SEASONAL GROWTH AND MORTALITY OF EUPHAUSIA-SUPERBA IN ADMIRALTY BAY, SOUTH SHETLAND ISLANDS, ANTARCTICA

The mean size of adult and juvenile Euphausia superha in populations sampled during 1979-1986 in Admiralty Bay, South Shetland Islands, Antarctica shows a sinusoidal seasonal oscillation; mean krill size is reduced in winter. This has previously been interpreted as evidence of negative growth. Monthly total mortality was highest over winter, between July and October: there was notable interannual variability. We suggest that the winter-time decrease in mean krill size in Admiralty Bay results from predation reducing the numbers of larger, but less abundant krill, at a time when juvenile krill spawned the previous summer are recruiting to the population. This mechanism can explain the seasonal oscillation of mean krill size, without invoking negative growth. © 1991 Conseil International pour l'Exploration de la Mer.