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Marine Ecology Progress Series

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MEPS 547:61-78 (2016)  -  DOI:

Growth and shrinkage in Antarctic krill Euphausia superba is sex-dependent

G. A. Tarling1,*, S. Hill1, H. Peat1, S. Fielding1, C. Reiss2, A. Atkinson3

1British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
2Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, La Jolla, CA 92037, USA
3Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth PL1 3DH, UK
*Corresponding author:

ABSTRACT: The ability of Antarctic krill Euphausia superba Dana to withstand the overwintering period is critical to their success. Laboratory evidence suggests that krill may shrink in body length during this time in response to the low availability of food. Nevertheless, verification that krill can shrink in the natural environment is lacking because winter data are difficult to obtain. One of the few sources of winter krill population data is from commercial vessels. We examined length-frequency data of adult krill (>35 mm total body length) obtained from commercial vessels in the Scotia-Weddell region and compared our results with those obtained from a combination of science and commercial sampling operations carried out in this region at other times of the year. Our analyses revealed body-length shrinkage in adult females but not males during winter, based on both the tracking of modal size classes over seasons and sex-ratio patterns. Other explanatory factors, such as differential mortality, immigration and emigration, could not explain the observed differences. The same pattern was also observed at South Georgia and in the Western Antarctic Peninsula. Fitted seasonally modulated von Bertalanffy growth functions predicted a pattern of overwintering shrinkage in all body-length classes of females, but only stagnation in growth in males. This shrinkage most likely reflects morphometric changes resulting from the contraction of the ovaries and is not necessarily an outcome of winter hardship. The sex-dependent changes that we observed need to be incorporated into life cycle and population dynamic models of this species, particularly those used in managing the fishery.

KEY WORDS: Southern Ocean · Population dynamics · Production · Life cycle · Fishery

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Cite this article as: Tarling GA, Hill S, Peat H, Fielding S, Reiss C, Atkinson A (2016) Growth and shrinkage in Antarctic krill Euphausia superba is sex-dependent. Mar Ecol Prog Ser 547:61-78.

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