Inter- and intra-annual variability of commercial krill trawling positions for the 1980/81 to 1999/2000 seasons in the area north of the South Shetland Islands were analysed in relation to biological and environmental factors. Commercial fishing operations concentrated on the outer shelf in the early 1980s, along the shelf slope in the mid to late 1980s, and from the shelf across to the outer shelf in the early to late 1990s. Intra-annually, trawling positions generally started from the outer shelf and proceeded towards the shelf later in the season. Trawling positions seemed to be primarily governed by the distribution of larger mature krill, especially at the beginning of fishing operations each season. In summer, biological factors that affect product quality, such as salp abundance and the proportion of green krill, also seemed to have an increasing effect on trawling positions. Ice conditions for recent fishing periods were also demonstrated to have an effect.