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


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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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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 (13C) and stable nitrogen (15N)
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
Authors/Creators:Tierney, M
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