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A female Antarctic krill loses 34% of its body mass when it lays a batch of eggs. This represents a considerable input of energy which was estimated using a combination of measured mass and energy differences in female krill and from the measured energetic content of ovarian tissue. Large (c. 50 mm) female krill lose 2.9–3.8 kJ each time a batch of eggs is laid. Calculations using this figure indicate that multiple spawning by Antarctic krill in a season would require above average phytoplankton concentrations (> 0.5 μg chl a 1−1) and filtration rates which are close to the maximum reported (> 10 l h−1).

Changes in the extent of Antarctic sea-ice are difficult to quantify for the pre-satellite era. The available direct data are sparse. A substantially larger set of proxy records based on whaling positions indicated a large shift in whaling positions between the 1930s to 1950s compared with whaling positions in the 1970s to mid 1980s. However, these findings have been questioned. Further analyses here using historic ice charts, direct sea-ice observations and whaling positions agree that a substantial southward shift in the ice-edge did occur. The analyses indicate the average change is around 1.89 • to 2.80 • of latitude with a reasonable mid-range estimate of 2.41 • . Regional analyses show that the largest changes occurred in the South Atlantic, but change is also detected across the Indian Ocean to the Ross Sea; a 220 • span of longitude. A recently published proposition that the shift in ice-edges is an artefact caused by bias in the satellite derived records is not supported.

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