, Antarctica, between 1 December 1994 and 2 February 1995. Fish were by far the main prey, followed by octopods, gammarids, euphausiids and polychaetes. Notothenia coriiceps, predominated in frequency (56%) and in mass (55%), whereas Harpagifer antarcticus was the most important by number (60%). The mean mass of the stomach contents was 220 g, whereas the mean number of fish was 7.4 (range 1-34). Eight hundred and sixty four bird h-1 of observations on 5-7 nests showed that the adults averaged 1.7 trips day-1 during incubation, 2.0 trips day-1 in early rearing and 4.6 trips day-1 during late rearing period. The estimated daily intakes reached 352, 462 and 1017 g respectively.

The analysis of twenty nine stomach contents collected in a colony close to Pirie Peninsula, South Orkney Islands, from 2 January to 18 February 1995, showed that fish were by far the main prey of the blue-eyed shag Phalacrocorax atriceps, followed by octopods, decapods and gammarids. Notothenia coriiceps constituted the bulk of the diet; however, its importance decreased by the end of the study when Nototheniops nudifrons was the most important prey. The composition of the diet varied throughout the breeding season according to changes in the chicks' energetic demands. The results are compared to those obtained previously in the area and the possibility that the stomach contents primarily represents the chicks diet is discussed.

Detection of climate-induced change in marine ecosystems requires a knowledge of the underlying variability of the environment. This paper uses a range of datasets to investigate the interannual variability in Southern Ocean sea-ice dynamics. We present the first analysis of a series of fast-ice duration data from Signy Island, which we have cross-calibrated and combined with an earlier series from the same island group. The combined series covers the period from 1903 to the present day. The analyses indicate that there has been a long term decline in the duration of sea-ice at the South Orkney Islands in the north-west Weddell Sea. This change has not been a simple linear decline but appears to have been the result of a reduction in the duration of fast-ice during the 19405 and 1950s. There was a pronounced sub-decadal cycle in fast-ice duration at the South Orkney Islands from the mid-1960s to 1990. In recent years this cyclicity has broken down and fast-ice duration has been greater than expected. Analyses of satellite data have shown that fast-ice duration at Signy Island reflects the larger-scale ice dynamics of the Wed dell Sea. Investigation of the Weddell Sea ice dynamics in relation to circumpolar ice extents indicates that the position of anomalies in the maximum sea-ice extent field precesses around the Antarctic continent with a period of approximately 7-9 years. Analysis of atmospheric and oceanic connections with the sea ice variability show that there are signals in both regimes. 1bis environmental variability has significant implications for ecosystem function and the detection of short-term and long-term ecological change.

A total of 45 pellets from the blue-eyed shag Phalacrocorax atriceps were collected in January 1994 at Duthoit Point, Nelson Island, South Shetland Islands. The analysis showed fish as the main prey, followed by octopods, polychaetes and gastropods. Notothenia coriiceps formed the bulk of the diet, but Harpagijer antarcticus was the most frequent and important fish in number. The prey represented in the pellets were consistent with those observed in stomach contents sampled simultaneously in the same colony; however, they differed in importance. A daily mean of 0.7 pellets per bird was collected, representing 255 g of fish. Correction factors previously estimated in a feeding trial were applied to this value, and suggested that the average daily amount of food ingested by an adult shag during the sampling period was 1325 g, which fall into the range observed by the analysis of stomach contents. Other aspects related to the feeding behavior of this bird are also discussed.

One hundred and seventy three regurgitated casts of the blue-eyed shag or imperial cormorant Phalacrocorax atriceps were collected in a colony at Half-moon Island, South Shetland Islands, by weekly sampling throughout the breeding season from December 1993 to February 1994. Demersal-benthic fish were the main prey (91% in number) followed by mollusks and polychaetes. Six fish species were represented: Notothenia coriiceps, Nototheniops nudifrons, Trematomus newnesi, Harpagifer antarcticus, Gobionotothen gibberifrons and Pagothenia bernacchii. Notothenia coriiceps was the most frequent (F%=73) and important in mass (79%), followed by N. nudifrons and T. newnesi. The overall composition of the diet was qualitatively and quantitatively similar to that reported for the 1992/93 austral summer at the same colony. However, the pellet analysis throughout the 1993/94 breeding season showed that large N. coriiceps were the main prey during the chick rearing period, whereas when chicks were fledging/post- fledging the diet was more diverse and comprised chiefly prey of lower energetic content like other smaller fish species and non- fish organisms. This may reflect different degrees of energy demand by chicks at different stages of the season.

Data from the acoustic surveys of MV SA "Aghulas" and FRV "Walter Herwig", and the 1981 RRS "John Biscoe" South Georgia acoustic survey were analyzed by geostatistical methods. Estimates of mean density (g m-2) of krill and their variances are compared with published results (Trathan et al., 1993 and Murphy et al., 1991) from statistical analyses based on random sampling theory. A further high-resolution geostatistical analysis of the MV SA "Aghulas" (ping-by-ping) data set of the density of each individual aggregation is also presented. These analyses illustrate the problems of applying geostatistical methods to data from highly aggregated species which can show marked skewness in their histogram of density.

Dual frequency (38 and 120 kHz) acoustic surveys of shelf-break regions in the vicinity of Willis Islands, South Georgia and Coronation Island, South Orkneys, both in the Atlantic sector of the Southern Ocean, were carried out from RRS lames Clark Ross during January 1994. Difference in signal strength between the two frequencies (δMVBS = MVBS 120 kHz - MVBS 38 kHz) was used to partition acoustic targets into three biological categories: Antarctic krill; nekton (larger than krill); and zooplankton (smaller than krill). To counter the absence of krill length-frequency data from Coronation Island a new generic target strength (TS) relationship was derived. This relationship was used in conjunction with appropriate 120 kHz data to calculate krill density estimates for both survey areas. Krill distribution in both regions was extremely patchy, resulting in a highly skewed frequency distribution of density; for example one echo-integration interval contained 104 times the mean krill density. An approximate six-fold difference in mean krill abundance was detected between the two areas, but in comparison with previously published density estimates krill densities in both regions were extremely low (1.7 and 10.7 gm-2 for Willis and Coronation Islands respectively). Gross regional differences in pelagic faunal composition were apparent from inspection of echo-charts, and were quantified in detailed analysis of acoustic signals. The water column in the vicinity of Willis Islands was characterised by a series of diffuse but continuous scattering layers visible only at 120 kHz, and 73% of acoustic targets there were classified as zooplankton. In marked contrast, the Coronation Island region was dominated by dense, discrete patches classified as larger nektonic scatterers, whereas only 12% of targets were classified as zooplankton. Simultaneous predator diet analyses carried out at Bird Island, South Georgia, confirm the profoundly low levels of krill availability, and support the acoustic observation that the Willis Island region contained large numbers of small zooplankton such as the amphipod Themisto gaudichaudii.

Dual frequency (38 and 120 kHz) acoustic surveys were carried out in two regions along the northern coast of South Georgia from RRS lames Clark Ross during January 1994. Difference in signal strength between the two frequencies (δMVBS = MVBS 120 kHz - MVBS 38 kHz) was used to discriminate krill from other acoustic targets. A generic target strength to weight relationship was used to derive krill densities from 120 kHz signals attributed krill. At less than 1 g m-2 , mean weighted krill densities in both regions were extremely low in comparison with previously published density estimates, and provide further evidence of an extreme krill paucity around South Georgia in the 1993/4 season.

Anomalies detected in the firmware of a Simrad EK500 echo-sounder are described so that users are aware of potential problems and how to solve them.