Abstract
Krill (Euphausia superba) carapace measurements (length and width; mm) collected from plankton tows in the South Shetland Islands (SSI), Antarctica are used to test the generality of a common discriminant function developed to reconstruct krill length frequencies in Antarctic fur seal diets for the area surrounding South Georgia (SG). Total length and sex ratio of krill in the SSI were overestimated by 5.6 and 154%, respectively, when the SG allometric equations were applied to 3 years (2003–2005) of data. These errors arise and increase as a result of krill population dynamics, specifically recruitment that contributes large proportions of immature krill, misclassified as males by the SG discriminant function. We develop sex-specific regression models based on separate discriminant functions that provide significantly better discriminatory power. However, our analysis indicates that reconstructions of krill sex ratio and length composition in the ocean environment are less reliable in years when the ratio of immature to mature krill is high. For the SSI area, five out of 14 years (35.7%) surveyed (1992–2005) had proportions of immature to mature adult krill ≥ 0.50.
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Acknowledgments
This work was supported as part of the National Oceanic and Atmospheric Administration’s U.S. Antarctic Marine Living Resources Program. We wish to thank Dr. R.S. Holt, Director of U.S. AMLR for his encouragement and support and the captain and crew of the R/V YUZHMORGEOLOGIYA for their support while in the field. We thank all those involved in measuring krill for this study: Anne Allen, Lindsay Smith, and Margi Cooper. Finally, we wish to thank an anonymous reviewer for suggestions that greatly improved the paper.
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Goebel, M.E., Lipsky, J.D., Reiss, C.S. et al. Using carapace measurements to determine the sex of Antarctic krill, Euphausia superba . Polar Biol 30, 307–315 (2007). https://doi.org/10.1007/s00300-006-0184-8
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DOI: https://doi.org/10.1007/s00300-006-0184-8