In the Antarctic Peninsula, during the chick-rearing period Adélie (Pygoscelis adeliae) and gentoo (P. papua) penguins feed primarily on Antarctic krill (Euphausia superba), which is also exploited by the commercial fishery. Krill length and proportion of juvenile krill consumed by these predators that breed at Stranger Point, South Shetland Islands (from 2007/2008 to 2015/2016), and those collected by the krill fishery in the Mar de la Flota/Bransfield Strait (from 2009/2010 to 2015/2016) were compared to evaluate the potential of each data source as an indicator of changes in the size composition and so, in the demographic structure of the krill population. Overall, the mean krill size taken by gentoo penguins was larger than that ingested by Adélie penguins, which consumed higher proportions of juvenile (≤ 35 mm) and one-year-old (≤ 25 mm) krill. Although the krill size caught by the fishery was statistically similar to that taken by both penguin species, there were differences in the frequency distributions of krill size among the three databases. Furthermore, when only adult krill (> 35 mm) was considered, the three sources of krill data showed a similar inter-annual variation in the availability of adult krill cohorts. Our findings suggest that each database analysed here can potentially provide different information (although complementary) about krill size composition. In addition, inter-annual fluctuations in the smaller size classes of krill likely reflect their first year of recruitment and, therefore, may be used as an indicator of shifts in local krill availability.
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The penguin datasets analysed during the current study are available from the corresponding author on reasonable request. The krill fishery dataset that supports the findings of this study is available from the CCAMLR’s Secretariat but restrictions apply to the availability of these data, which were used under license for the current study, and so are not publicly available.
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We thank all field and laboratory assistants who helped collecting and analysing stomach content samples associated with this study. The authors also thank the scientific observers working as part of the CCAMLR Scheme of International Scientific Observation who collected the krill length data from the fishery and the CCAMLR’s Secretariat for providing the data extract of these data. We thank the anonymous reviewers and editors for their helpful comments and suggestions on improving the manuscript. Finally, we are very grateful to Jorge M. Viccichi and Claudio Matko for their unconditional support and their significant contributions.
The FONCYT—Agencia Nacional de Promoción Científica y Tecnológica (Grant: PICTO 2010-0111) and the Instituto Antártico Argentino – Dirección Nacional del Antártico (PINST-05) provided financial and logistical support.
Conflict of interest
The authors declare that they have no conflict of interests. The krill fishery data was provided by the CCAMLR’s Secretariat (Hobart, Tasmania) and has been published in accordance with the rules adopted by the Twenty-Second Meeting of the Commission (CCAMLR-XXII, paragraphs 12.1 to 12.6; https://www.ccamlr.org/en/document/publications/rules-access-and-use-ccamlr-data).
All procedures involving Adélie and gentoo penguins were conducted under appropriate international, national and/or institutional guidelines for the care and use of animals. All necessary approvals were obtained. Each year, sampling was completed under the permit granted by the Dirección Nacional del Antártico (Environmental Management Office).
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Juáres, M.A., Grech, M.G., Casaux, R. et al. Size structure of Antarctic krill inferred from samples of Pygoscelid penguin diets and those collected by the commercial krill fishery. Mar Biol 168, 22 (2021). https://doi.org/10.1007/s00227-021-03831-0
- Pygoscelis adeliae
- Pygoscelis papua
- SISO database
- Euphausia superba