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Marine Biology

, Volume 161, Issue 10, pp 2243–2255 | Cite as

Higher trophic level prey does not represent a higher quality diet in a threatened seabird: implications for relating population dynamics to diet shifts inferred from stable isotopes

  • Kyle W. Morrison
  • Sarah J. Bury
  • David R. Thompson
Original Paper

Abstract

Diet quality is a key determinant of population dynamics. If a higher trophic level, more fish-based diet is of higher quality for marine predators, then individuals with a higher trophic level diet should have a greater body mass than those feeding at a lower trophic level. We examined this hypothesis using stable isotope analysis to infer dietary trophic level and foraging habitat over three years in eastern rockhopper penguins Eudyptes chrysocome filholi on sub-Antarctic Campbell Island, New Zealand. Rockhopper penguins are ‘Vulnerable’ to extinction because of widespread and dramatic population declines, perhaps related to nutritional stress caused by a climate-induced shift to a lower trophic level, lower quality diet. We related the stable nitrogen (δ15N) and carbon (δ13C) isotope values of blood from 70 chicks, 55 adult females, and 55 adult males to their body masses in the 2010, 2011, and 2012 breeding seasons and examined year, stage, age, and sex differences. Opposite to predictions, heavier males consumed a lower trophic level diet during incubation in 2011, and average chick mass was heavier in 2011 when chicks were fed a more zooplankton-based, pelagic/offshore diet than in 2012. Contrary to the suggested importance of a fish-based diet, our results support the alternative hypothesis that rockhopper penguin populations are likely to be most successful when abundant zooplankton prey are available. We caution that historic shifts to lower trophic level prey should not be assumed to reflect nutritional stress and a cause of population declines.

Keywords

High Trophic Level Falkland Island Rockhopper Penguin Adult Body Mass Magellanic Penguin 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Notes

Acknowledgments

Our thanks to the two anonymous reviewers of this manuscript for constructive comments. P. Battley, D. Armstrong, P. Sagar, and S. Jamieson provided helpful comments and discussion. Thanks to J. Brown for conducting the SIA. Our methods were approved by the Massey University Animal Ethics Committee, protocol no. 10/90. K.W.M. is grateful to Massey University, the Natural Sciences and Engineering Research Council of Canada, and Education New Zealand for financial support. This work was supported by the New Zealand Ministry of Business, Innovation, and Employment (contract C01X0905 to the National Institute for Water and Atmospheric Research). Additional research funding was generously provided by the J.S. Watson Conservation Trust of the Royal Forest and Bird Protection Society of New Zealand, the Hutton Fund of The Royal Society of New Zealand, and the Penguin Fund of Japan. We are grateful to S. Cockburn at the New Zealand Department of Conservation, National Office for providing RFID data loggers. Thank you to the Department of Conservation, Southland Conservancy for supporting our research on Campbell Island, and to H. Haazen and the crew of RV ‘Tiama’ for safe transport. This research would not have been possible without the skillful penguin-wrangling of N. Morrison, R. Buchheit, and R. Dunn.

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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Kyle W. Morrison
    • 1
    • 2
  • Sarah J. Bury
    • 2
  • David R. Thompson
    • 2
  1. 1.Ecology Group, Institute of Natural ResourcesMassey UniversityPalmerston NorthNew Zealand
  2. 2.National Institute of Water and Atmospheric ResearchHataitai, WellingtonNew Zealand

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