Letter | Published:

Long-term decline in krill stock and increase in salps within the Southern Ocean

Nature volume 432, pages 100103 (04 November 2004) | Download Citation



Antarctic krill (Euphausia superba) and salps (mainly Salpa thompsoni) are major grazers in the Southern Ocean1,2,3,4, and krill support commercial fisheries5. Their density distributions1,3,4,6 have been described in the period 1926–51, while recent localized studies7,8,9,10 suggest short-term changes. To examine spatial and temporal changes over larger scales, we have combined all available scientific net sampling data from 1926 to 2003. This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s. Spatially, within their habitat, summer krill density correlates positively with chlorophyll concentrations. Temporally, within the southwest Atlantic, summer krill densities correlate positively with sea-ice extent the previous winter. Summer food and the extent of winter sea ice are thus key factors in the high krill densities observed in the southwest Atlantic Ocean. Krill need the summer phytoplankton blooms of this sector, where winters of extensive sea ice mean plentiful winter food from ice algae, promoting larval recruitment7,8,9,10,11 and replenishing the stock. Salps, by contrast, occupy the extensive lower-productivity regions of the Southern Ocean and tolerate warmer water than krill2,3,4,12. As krill densities decreased last century, salps appear to have increased in the southern part of their range. These changes have had profound effects within the Southern Ocean food web10,13.

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We thank V. Loeb and R. Hewitt for sharing the extensive data from the AMLR Program; A. Clarke, G. Hosie, S. Chiba, J. Nishikawa, R. Anadón, P. Ward and A. de C. Baker for providing further data and information; P. Fretwell, A. Fleming, S. Grant and S. Thorpe for data handling; and A. Hirst, A. Clarke, P. Ward, K. Schmidt, D. Pond, P. Trathan, G. Tarling and E. Murphy for comments. Satellite data were provided courtesy of NASA GSFC, the SeaWiFS Project and NOAA. The Department of Environmental Affairs & Tourism (Pretoria, South Africa) provided funds and facilities for South African collections, through the South African National Antarctic Program. A.A.'s contribution was funded under the British Antarctic Survey's DYNAMOE Programme.

Author information


  1. British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 OET, UK

    • Angus Atkinson
  2. Sea Fisheries Institute, Palmaille 9, 22767 Hamburg, Germany

    • Volker Siegel
  3. Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Rd, Vancouver, British Columbia, V6T 1Z4, Canada

    • Evgeny Pakhomov
  4. Department of Zoology, Faculty of Science and Technology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa

    • Evgeny Pakhomov
  5. NERC Centre for Ecology and Hydrology, CEH Monks Wood, Abbots Ripton, Huntingdon PE28 2LS, UK

    • Peter Rothery


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Competing interests

The authors declare that they have no competing financial interests.

Corresponding author

Correspondence to Angus Atkinson.

Supplementary information

Word documents

  1. 1.

    Supplementary Information Main Text

    Focus on the three key results of the paper, expanding on their robustness to possible artefacts of sampling. Includes Supplementary Information tables 3and 4, and Supplementary Figure captions.

Excel files

  1. 1.

    Supplementary Table 2

    Data collection information — metadata for the complete database (follows main text table 1).

Powerpoint files

  1. 1.

    Supplementary Figure 4

    Krill distribution (follows main text Figs 1–3).

  2. 2.

    Supplementary Figure 5

    Fine-scale sampling coverage in the South West Atlantic sector.

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