RECRUITMENT OF ANTARCTIC KRILL EUPHAUSIA-SUPERBA AND POSSIBLE CAUSES FOR ITS VARIABILITY

Between-year variability of krill Euphausia superba year class success and recruitment during the 1977 to 1994 period are described based on data from German expeditions and U.S. Antarctic Marine Living Resourc es Program cruises in the Elephant Island area. The recruitment index (R(1)), based on the relative abundance of the 1+ age class, varies su bstantially between years, whereas it is quite similar between differe nt surveys within the same field season. The overall mean recruitment index for all years was R(mean) = 0.210. Good recruitment was observed for the 1980/81, 1985/86, 1987/88, and 1990/91 year classes; exceedin gly poor recruitment occurred for the 1976/77, 1982/83, 1983/84, 1988/ 89, 1991/92 and 1992/93 year classes. Pairwise correlations between th e stock parameters, recruitment indices, and available environmental d ata indicate that good and poor year class success are directly and in directly related to sea ice conditions during the preceding winter sea son, the timing of krill spawning, and the occurrence of dense salp co ncentrations. No correlation is shown with upper water column temperat ure or krill stock/spawning stock size. A concept is developed describ ing the interactions of various parameters leading to good or poor kri ll recruitment.