CCAMLR

In connection with future calculation of volume of krill immigration/emigration (flux) in the choosen polygones, the proves of active long-distance migrations of krill are considered. These proves are not undoubted. The most difficult problem, which nevertheless should determine the results of calculations, is the valuation of krill retention time. To make it more correct and natural it is necessary to take into account the biological characteristics of krill, especially for the regions outside the shelf and slope areas of investigating regions.

Krill sampling was carried out onboard RV ‘Polarstem’ from January 25 to March 11, 1994 south of 66°S, between 68°W and 120°W. Krill Euphausia superba abundance and biomass was in the lower range of values generally found in the Antarctic Peninsula and Elephant Island region. A distinct spatial separation for size groups was observed for krill, with small size groups being more abundant in the East Wind Drift zone and larger ones further north under the influence of West Wind Drift waters. The overall krill length frequency distribution was similar to the composition reported from the South Shetland Island region for the same summer period. The recruitment index for krill indicated a poor recruitment success of the 1992/93 year-class in the region (R1 = 0.076). Both results indicate large scale effects on the krill stock. Spawning was late during the studied season, no larvae were found in the area. These findings were discussed in the light of recently described correlations between winter sea-ice conditions, krill spawning and recruitment success and let to the conclusion that recruitment of the 1993/94 kri11 year-class will be poor.

Based on a data set sampled during November/December 1994 in the Elephant Island Plateau Region by RV POLARSTERN, a water mass analysis is performed which reveals the approximate location of the Weddell-Scotia Confluence. Vertical distribution of oceanographic parameters temperature, salinity and density is discussed. Geopotential anomaly charts, referenced to different pressure levels outline the genera! flow as given by the geostrophic part of the circulation. Compared to American field observations during January 1994, and to historic data, the spring 1994 data indicate that 1994 spring was colder than in previous years in the Elephant Island Plateau Region. Since the data base available to the author is very much limited to answer questions on year-to-year changes, or even on climatic time scales, it is recommended to do a cooperative analysis of data sampled throughout the years in the Elephant Island Plateau Region

Between year variability of krill year class success and recruitment during the 1977-1994 period are described based on data from German expeditions and U.S. Antarctic Marine Living Resources Program cruises in the Elephant Island area. The recruitment index (R1), based on the relative abundance of the 1 + age class, varies substantially between years, whereas it is quite similar between different surveys within the same field season. The overall mean recruitment index for all years was Rmean = 0.210. Good recruitment was observed for the 1980/81, 1985/86, 1987/88, and 1990/91 year classes; exceedingly poor recruitment occurred for the 1976/77, 1982/83, 1983/84, 1988/89, 1991/92 and 1992/93 year classes. Pairwise correlations between the stock parameters, recruitment indices and available environmental data indicate that good and poor year class success are directly and indirectly related to sea ice conditions during the preceding winter season, the timing of krill spawning, and the occurrence of dense salp concentrations. No correlation is shown with upper water column temperature or krill stock/spawning stock size. A concept is developed describing the interactions of various parameters leading to good or poor krill recruitment.