CCAMLR

In the period from 24 February to 7 March 1996 in the cruise of RV "Atlantida" acoustic assessment of krill biomass and distribution was carried out in study area restricted with 59° 10' S - 60°30' S and 42 °00' W - 50°00 'w within Subarea 48.2. The study area of 19.200 sq.mi1es was located in the zone of two circulation systems of climatic scale interaction: Antarctic Circumpolar Current and Weddell Sea water circulation. Researches in the study area included a broad spectrum of hydrobiological and oceanographic observations and studies.Onboard hydroacoustic complex was represented by the measuring system EK-5001BI 500. Calibration of echo sounder EK-500 was performed by specialists of Simrad company in Horten, Norway. Echosurvey was carried out using uniform square grid of tacks with between-tacks distance of 20 miles. The echosurvey was carried out diurnally. Krill target strength was estimated by means of TS/length relationship, recommended by WG-krill (SC-CAMLR, 1991). Recorded range of MSBS values variations was (-77÷-43) dB. Kri11 biomass estimation in the study area amounted to 1.12 mln. t at 95% confidence limit CL=93.1 thous.t. Variation coefficients of krill density and biomass within strata speciefied exceeded no 8%. Previous data obtained by AtlantNIRO showed that biomass estimated was below that expected. One of the reasons is diurnal regime of echo survey execution. According to Demer and Hewitt (1995) exclusion of kri11 vertical diurnal migrations from consideration results in underestimated acoustic biomass by 1.9 dB at s.d. = 0.6 dB. Besides, the study area selected included no the southern part (southwards of 60 ° 30'S) of Subarea 48.2 where southwards off Coronation Island considerable kri11 fishing grounds occure. According to AtlantNIRO data krill biomass southwards of 60 ° 30'S amounts about (883±264.9) thous. t.
Therefore, total krill biomass in Subarea 48.2 may be assessed as 2.6 mln.t at 95(% confidence limit CL=298.2 thous.t

There are presented some results of atmospheric circulation features evaluation over Antarctic Sector of Atlantic, thermochaline conditions and surface geostrophic transfers.
There are obtained daily indeses of atmospheric circulation for the period February-March 1996, calculated average values for ten-days periods and for month.
There are calculated cyclogenesis intensity characteristics for the period, which along with atmospheric circulation data allow to determine atmospheric circulation features over ASA area at the summer period.
There are obtained data on thermochaline conditions on the polygon near South Orkneys. There are calculated and presented maximum temperature distribution on the polygon, allowing to provide the most clear marking of the main water masses and Secondary Frontal Zone position and geostrophical current velocities distribution in the limits of the polygon investigated.
There are observed exceeding of the atmospheric circulation in the period of investigation (February-March of 1996) over the average for many years one and predominance of the meridional transfer over the zonal one.
There are stated the negative anomalies of the thermochaline characteristics in the subarea 48.02.
The presence of Doubling Anticyclonic Current is revealed near the South Orkneys.

In the paper the attempt was made to compare selective features of several midwater krill trawls within the frame of krill density precise estimates provision problem in echo-surveys. The results of fishing one krill aggregation with two types of trawls (PT 72/308 commercial trawl and Isaacs-Kidd research trawl IKTM) are presented. Selectivity differences of those trawls resulted in significant variability of krill size composition in catches. Average krill length differed more than in 6 mm which caused deviations of TS values, estimated with TS/length relationship (SC-CAMLR, 1991) in ΔTS=2.1 dB. Associated variation in density estimates for the same MSBS value amounted to 1.65 .
Theoretical study of trawl selectivity features was carried out using statistical model. It was shown that selectivity of midwater trawl depended both on its design, trawling velocity, and catch value. Trawl selectivity features will especially affect the estimates of composition, abundance and biomass by krill size groups, and primarily in young krill assessment.
Analysis of abundance biomass estimates on the basis of various echo-surveys data requires to take into consideration selective features of trawl used.

Twenty eight stomach contents of the South Polar Skua Catharacta maccormicki were collected throughout the breeding season at Half-moon Island, South Shetland Islands, Antarctica. The analysis of the samples indicated that fish were the most frequent prey (100%) and also predominated in mass (98%) and that their importance remained constant all along the study period. Eight fish species were identified (Electrona antarctica, Pleuragramma antarcticum, Krefftichthys anderssoni, Champsocephalus aceratus, Gymnoscopelus braueri, Electrona carlsbergi, Protomyctophum normani and Protomyctophum tenisoni) being E. antarctica the most important prey. The unexpected fish importance in the diet composition as well as its implication for CCAMLR are commented.

In this document we inform on the results of six years monitoring changes in the diet of the Blue-eyed Shag Phalacrocorax atriceps as reflected by the analysis of regurgitated pellets collected at two localities of the South Shetland Islands. The comments are mainly focused on Gobionotothen gibberifrons and Notothenia rossii, species of particular interest for CCAMLR. Notothenia rossii appeared in the diet of this bird in the lasts years and the importance of G. gibberifrons fluctuated without trends but, overall, the contribution of these two species to the diet of the Blue-eyed Shag remains low.

A major biological/physical survey of the waters off East Antarctica was carried out between January and April 1996. The focus was on the distribution and abundance of Antarctic krill in CCAMLR Statistical Area 58.4.1 but in addition, measurements were also made on a whole suite of oceanographic and biological variables over the entire survey area. This paper summarises the range of variables measured and provides an overview of some preliminary results.

In January-March 1996 a hydroacoustic survey for Antarctic krill was conducted in CCAMLR Division 58.4.1 for the purposes of estimating overall biomass (B0). The krill biomass in the area surveyed (873,000 km2) was estimated to be 6.67 million tonnes with a CV of 27%. Krill were more abundant in the west of the survey area 800-1200E than in the 120°-150°E region. The majority of the krill detected were found in the top 80 metres of the water column.

The CCAMLR Ecosystem Monitoring Programme has two aims: to detect changes in critical components of the antarctic ecosystem, and to distinguish between changes due to the harvesting of commercial species and changes due to environmental variability. Data from Seal Island are used to construct a multivariate model which relates chinstrap penguin breeding success, krill abundance and sea ice conditions, which effectively predicts chinstrap success given sea-ice data with an R2 of 0.914. This model is then used to propose a method of distinguishing between effects of environmental variation and harvesting on chinstrap breeding success. Other Antarctic Peninsula predator parameters are also briefly analysed. The results demonstrate that this methodology could be applied to other CEMP sites, even with the relatively short time series now available, and provides a way forward in the analysis and interpretation of the CEMP indices.