Temporal variability and evaluation of methods used to infer diet of a Southern Ocean predator, the Adélie penguin Pygoscelis adeliae

Tierney, M 2009 , 'Temporal variability and evaluation of methods used to infer diet of a Southern Ocean predator, the Adélie penguin Pygoscelis adeliae', PhD thesis, University of Tasmania.

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Available under University of Tasmania Standard License.

Abstract

Predicting ecosystem response to change and ensuring long-term sustainable management of Southern Ocean marine living resources is reliant upon ecosystem monitoring programmes that will provide data on key physical and biological components of the ecosystem and the functional relationships between these components. Integral to such monitoring programmes is accurate and reliable information on the diet of predators. In this study, I examined the long-term variability in the diet of Adélie penguins Pygoscelis adeliae, and their dependence on Antarctic krill Euphausia superba, the target of a large commercial fishery, to evaluate their effectiveness as an indicator species monitored to detect the effect of anthropogenic disturbance on the Southern Ocean ecosystem.
Krill and fish were the dominant prey items in the diet of Adélie penguins from Béchervaise Island, however there was substantial inter- and intra-annual variation, as well as differences between sexes, in meal mass and diet composition. In years of low amounts of krill in the diet, reproductive performance declined, indicating Adélie penguins from this region are dependent on krill and could be considered an effective indicator species. However the large year-to-year variability naturally present in Adélie penguin diet limits the power to detect change due to an impact over short time periods (i.e. <20-years), unless one is willing to relax Type I error levels above the traditional 0.05 level.
Diet of Adélie penguins has traditionally been inferred from stomach samples, however execution of this technique is restricted to when birds are accessible and have full stomachs. Hence, diet data is biased towards the chick-rearing period when adults bring food ashore to feed chicks. Therefore I evaluated two alternate, indirect techniques - stable-isotope analysis (SIA) and fatty acid signature analysis (FASA) - that may complement or enhance our knowledge of Adélie penguin diet.
Diet inferred from the analysis of stable carbon (δ$$^{13}$$C) and stable nitrogen (δ$$^{15}$$N) isotopes in penguin blood and feather samples, and from fatty acids in blood samples, was similar to that determined from stomach contents. Blood and feather samples analyzed by SIA or FASA can integrate diet over different time periods. Therefore I examined intraand inter-annual variation in the diet of adult and chick Adélie penguins. Although diet did not differ between age classes, it did vary between breeding stages and between the two years of study. I also developed an in situ method to calibrate blood FA profiles with stomach contents, which offers a simple and effective alternative to more complex calibration techniques developed elsewhere. I conclude that SIA and FASA are useful for monitoring Adélie penguin diet at broad taxonomic resolutions, and, combined with stomach content analysis, provide a more comprehensive picture of Adélie penguin foraging ecology. Additionally, and most importantly, these techniques extend the temporal window for obtaining diet information, including those periods when it is difficult to use conventional sampling techniques, although penguins may be vulnerable to impacts such as commercial fishing during these periods as well.

Item Type: Thesis - PhD Tierney, M Copyright © 2009 the author Chapter 2 appears to be the equivalent of the peer reviewed version of the following article: Tierney, M., Emmerson, L., Hindell, M., 2009. Temporal variation in Adélie penguin diet at Béchervaise Island, east Antarctica and its relationship to reproductive performance, Marine biology, 156(8), 1633-1645, which has been published in final form at https://doi.org/10.1007/s00227-009-1199-9. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived VersionsChapter 4 appears to be the equivalent of a post-print version of an article published as: Tierney, M., Southwell, C., Emmerson, L. M., Hindell, M. A., 2008. Evaluating and using stable-isotope analysis to infer diet composition and foraging ecology of Adélie penguins Pygoscelis adeliae, Marine ecology progress series 355, 297-307Chapter 4 appears to be the equivalent of a post-print version of an article published as: Tierney, M., Nichols, P. D., Wheatley, K. E., Hindell, M. A., 2008. Blood fatty acids indicate inter- and intra-annual variation in the diet of Adélie penguins: comparison with stomach content and stable isotope analysis, Journal of experimental marine biology and ecology, 367(2), 65-74 View statistics for this item